Effect of Glucosamine on Intraocular Pressure and Risk of Developing Glaucoma

PRCIS

Glucosamine supplementation is common but can be associated with increased intraocular pressure (IOP) and could contribute to the pathogenesis of glaucoma. It may be prudent for ophthalmologists to elicit any history of glucosamine use from their patients and advise them accordingly. Further studies on the role of glucosamine in glaucoma are warranted.

BACKGROUND

The most frequently recommended slow-acting medication for osteoarthritis symptoms is glucosamine, although its effectiveness is questionable. Widely used glucosamine sulfate supplements may increase IOP.

METHODS

In the current study, we analyzed online databases such as UK Biobank, MedWatch, and FinnGen to evaluate the relationship between glucosamine and IOP and glaucoma. We included budesonide and fluticasone in the analysis for comparison since these drugs are associated with increased IOP.

RESULTS

In UK Biobank subjects, glucosamine use was associated with increased corneal compensated IOP ( P =0.002, 2-tailed t test). This was also true in subjects without glaucoma ( P =0.002, 2-tailed t test). However, no significant association between glucosamine and IOP was detected in subjects with a diagnosis of glaucoma. In MedWatch, 0.21% of subjects taking glucosamine reported glaucoma, 0.29% of subjects using budesonide reported glaucoma, and 0.22% of subjects using fluticasone reported glaucoma. In contrast, 0.08% of subjects using any other drug reported glaucoma. This variability is significant ( P <0.001, 2-tailed Fisher exact test). Data from FinnGen on the risk of primary open angle glaucoma or glaucoma in subjects using glucosamine before the diagnosis of the disease revealed a significantly increased risk for both primary open angle glaucoma (hazard ratio: 2.35) and glaucoma (hazard ratio: 1.95).

CONCLUSION

Glucosamine supplementation is common but can be associated with increased IOP and could contribute to the pathogenesis of glaucoma. It may be prudent for ophthalmologists to elicit any history of glucosamine use from their patients and advise them accordingly. Further studies on the role of glucosamine in glaucoma are warranted.

Genes as drugs for glaucoma: latest advances

PURPOSE OF REVIEW

To provide the latest advances on the future use of gene therapy for the treatment of glaucoma.

RECENT FINDINGS

In preclinical studies, a number of genes have been shown to be able to reduce elevated intraocular pressure (IOP), and to exert neuroprotection of the retinal ganglion cells. These genes target various mechanisms of action and include among others: MMP3 , PLAT, IκB, GLIS, SIRT, Tie-2, AQP1. Some of these as well as some previously identified genes ( MMP3, PLAT, BDNF, C3, TGFβ, MYOC, ANGPTL7 ) are starting to move onto drug development. At the same time, progress has been made in the methods to deliver and control gene therapeutics (advances in these areas are not covered in this review).

SUMMARY

While preclinical efforts continue in several laboratories, an increasing number of start-up and large pharmaceutical companies are working on developing gene therapeutics for glaucoma ( Sylentis, Quetera/Astellas, Exhaura, Ikarovec, Genentech, Regeneron, Isarna, Diorasis Therapeutics ). Despite the presence of generic medications to treat glaucoma, given the size of the potential world-wide market (∼$7B), it is likely that the number of companies developing glaucoma gene therapies will increase further in the near future.

Rethinking Prophylactic Laser Peripheral Iridotomy in Primary Angle-Closure Suspects: A Review

PURPOSE

To examine the generalizability, discuss limitations, and critically appraise recommendations on the management of primary angle-closure suspects (PACSs) that emerged as a result of recent randomized clinical trials challenging the widely accepted clinical practice of offering laser peripheral iridotomy (LPI) to PACS patients. To synthetize findings from these and other studies.

DESIGN

Narrative review.

SUBJECTS

Patients classified as PACS.

METHODS

The Zhongshan Angle-Closure Prevention (ZAP)-Trial and the Singapore Asymptomatic Narrow Angle Laser Iridotomy Study (ANA-LIS) along with accompanying publications were reviewed. Epidemiologic studies reporting on the prevalence of primary angle-closure glaucoma and other precursor forms of the disease were also analyzed along with publications reporting on the natural course of the disease or studies reporting on outcomes after prophylactic LPI.

MAIN OUTCOME MEASURES

Incidence of progression to more severe forms of angle closure.

RESULTS

Patients recruited in recent randomized clinical trials are asymptomatic, do not have cataracts, may be younger, and have, on average, deeper anterior chambers depth compared with patients treated with LPI in clinics.

CONCLUSIONS

The ZAP-Trial and ANA-LIS clearly represent the best available data on PACS management, additional parameters however may need to be considered when physicians face patients in clinic. PACS patients encountered at tertiary referral centers may represent more advanced cases with respect to ocular biometric parameters and may be at higher risk for disease progression compared with those recruited through population-based screening.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Recreating the Trabecular Outflow Tissue on Implantable, Micropatterned, Ultrathin, Porous Polycaprolactone Scaffolds

Glaucoma, where increased intraocular pressure (IOP) leads to damage to the optic nerve and loss of sight, is amongst the foremost causes of irreversible blindness worldwide. In primary open angle glaucoma, the increased IOP is a result of the malfunctioning human trabecular meshwork (HTM) cells' inability to properly regulate the outflow of aqueous humor from the eye. A potential future treatment for glaucoma is to replace damaged HTM cells with a tissue-engineered substitute, thus restoring proper fluid outflow. Polycaprolactone (PCL) is a versatile, biodegradable, and implantable material that is widely used for cell culture and tissue engineering. In this work, PCL scaffolds were lithographically fabricated using a sacrificial process to produce submicron-thick scaffolds with openings of specific sizes and shapes (e.g., grid, hexagonal pattern). The HTM cell growth on gelatin-coated PCL scaffolds was assessed by scanning electron microscopy, tetrazolium metabolic activity assay, and cytoskeletal organization of F-actin. Expression of HTM-specific markers and ECM deposition were assessed by immunocytochemistry and qPCR analysis. Gelatin-coated, micropatterned, ultrathin, porous PCL scaffolds with a grid pattern supported proper HTM cell growth, cytoskeleton organization, HTM-marker expression, and ECM deposition, demonstrating the feasibility of using these PCL scaffolds to tissue-engineer implantable, healthy ocular outflow tissue.

Age-Related Differences in Ocular Features of a Naturalistic Free-Ranging Population of Rhesus Macaques

Purpose

Rhesus macaques (Macaca mulatta) are the premier nonhuman primate model for studying human health and disease. We investigated if age was associated with clinically relevant ocular features in a large cohort of free-ranging rhesus macaques from Cayo Santiago, Puerto Rico.

Methods

We evaluated 120 rhesus macaques (73 males, 47 females) from 0 to 29 years old (mean ± SD: 12.6 ± 6.4) from September to December 2021. The ophthalmic evaluation included intraocular pressure (IOP) assessment, corneal pachymetry, biomicroscopy, A-scan biometry, automated refraction, and fundus photography after pupil dilation. The associations of age with the outcomes were investigated through multilevel mixed-effects models adjusted for sex and weight.

Results

On average, IOP, pachymetry, axial length, and automated refraction spherical equivalent were 18.37 ± 4.68 mmHg, 474.43 ± 32.21 µm, 19.49 ± 1.24 mm, and 0.30 ± 1.70 diopters (D), respectively. Age was significantly associated with pachymetry (β coefficient = -1.20; 95% confidence interval [CI], -2.27 to -0.14; P = 0.026), axial length (β coefficient = 0.03; 95% CI, 0.01 to 0.05; P = 0.002), and spherical equivalent (β coefficient = -0.12; 95% CI, -0.22 to -0.02; P = 0.015). No association was detected between age and IOP. The prevalence of cataracts in either eye was 10.83% (95% CI, 6.34-17.89) and was significantly associated with age (odds ratio [OR] = 1.20; 95% CI, 1.06-1.36; P = 0.004). Retinal drusen in either eye was observed in 15.00% (95% CI, 9.60-22.68) of animals, which was also significantly associated with age (OR = 1.14; 95% CI, 1.02-1.27; P = 0.020).

Conclusions

Rhesus macaques exhibit age-related ocular associations similar to those observed in human aging, including decreased corneal thickness, increased axial length, myopic shift, and higher prevalence of cataract and retinal drusen.

Consensus Recommendation for Mouse Models of Ocular Hypertension to Study Aqueous Humor Outflow and Its Mechanisms

Due to their similarities in anatomy, physiology, and pharmacology to humans, mice are a valuable model system to study the generation and mechanisms modulating conventional outflow resistance and thus intraocular pressure. In addition, mouse models are critical for understanding the complex nature of conventional outflow homeostasis and dysfunction that results in ocular hypertension. In this review, we describe a set of minimum acceptable standards for developing, characterizing, and utilizing mouse models of open-angle ocular hypertension. We expect that this set of standard practices will increase scientific rigor when using mouse models and will better enable researchers to replicate and build upon previous findings.

Tissue plasminogen activator rescues steroid-induced outflow facility reduction via non-enzymatic action

PURPOSE

Tissue plasminogen activator (tPA) prevents steroid-induced reduction in aqueous humor outflow facility; however, its mechanism of action at the trabecular meshwork (TM) remains unclear. Enzymatic and non-enzymatic domains allow tPA to function as both an enzyme and a cytokine. This study sought to determine whether cytokine activity is sufficient to rescue steroid-induced outflow facility reduction.

METHODS

Outflow facility was measured in C57BL/6J mice following triamcinolone acetonide exposure and either transfection of the TM using adenoviral vectors, encoding for enzymatically active and inactive tPA, or administration of the respective proteins. Protein injections were also administered to tPA deficient (PlatKO) and Mmp-9 deficient (Mmp-9KO) mice to determine the potential to rescue reductions in outflow facility and determine downstream mechanisms. Gene expression of matrix metalloproteinases (Mmp-2, -9, and -13) was measured in angle ring tissues containing the TM.

RESULTS

Enzymatically active and inactive tPA (either produced after TM transfection or after direct administration) were equally effective in attenuating steroid-induced outflow facility reduction in C57BL/6J mice. They were also equally effective in rescuing outflow reduction in PlatKO mice and causing enhanced expression of matrix metalloproteinases. However, both enzymatically active and enzymatically inactive tPA did not improve outflow reduction in Mmp-9KO mice or increase the baseline outflow facility in naïve C57BL/6J mice.

CONCLUSIONS

tPA enzymatic activity is not necessary in the regulation of aqueous humor outflow. tPA can increase the expression of matrix metalloproteinases in a cytokine-mediated fashion. This cascade of events may eventually lead to extracellular matrix remodeling at the TM, which reverses outflow facility reduction caused by steroids.

Tissue plasminogen activator attenuates outflow facility reduction in mouse model of juvenile open angle glaucoma

Tissue plasminogen activator (tPA) has been shown to prevent steroid-induced reduction in aqueous humor outflow facility via an upregulation in matrix metalloproteinase (Mmp) expression. The purpose of this study was to determine whether tPA can rescue outflow facility reduction in the Tg-MYOC^Y437H mouse model, which replicates human juvenile open angle glaucoma. Outflow facility was measured in Tg-MYOC^Y437H mice following: periocular steroid exposure and intraocular protein treatment with enzymatically active or enzymatically inactive tPA. Effects of tPA on outflow facility were compared to those of animals treated with topical sodium phenylbutarate (PBA), a modulator of endoplasmic reticulum stress. Gene expression of fibrinolytic pathway components (Plat, Plau, and Pai-1) and matrix metalloproteinases (Mmp-2, -9, and -13) was determined in angle ring tissues containing the trabecular meshwork. Tg-MYOC^Y437H mice did not display further outflow facility reduction following steroid exposure. Enzymatically active and enzymatically inactive tPA were equally effective in attenuating outflow facility reduction in Tg-MYOC^Y437H mice and caused enhanced expression of matrix metalloproteinases (Mmp-9 and Mmp-13). tPA was equally effective to topical PBA treatment in ameliorating outflow facility reduction in Tg-MYOC^Y437H mice. Both treatments were associated with an upregulation in Mmp-9 expression while tPA also upregulated Mmp-13 expression. tPA increases the expression of matrix metalloproteinases and may cause extracellular matrix remodeling at the trabecular meshwork, which results in reversal of outflow facility reduction in Tg-MYOC^Y437H mice.

A Biomimetic, Stem Cell-Derived In Vitro Ocular Outflow Model

Age-related human trabecular meshwork (HTM) cell loss is suggested to affect its ability to regulate aqueous humor outflow in the eye. In addition, disease-related HTM cell loss is suggested to lead to elevated intraocular pressure in glaucoma. Induced pluripotent stem cell (iPSC)-derived trabecular meshwork (TM) cells are promising autologous cell sources that can be used to restore the declining TM cell population and function. Previously, an in vitro HTM model is bioengineered for understanding HTM cell biology and screening of pharmacological or biological agents that affect trabecular outflow facility. In this study, it is demonstrated that human iPSC-derived TM cells cultured on SU-8 scaffolds exhibit HTM-like cell morphology, extracellular matrix deposition, and drug responsiveness to dexamethasone treatment. These findings suggest that iPSC-derived TM cells behave like primary HTM cells and can thus serve as reproducible and scalable cell sources when using this in vitro system for glaucoma drug screening and further understanding of outflow pathway physiology, leading to personalized medicine.

A bioengineering approach to Schlemm's canal-like stem cell differentiation for in vitro glaucoma drug screening

Human Schlemm's canal (HSC) cells are critical for understanding outflow physiology and glaucoma etiology. However, primary donor cells frequently used in research are difficult to isolate. HSC cells exhibit both vascular and lymphatic markers. Human adipose-derived stem cells (ADSCs) represent a potential source of HSC due to their capacity to differentiate into both vascular and lymphatic endothelial cells, via VEGF-A and VEGF-C. Shear stress plays a critical role in maintaining HSC integrity, function, and PROX1 expression. Additionally, the human trabecular meshwork (HTM) microenvironment could provide cues for HSC-like differentiation. We hypothesize that subjecting ADSCs to VEGF-A or VEGF-C, shear stress, and co-culture with HTM cells could provide biological, mechanical, and cellular cues necessary for HSC-like differentiation. To test this hypothesis, effects of VEGF-A, VEGF-C, and shear stress on ADSC differentiation were examined and compared to primary HSC cells in terms of cell morphology, and HSC marker expression using qPCR, immunoblotting, and immunocytochemistry analysis. Furthermore, the effect of co-culture with HTM cells on porous scaffolds on ADSC differentiation was studied. Treatment with VEGF-C under shear stress is effective in differentiating ADSCs into PROX1-expressing HSC-like cells. Co-culture with HTM cells on porous scaffolds leads to HTM/ADSC-derived HSC-like constructs that regulate through-flow and respond as expected to dexamethasone. STATEMENT OF SIGNIFICANCE: We successfully generated human Schlemm's canal (HSC) like cells from adipocyte-derived stem cells induced by biochemical and biomechanical cues as well as bioengineered human trabecular meshwork (HTM) on micropatterned, porous SU8 scaffolds. These stem cell-derived HSC-like cells co-cultured with HTM cells on SU8 scaffolds can regulate through-flow, and in particular, are responsive to steroid treatment as expected. These findings show that ADSC-derived HSC-like cells have the potential to recreate the ocular outflow pathway for in vitro glaucoma drug screening. To the best of our knowledge, it is the very first time to demonstrate derivation of Schlemm's canal-like cells from stem cells. It provides an important alternative source to primary Schlemm's canal cells that are very difficult to be isolated and cultured from human donors.

Do epigenetic changes caused by commensal microbiota contribute to development of ocular disease? A review of evidence

There is evidence that genetic polymorphisms and environmentally induced epigenetic changes play an important role in modifying disease risk. The commensal microbiota has the ability to affect the cellular environment throughout the body without requiring direct contact; for example, through the generation of a pro-inflammatory state. In this review, we discuss evidence that dysbiosis in intestinal, pharyngeal, oral, and ocular microbiome can lead to epigenetic reprogramming and inflammation making the host more susceptible to ocular disease such as autoimmune uveitis, age-related macular degeneration, and open angle glaucoma. Several mechanisms of action have been proposed to explain how changes to commensal microbiota contribute to these diseases. This is an evolving field that has potentially significant implications in the management of these conditions especially from a public health perspective.

Investigations on the Role of the Fibrinolytic Pathway on Outflow Facility Regulation

Purpose

To understand the role and further dissect pathways downstream of tissue plasminogen activator (tPA) and the fibrinolytic pathway in modulating outflow facility.

Methods

Outflow facility of tissue plasminogen activator (Plat) knockout (KO) mice was determined and compared to that of wild-type (WT) littermates. Gene expression of urokinase plasminogen activator (Plau), plasminogen activator inhibitor (Pai-1), plasminogen (Plg), and matrix metalloproteinases (Mmp-2, -9, and -13) was measured in angle tissues. Expression of the same genes and outflow facility were measured in KO and WT mice treated with triamcinolone acetonide (TA). Amiloride was used to inhibit urokinase plasminogen activator (uPA) in Plat KO mice, and outflow facility was measured.

Results

Plat deletion resulted in outflow facility reduction and decreased Mmp-9 expression in angle tissues. Plasminogen expression was undetectable in both KO and WT mice. TA led to further reduction in outflow facility and decreases in expression of Plau and Mmp-13 in plat KO mice. Amiloride inhibition of uPA activity prevented the TA-induced outflow facility reduction in Plat KO mice.

Conclusions

tPA deficiency reduced outflow facility in mice and was associated with reduced MMP expression. The mechanism of action of tPA is unlikely to involve plasminogen activation. tPA is not the only mediator of TA-induced outflow facility change, as TA caused reduction in outflow facility of Plat KO mice. uPA did not substitute for tPA in outflow facility regulation but abrogated the effect of TA in the absence of tPA, suggesting a complex role of components of the fibrinolytic system in outflow regulation.

Prospective Study of Oral Health and Risk of Primary Open-Angle Glaucoma in Men: Data from the Health Professionals Follow-up Study

PURPOSE

Tooth loss or periodontal disease is associated with systemic endothelial dysfunction, which has been implicated in primary open-angle glaucoma (POAG). The relationship between oral health and POAG has received limited attention. Thus, we evaluated the association between oral health history and risk of POAG and POAG subtypes.

DESIGN

Prospective cohort study.

PARTICIPANTS

Health Professionals Follow-up Study participants (40 536 men) followed biennially from 1986 to 2012. At each 2-year risk period, eligible participants were aged 40+ years, were free of POAG, and reported eye examinations.

METHODS

By using validated questions, we updated participants' status on number of natural teeth, teeth lost, periodontal disease with bone loss, and root canal treatments.

MAIN OUTCOME MEASURES

During follow-up, 485 incident cases of POAG were confirmed with medical records and classified into subtypes defined by intraocular pressure (IOP; ≥ or <22 mmHg) or visual field (VF) loss pattern at diagnosis (peripheral loss only or early paracentral loss). Multivariable relative risks (MVRRs) and 95% confidence intervals (CIs) were estimated.

RESULTS

Number of natural teeth, periodontal disease, and root canal treatment were not associated with POAG. However, compared with no report of tooth loss, a report of losing teeth within the past 2 years was associated with a 1.45-fold increased risk of POAG (95% CI, 1.06-1.97); in particular, a report within the past 2 years of both losing teeth and having a prevalent diagnosis of periodontal disease was associated with a 1.85-fold increased risk of POAG (95% CI, 1.07-3.18). The associations with recent tooth loss were not significantly different for the POAG subtypes (P for heterogeneity ≥0.36), although associations were strongest in relation to the POAG subtypes with IOP <22 mmHg (MVRR, 1.93; 95% CI, 1.09-3.43) and early paracentral VF loss (MVRR, 2.27; 95% CI, 1.32-3.88).

CONCLUSIONS

Although the number of natural teeth was not associated with risk of POAG, recent tooth loss was associated with an increased risk of POAG. Because these findings may be due to chance, they need confirmation in larger studies.

Model systems for the study of steroid-induced IOP elevation

Steroid-induced IOP elevation affects a significant number of patients. It results from a decrease in outflow facility of the aqueous humor. To understand the pathophysiology of this condition a number of model systems have been created. These include ex-vivo cell and organ cultures as well as in-vivo animal models in organisms ranging from rodents to primates. These model systems can be used to investigate specific aspects of steroid-induced IOP elevation. This brief review summarizes the strengths and limitations of the various model systems and provides examples of where these systems have been successfully used to advance our understanding of steroid-induced IOP elevation.

Bioengineered glaucomatous 3D human trabecular meshwork as an in vitro disease model

Intraocular pressure (IOP) is mostly regulated by aqueous humor outflow through the human trabecular meshwork (HTM) and represents the only modifiable risk factor of glaucoma. The lack of IOP-modulating therapeutics that targets HTM underscores the need of engineering HTM for understanding the outflow physiology and glaucoma pathology in vitro. Using a 3D HTM model that allows for regulation of outflow in response to a pharmacologic steroid, a fibrotic state has been induced resembling that of glaucomatous HTM. This disease model exhibits HTM marker expression, ECM overproduction, impaired HTM cell phagocytic activity and outflow resistance, which represent characteristics found in steroid-induced glaucoma. In particular, steroid-induced ECM alterations in the glaucomatous model can be modified by a ROCK inhibitor. Altogether, this work presents a novel in vitro disease model that allows for physiological and pathological studies pertaining to regulating outflow, leading to improved understanding of steroid-induced glaucoma and accelerated discovery of new therapeutic targets. Biotechnol. Bioeng. 2016;113: 1357-1368. © 2015 Wiley Periodicals, Inc.

Differential Effects of C1qa Ablation on Glaucomatous Damage in Two Sexes in DBA/2NNia Mice

PURPOSE

To determine the sex and age-related effects of C1qa ablation on retinal ganglion cell (RGC) and optic nerve (ON) axonal loss in a mouse model of glaucomatous neurodegeneration.

METHODS

Congenic C1qa mice were generated in the DBA/2NNia background. Female and male knockout (-/-), heterozygous (+/-), and wild type (+/+) mice were aged up to 14 months and IOPs were recorded in a subset of animals. Retinas of mice from all three groups at 5-6, 9-10 and 11-13 months of age were flat-mounted after retrograde labeling with Fluorogold. Imaged retinas were scored (RGC score) semi-quantitatively on a 10 point scale by two independent observers. A subset of retinas and optic nerves were also used for measurement of total number of RGCs. Semi-thin sections of ON were imaged and graded (ON score) for the amount of axonal damage semi-quantitatively, by two masked observers. Analysis of covariance (ANCOVA) was used for statistical comparisons. Microglial cells in flat-mounted retinas of 5-6 month old C1qa -/- and C1qa +/+ mice were used for assessment of microglial activation utilizing morphological criteria.

RESULTS

Female C1qa -/- mice had significantly higher IOP (p<0.000001, ANOVA) between 8 and 13 months of age compared to C1qa +/+ animals. No differences in IOPs between animals of the three genotypes were observed in males. At 5-6 months of age, there was no difference in RGC or ON scores between the three genotypes in animals of either sex. At 9-10 months of age, female mice didn't show significant differences in RGC or ON scores between the three genotypes. However, male C1qa -/- and C1qa +/- mice of the same age had better RGC and ON scores (p<0.003 and p<0.05, ANCOVA, for RGC and ON scores, respectively) compared with C1qa +/+ mice. At 11-13 months of age, female C1qa -/- mice had better RGC scores (p<0.006, ANCOVA) compared to C1qa +/+ and C1qa +/- animals. Accordingly, C1qa -/- mice had higher RGC counts (p<0.03, t-test) compared to C1qa +/+ animals. In male mice, there was a tendency for 12 month old C1qa -/- animals to have better RGC scores and higher RGC counts, but this didn't reach statistical significance. ON scores in 11-13 month old animals of either sex were not different between all three genotype. Microglial activation in male 5-6 month old C1qa -/- mice was decreased compared to C1qa +/+ animals; no such effect was seen in females.

CONCLUSIONS

Absence of C1qa ameliorates RGC and ON loss in the DBA/2NNia strain, but this effect differs between the two sexes. C1q-mediated RGC damage seems to be more potent than IOP-mediated RGC loss. In contrast, C1qa absence provides axonal protection early on, but this protection cannot overcome the effects of significant IOP elevation.

Retinal projections in the short-tailed fruit bat, Carollia perspicillata, as studied using the axonal transport of cholera toxin B subunit: Comparison with mouse

To provide a modern description of the Chiropteran visual system, the subcortical retinal projections were studied in the short-tailed fruit bat, Carollia perspicillata, using the anterograde transport of eye-injected cholera toxin B subunit, supplemented by the silver-impregnation of anterograde degeneration following eye removal, and compared with the retinal projections of the mouse. The retinal projections were heavily labeled by the transported toxin in both species. Almost all components of the murine retinal projection are present in Carollia in varying degrees of prominence and laterality. The projections: to the superior colliculus, accessory optic nuclei, and nucleus of the optic tract are predominantly or exclusively contralateral; to the dorsal lateral geniculate nucleus and posterior pretectal nucleus are predominantly contralateral; to the ventral lateral geniculate nucleus, intergeniculate leaflet, and olivary pretectal nucleus have a substantial ipsilateral component; and to the suprachiasmatic nucleus are symmetrically bilateral. The retinal projection in Carollia is surprisingly reduced at the anterior end of the dorsal lateral geniculate and superior colliculus, suggestive of a paucity of the relevant ganglion cells in the ventrotemporal retina. In the superior colliculus, in which the superficial gray layer is very thin, the projection is patchy in places where the layer is locally absent. Except for a posteriorly located lateral terminal nucleus, the other accessory optic nuclei are diminutive in Carollia, as is the nucleus of the optic tract. In both species the cholera toxin labeled sparse groups of apparently terminating axons in numerous regions not listed above. A question of their significance is discussed.

Can Visual Field Progression be Predicted by Confocal Scanning Laser Ophthalmoscopic Imaging of the Optic Nerve Head in Glaucoma? (An American Ophthalmological Society Thesis)

PURPOSE

To determine whether confocal scanning laser ophthalmoscopic imaging (Heidelberg retinal tomography [HRT]) can predict visual field change in glaucoma.

METHODS

The study included 561 patients with glaucoma or ocular hypertension whose clinical course was followed at the Mount Sinai Faculty practice. Humphrey visual fields (HVFs) and HRT images were collected on one randomly selected eye per patient. Glaucoma progression was determined by the presence of two sequential statistically significant negative slopes in mean deviation (MD) or visual field index (VFI) at any point during the study period. Trend-based analysis on HRT parameters was used to determine progressive changes and whether these occurred before or after HVF change. Sensitivity and specificity of HRT to predict HVF change were calculated. HVF rate of change was correlated to the rate of change detected by HRT imaging.

RESULTS

Approximately 17% of patients progressed by either MD or VFI criteria. MD and VFI correlated highly and identified overlapping sets of patients as progressing. HRT global parameters had poor sensitivity (∼42%) and moderate specificity (∼67%) to predict HVF progression. Regional stereometric parameters were more sensitive (69%-78%) but significantly less specific (24%-27%). Sensitivity of global stereometric parameters in detecting HVF change was not significantly affected by the level of visual field damage (P=.3, Fisher exact test). HVF rate of change did not correlate with rate of change of HRT parameters.

CONCLUSIONS

Trend-based analysis of HRT parameters has poor sensitivity and specificity in predicting HVF change. This may be related specifically to HRT imaging or may reflect the fact that in some patients with glaucoma, functional changes precede structural alterations.

Tissue plasminogen activator reduces the elevated intraocular pressure induced by prednisolone in sheep

We have previously shown that tissue plasminogen activator (tPA) injected in the vitreous of sheep, reduced or prevented the elevation of the intraocular pressure (IOP) normally produced by the instillation of 1% prednisolone. We now report the effect of tPA when injected into the anterior chamber (AC) in amounts of 0.01, 0.001 and 0.0001 μg diluted in a volume of 50 μL. Lyophilized tPA, obtained as Actilyse 50 mg from Boehringer Ingelheim containing arginine was utilized. The Actilyse was diluted in balanced salt solution to obtain the desired amount of tPA in 50 μL. An identical solution containing only arginine was prepared to inject into the contralateral eye as a control. Six sheep of the Corriedale breed were selected. At the beginning of the study all eyes received instillation of 1% prednisolone 3 times/day for 10 days to elevate their IOP from 10 mm Hg to about 23 mm Hg. Then, 0.0001 μg was injected into one of the eyes and its effect was followed for up to 55:00 h while the instillation of prednisolone continued in both eyes. The same protocol was implemented for the 0.001 and 0.01 μg amounts after extended washout and IOP was over 22 mm Hg. The injection of 0.0001 μg into the AC had no effect on an IOP of 23.0 mm Hg at 6:00 and 30:00 h after injection. 0.001 μg of tPA reduced IOP from 23.1 to 18.6 mm Hg at 6:00 h but IOP recovered to 22.3 mm Hg at 30:00 h. Injection of 0.01 μg produced a marked and prolonged reduction of IOP. From a baseline of 23.0, IOP was reduced to 14.0, 14.7, 21.2, and 20.9 mm Hg at 5.0, 23.0, 27.0 and 45.5 h, respectively. The 0.423 μg of arginine, which is associated with 0.01 μg tPA, was injected alone and had no effect. Recombinant human tPA injected in the AC is effective in reversing steroid-induced IOP elevation in sheep. The reduction of IOP elevation may be the result of an effect on extra-cellular matrix turnover in the TM. These findings suggest that tPA may by useful as a therapeutic agent in steroid-induced glaucomas.

Oral microbiome link to neurodegeneration in glaucoma

BACKGROUND

Glaucoma is a progressive optic nerve degenerative disease that often leads to blindness. Local inflammatory responses are implicated in the pathology of glaucoma. Although inflammatory episodes outside the CNS, such as those due to acute systemic infections, have been linked to central neurodegeneration, they do not appear to be relevant to glaucoma. Based on clinical observations, we hypothesized that chronic subclinical peripheral inflammation contributes to neurodegeneration in glaucoma.

METHODS

Mouthwash specimens from patients with glaucoma and control subjects were analyzed for the amount of bacteria. To determine a possible pathogenic mechanism, low-dose subcutaneous lipopolysaccharide (LPS) was administered in two separate animal models of glaucoma. Glaucomatous neurodegeneration was assessed in the retina and optic nerve two months later. Changes in gene expression of toll-like receptor 4 (TLR4) signaling pathway and complement as well as changes in microglial numbers and morphology were analyzed in the retina and optic nerve. The effect of pharmacologic blockade of TLR4 with naloxone was determined.

FINDINGS

Patients with glaucoma had higher bacterial oral counts compared to control subjects (p<0.017). Low-dose LPS administration in glaucoma animal models resulted in enhancement of axonal degeneration and neuronal loss. Microglial activation in the optic nerve and retina as well as upregulation of TLR4 signaling and complement system were observed. Pharmacologic blockade of TLR4 partially ameliorated the enhanced damage.

CONCLUSIONS

The above findings suggest that the oral microbiome contributes to glaucoma pathophysiology. A plausible mechanism by which increased bacterial loads can lead to neurodegeneration is provided by experiments in animal models of the disease and involves activation of microglia in the retina and optic nerve, mediated through TLR4 signaling and complement upregulation. The finding that commensal bacteria may play a role in the development and/or progression of glaucomatous pathology may also be relevant to other chronic neurodegenerative disorders.

Complement expression in the retina is not influenced by short-term pressure elevation

PURPOSE

To determine whether short-term pressure elevation affects complement gene expression in the retina in vitro and in vivo.

METHODS

Muller cell (TR-MUL5) cultures and organotypic retinal cultures from adult mice and monkeys were subjected to either 24-h or 72-h of pressure at 0, 15, 30, and 45 mmHg above ambient. C57BL/6 mice were subjected to microbead-induced intraocular pressure (IOP) elevation for 7 days. RNA and protein were extracted and used for analysis of expression levels of complement component genes and complement component 1, q subcomponent (C1q) and complement factor H (CFH) immunoblotting.

RESULTS

mRNA levels of complement genes and C1q protein levels in Muller cell cultures remained the same for all pressure levels after exposure for either 24 or 72 h. In primate and murine organotypic cultures, pressure elevation did not produce changes in complement gene expression or C1q and CFH protein levels at either the 24-h or 72-h time points. Pressure-related glial fibrillary acidic protein (GFAP) mRNA expression changes were detected in primate retinal organotypic cultures (analysis of variance [ANOVA]; p<0.05). mRNA expression of several other genes changed as a result of time in culture. Eyes subjected to microbead-induced IOP elevation had no differences in mRNA expression of complement genes and C1q protein levels (ANOVA; p>0.05 for both) with contralateral control and naïve control eyes.

CONCLUSIONS

Short-term elevation of pressure in vitro as well as short-term (1 week) IOP elevation in vivo does not seem to dramatically alter complement system gene expression in the retina. Prolonged expression to elevated pressure may be necessary to affect the complement system expression.

Reduction of steroid-induced intraocular pressure elevation in sheep by tissue plasminogen activator

PURPOSE

To investigate whether tissue plasminogen activator (tPA) can prevent and/or reverse steroid-induced IOP elevation in an ovine model.

METHODS

Three animal groups were subjected to bilateral steroid-induced IOP elevation using thrice daily topical ocular prednisolone administration. In the first group (N = 8), one eye each of two sheep was injected intravitreally with 100 μg, 200 μg, 500 μg, or 1 mg human recombinant tPA, while contralateral eyes received vehicle. In the second group (N = 2), one eye was injected intravitreally with tPA (100 μg), while contralateral eyes received vehicle containing L-arginine. In the third group (N = 4), each animal received intravitreal tPA in one eye concurrently with initiation of bilateral steroid administration. IOP was monitored for the duration of the experiment. Tissues from eyes of the third group were used to determine relative gene expression.

RESULTS

In the first and second groups, IOP decreased by 9.7 (±2.8) and 9.7 (±1.6) mm Hg, respectively, 24 hours after tPA administration. In the third group, tPA-treated eyes did not develop IOP elevation with ΔIOP of 11.8 (±1.3) mm Hg 8 days later. In all tPA-treated eyes, IOP remained low until the end of the study. mRNA levels in the trabecular meshwork were decreased for plasminogen activator tissue (PLAT), increased for matrix-metalloproteinase 1 (MMP-1), and stable for plasminogen activator inhibitor 1 (PAI-1), MMP-2, MMP-9, and MMP-13 in tPA-treated eyes compared with contralateral controls. PAI-1 mRNA levels in ciliary processes also remained similar.

CONCLUSIONS

Recombinant human tPA is effective in both preventing and reversing steroid-induced IOP elevation in sheep. Tissue plasminogen activator may be useful as a therapeutic agent in steroid-induced glaucoma.

Tissue plasminogen activator in trabecular meshwork attenuates steroid induced outflow resistance in mice

Tissue plasminogen activator, a serine protease encoded by the PLAT gene is present in the trabecular meshwork (TM) and other ocular tissues and has been reported to be downregulated by treatment with steroids in vitro. Steroids are known to cause changes in outflow facility of aqueous humor in many species. In the present study, we tested whether overexpression of PLAT can prevent and/or reverse the outflow facility of mouse eyes treated with steroids. Animals received bilateral injection with 20 µl of triamcinolone acetonide (TA) (40 mg/ml) suspension subconjunctivally to induce outflow facility changes. Some animals received unilateral intracameral injection with 2 µl of adenoviral suspension [3-4 x 10(12) virus genomes per milliliter (vg/ml)] carrying sheep PLAT cDNA (AdPLAT) either concurrently with TA injection or one week after TA injection, whereas others received bilateral intracameral injection with 2 µl of adenoviral suspension (9 x 10(12) vg/ml) carrying no transgene (AdNull) concurrently with TA injection. Animals were sacrificed one week after AdPLAT or AdNull treatment. Endogenous mRNA expression levels of mouse PAI-1 and MMP-2, -9 and -13 were also measured using qRT-PCR. Outflow facility one week after AdPLAT administration was increased by 60% and 63% respectively for animals that had not or had been pretreated with steroids. Overexpression of PLAT significantly upregulated expression of PAI-1, MMP-2, -9 and -13 compared to the levels found in TA only treated eyes. These findings suggest that overexpression of PLAT in TM of mouse eyes can both prevent and reverse the decrease in outflow facility caused by steroid treatment and is associated with upregulation of MMPs.

Recreating a human trabecular meshwork outflow system on microfabricated porous structures

Glaucoma is the leading cause of irreversible blindness, resulting from an increase in intraocular pressure (IOP). IOP is the only modifiable risk factor of glaucoma and is controlled by the outflow of the aqueous humor through the human trabecular meshwork (HTM). Currently, the lack of a proper in vitro HTM model impedes advances in understanding outflow physiology and discovering effective IOP-lowering anti-glaucoma therapeutics. Therefore, we designed and constructed an in vitro HTM model using micropatterned, porous SU-8 scaffolds, which support cells to recapitulate functional HTM morphology and allow the study of outflow physiology. The pore size of SU-8 scaffolds, surface coating, cell seeding density, and culture duration were evaluated for HTM cell growth. The bioengineered HTM was characterized by F-actin staining and immunocytochemistry of HTM markers. A stand-alone perfusion chamber with an integrated pressure sensing system was further constructed and used for the investigation of the outflow facility of the bioengineered HTM treated with latrunculin B-an IOP lowering agent. Cells in the in vitro model exhibited HTM-like morphology, expression of α-smooth muscle actin, myocilin, and αß-crystallin, outflow characteristics and drug responsiveness. Altogether, we have developed an in vitro HTM model system for understanding HTM cell biology and screening of pharmacological or biological agents that affect trabecular outflow facility, expediting discovery of IOP-lowering, anti-glaucoma therapeutics.

Triamcinolone acetonide decreases outflow facility in C57BL/6 mouse eyes

PURPOSE

To determine the effect of triamcinolone acetonide (TA) on outflow facility in mice.

METHODS

Animals received 20 μL of TA (40 mg/mL) suspension subconjunctivally either bilaterally or unilaterally and were euthanized after either 1 week or 3 weeks. Before mice were killed, IOP was measured with a rebound tonometer. Outflow facility was determined using simultaneous pressure and flow measurements. Another set of animals received bilateral injection of anecortave acetate (AA) with or without bilateral TA injection and their outflow facility was also determined. Myocilin expression was investigated in a subset of eyes using quantitative PCR (qPCR).

RESULTS

Outflow facility of eyes in animals receiving bilateral TA injection (TA(BL)) and TA-treated eyes of animals receiving unilateral injection (TA(UL)) was significantly decreased compared to naïve control eyes (C(naive)) after 1 week and 3 weeks of TA treatment (ANOVA P < 0.01, P < 0.001, respectively). Eyes treated with AA (with or without TA) had higher outflow facility than animals treated with TA (P < 0.05). IOP data did not show any significant difference between groups. qPCR analysis revealed significant decrease in myocilin expression in eyes receiving AA compared to naïve control and TA-treated eyes (ANOVA P < 0.001).

CONCLUSIONS

Steroid treatment significantly decreases outflow facility in C57BL/6 mice despite having small effect on IOP. This animal model can be useful for studying the pathogenesis of steroid-induced glaucoma.

Effect of axonal micro-tubules on the morphology of retinal nerve fibers studied by second-harmonic generation

Many studies suggest that the degradation of microtubules in the retinal ganglion cells may be an early event in the progression of glaucoma. Because reflectance and birefringence of the retinal nerve fibers arise primarily from microtubules, the optical properties have been intensively studied for early detection of the disease. We previously reported a novel nonlinear optical signal from axonal microtubules for visualizing the retinal nerve fibers, namely second-harmonic generation (SHG). We demonstrate the use of axonal SHG to investigate the effect of microtubules on the morphology of the retinal nerve fiber bundles. Time-lapse SHG imaging of ex vivo rat retinal flat mounts was performed during pharmacological treatment of nocodazole, and the intensity of axonal SHG and the changes in nerve fiber bundle morphology were monitored. We found that the microtubule disruption does not lead to immediate modification in the morphology of the nerve fibers. Our results indicate that microtubular SHG may provide a useful means for sensitive detection of axonal injuries. Since the intrinsic radiation depends on the regular architecture of the cytoskeleton element as maintained by active cellular regulations, the intensity of signal reflects the health of the retinal ganglion cell axons.

Pseudoexfoliation syndrome, a systemic disorder with ocular manifestations

Pseudoexfoliation syndrome (PXS) is a systemic condition with eye manifestations. In the eye, pseudoexfoliation material deposits on various structures of the anterior segment. The nature of this material is mostly fibrillar with fibers made up of microfibrils and coated with amorphous material. The composition of these fibrils is diverse and includes basement membrane components as well as enzymes involved in extracellular matrix maintenance. Pseudoexfoliation is the most common cause of secondary open-angle glaucoma (pseudoexfoliation glaucoma, PXG) worldwide. The goal of this review is to summarize our knowledge on the genetics of this systemic disorder and its resultant ocular manifestations. PXS familial aggregation suggests genetic inheritance. PXS has been strongly associated with single nucleotide polymorphisms (SNPs) of the lysyl oxidase-like 1 (LOXL1) gene on chromosome 15q24.1. Two of these SNPs confer a higher than 99% population attributable risk for PXS and PXG in the Nordic population; however, they carry different risks in different populations. The high risk haplotypes also vary among different populations. LOXL1 is one of group of the enzymes involved in the cross-linking of collagen and elastin in the extracellular matrix. Its function in connective tissue maintenance has been confirmed in mice; however, its actual role in PXS remains unclear. Contactin-associated protein-like 2 also has a strong genetic association with PXS in a German cohort and is an attractive candidate molecule. It encodes for a protein involved in potassium channel trafficking. Other candidate genes linked to PXS include lysosomal trafficking regulator, clusterin, adenosine receptors, matrix metalloproteinase-1 (MMP1), and glutathione transferase. These genes may be modifying genes for development of PXS and PXG.

Label-free morphometry of retinal nerve fiber bundles by second-harmonic-generation microscopy

We present an application of second-harmonic generation (SHG) microscopy for label-free visualization and quantification of the morphology of nerve fibers in the retina. We show that SHG arises from the retinal nerve fiber layer and that it is specifically associated with uniformly oriented microtubules in the axons. The utility of axonal SHG is demonstrated for imaging the neuroanatomy of fresh ex vivo retina, and the three-dimensional structure of the axons of retinal ganglion cells is quantitatively analyzed.

Gene expression changes in steroid-induced IOP elevation in bovine trabecular meshwork

PURPOSE

To determine whether gene expression changes occur in the trabecular meshwork (TM) of cow eyes with steroid-induced intraocular pressure (IOP) elevation.

METHODS

Adult female Braford cows (n = 4) were subjected to uniocular prednisolone acetate treatment for 6 weeks. IOP was monitored with an applanation tonometer. At the conclusion of the experiment, animals were euthanized, eyes were enucleated, and the TM was dissected and stored in an aqueous nontoxic tissue storage reagent. RNA was extracted and subjected to microarray analysis using commercial oligonucleotide bovine arrays. Some of the genes differentially expressed between control and experimental eyes were confirmed by quantitative RT-PCR and some of the respective proteins were studied by immunoblotting.

RESULTS

IOP began to increase after 3 weeks of treatment, reaching a peak 2 weeks later. IOP differences between corticosteroid-treated and fellow control eyes were 6 ± 1 mm Hg (mean ± SD) at the conclusion of the study. Microarray analysis revealed that expression of 258 genes was upregulated, whereas expression of 187 genes was downregulated in the TM of eyes with steroid-induced IOP elevation. Genes identified to be differentially expressed include genes coding for cytoskeletal proteins, enzymes, growth and transcription factors, as well as extracellular matrix proteins and immune response proteins. A number of relevant gene networks were detected by bioinformatic analysis.

CONCLUSIONS

Steroid-induced IOP elevation alters gene expression in the bovine TM. Identification of genes with changing expression in this model of open-angle glaucoma may help elucidate the primary changes occurring at the molecular level in this condition.

Retinal gene expression changes related to IOP exposure and axonal loss in DBA/2J mice

PURPOSE

To determine the effects of cumulative IOP exposure and axonal damage on retinal gene expression in DBA/2 mice.

METHODS

DBA/2J, DBA/2J(pe) (pearl), and C57BL/6 mice from 3 to 12 months of age were used. IOP was measured with a rebound tonometer, and optic nerve (ON) damage was determined by grading of ON sections. Retinal RNA was subjected to microarray analysis. Comparisons explored the effects of cumulative IOP exposure (cIOPx) as well as ON damage (ONd) in the DBA/2J animals compared with that in the C57BL/6 and pearl mice. RT-PCR was performed to confirm some of the genes and bioinformatic analysis to identify affected gene networks.

RESULTS

Microarrays revealed that an increasing number of genes were up- or downregulated in 9- and 12-month DBA/2J mice with various degrees of ONd. A smaller number of genes were expressed differentially between eyes with different cIOPx at the same age, from 6 months on. Expression of 1385 and 1133 genes differed between DBA/2J animals and C57BL/6 or pearl mice, respectively, and some them were confirmed by RT-PCR. Bioinformatics analysis identified functional gene networks, including members of the complement system, that appeared to be related to cIOPx, ONd, or both.

CONCLUSIONS

Gene expression changes occur in retinas of DBA/2 mice with various amounts of cIOPx as well as ONd. Genes involved, code for proteins with diverse cellular functions and include among others the complement system. cIOPx and ONd affect common as well as unique gene sets.

Intraoperative floppy iris syndrome: report of a case and histopathologic analysis

OBJECTIVE

To understand the role of the α(1A)-adrenoreceptors (ARs) in the pathophysiologic mechanism of intraoperative floppy iris syndrome (IFIS).

METHODS

Iris specimens from a patient with tamsulosin hydrochloride-induced IFIS were obtained during trabeculectomy. Specimens underwent histological analysis and immunohistochemical analysis with antibodies specific for actin, myoglobin, α(1A)-ARs, and myosin. Iris specimens from a patient without IFIS were used for comparison. Samples were processed for transmission electron microscopy.

RESULTS

Histological examination showed normal dilator muscle, arterioles, stroma, and pigment epithelium. Actin, myosin, and myoglobin distribution and intensities were similar between IFIS and non-IFIS tissue. The staining pattern and colocalization with myosin suggested that α(1A)-ARs are present in iris arteriolar muscularis in addition to the dilator muscle in both IFIS and control irides. Significantly less staining of IFIS tissue was found compared with the non-IFIS iris. Ultrastructures of melanocytes and stroma appeared to be normal. Iris arterioles possessed thick endothelial basement membranes, semilongitudinally oriented muscularis, and abundant perivascular collagen coats.

CONCLUSIONS

We confirm the presence of α(1A)-ARs in human iris by results of immunohistochemical analysis. The α(1A)-ARs localize to iris arteriolar muscularis in addition to the iris dilator muscle. This localization suggests that IFIS may develop because of iris vascular dysfunction and that iris vasculature may have structural in addition to nutritive functions.

Morphologic changes in the outflow pathways of bovine eyes treated with corticosteroids

PURPOSE

To analyze morphologic changes in the trabecular meshwork (TM) of bovine eyes treated with topical prednisolone and exhibiting elevated intraocular pressure for 4 weeks.

METHODS

The TM of four adult Braford cow eyes treated with 0.5% prednisolone eye drops three times daily for 7 weeks and their contralateral eyes treated with artificial tear preparation and that of two adult untreated Braford cows and untreated young calves eyes were analyzed with light and electron microscopy. Increased extracellular matrix (ECM) under the outflow loops was evaluated quantitatively. Additionally, deparaffinized tissue of treated eyes was labeled with an antibody against type VI collagen for immunocytochemistry.

RESULTS

In steroid-treated eyes ECM (plaques) accumulated under the endothelium of the inner wall of the outflow loops. On electron microscopy, this material contained fine fibrils that labeled for type VI collagen. Plaques were also seen in the contralateral controls of the treated animals but here they were significantly less in amount. In the untreated Braford controls and in untreated calf eyes, plaques were nearly absent. In the TM cells of the treated eyes there was a loss of glycogen from the cytoplasm and an increase in basement membrane-like material. These changes were not seen in contralateral eyes or eyes of untreated animals.

CONCLUSIONS

Accumulations of ECM in the treated eyes resembled morphologic changes in human eyes with primary open-angle glaucoma and steroid-induced glaucoma. This animal model, therefore, provides a good tool in which to further study the pathogenesis of TM changes in glaucoma.

Gene expression changes in areas of focal loss of retinal ganglion cells in the retina of DBA/2J mice

Purpose. To determine whether differences in gene expression occur between areas of focal retinal ganglion cell (RGC) loss and of relative RGC preservation in the DBA/2 mouse retina and whether they can provide insight into the pathophysiology of glaucoma. Methods. Areas of focal RGC loss (judged by lack of Fluorogold labeling; Fluorochrome, Denver, CO), adjacent areas with relative RGC preservation in DBA/2 retina, and Fluorogold-labeled retina from DBA/2(-pe) (pearl) mice were dissected and used for microarray analysis. RT-PCR and immunoblot analysis were used to confirm differential gene expression. Bioinformatic analysis was used to identify gene networks affected in the glaucomatous retina. Results. Microarray analysis identified 372 and 115 gene chip IDs as up- and downregulated, respectively, by 0.5-fold in areas of RGC loss. Differentially expressed genes included those coding for cytoskeletal proteins, enzymes, transport proteins, extracellular matrix (ECM) proteins, and immune response proteins. Several genes were confirmed by RT-PCR. For at least two genes, differential protein expression was verified. Bioinformatics analysis identified multiple affected functional gene networks. Pearl mice appeared to have significantly different gene expression, even when compared with relatively preserved areas of the DBA/2 retina. Conclusions. Regional gene expression changes occur in areas of focal RGC loss in the DBA/2 retina. The genes involved code for proteins with diverse cellular functions. Further investigation is needed to determine the cellular localization of the expression of these genes during the development of spontaneous glaucoma in the DBA/2 mouse and to determine whether some of these gene expression changes are causative or protective of RGC loss.

Steroid-induced ocular hypertension in normal sheep

PURPOSE

To determine whether the ovine eye develops elevation of intraocular pressure (IOP) in response to corticosteroid applied topically.

METHODS

IOP was monitored by Perkins applanation tonometry in a group of 18 sheep receiving topically administered 0.5% prednisolone acetate in one eye (experimental), three times daily, for a period of 3 or four 4 weeks after the establishment of baseline IOP values. Perkins readings were converted to actual mm Hg using a calibration curve derived from in vivo manometric measurements. IOP was monitored for an additional 1 to 3 weeks after discontinuation of corticosteroid treatment.

RESULTS

Baseline IOP in normal sheep was 10.6+/-1.4 mm Hg (mean +/- SD; n=36 eyes). The IOP of the experimental eyes began to increase after 1 week of prednisolone treatment in all sheep and reached a peak 1 week later (27.5 mm Hg experimental vs. 11.7 mm Hg fellow, control eye; P<0.001). After the discontinuation of corticosteroid instillation, the IOP of the treated eyes declined to the baseline values over the course of 1 to 3 weeks.

CONCLUSIONS

Ovine eyes exhibit a robust steroid-induced ocular hypertensive response, with 100% occurrence in this trial. The mechanisms of steroid-induced glaucoma may be related to those involved in primary open-angle glaucoma and could provide insight into primary open-angle and clues to its treatment.

Comparison of anterior segment structures in two rat glaucoma models: an ultrasound biomicroscopic study

PURPOSE

Optic nerve disease in chronic IOP elevation rat glaucoma models develops at different rates. This study was undertaken to investigate whether anterior chamber (AC) changes develop in two popular models in vivo and whether the changes are related to IOP.

METHODS

Ten female Wistar rats and 12 male Brown-Norway rats were subjected to episcleral vein cauterization (EVC) and hypertonic saline episcleral vein sclerosis (HSEVS), respectively. Contralateral untreated eyes served as controls. IOP was recorded for a period of 5 to 6 weeks, and with the rats under anesthesia, the eyes were imaged with an ultrasound biomicroscope. Measurements of the AC depth (ACD), trabecular-iris angle (TIA), iris thickness at the thickest point near the pupillary margin (IT), angle opening distance (AOD; at 200 microm from the scleral spur), and ciliary body area (CBA) were compared between control eyes of the two strains and between experimental and control eyes within each strain. The differences were correlated with IOP history.

RESULTS

Eyes subjected to EVC demonstrated greater increases in IOP than eyes subjected to HSEVS. Between rat strains, control eyes differed significantly in all the parameters studied, except for ACD. No difference was detected between experimental and control eyes in the EVC group. In contrast, experimental eyes in the HSEVS group had approximately 71% larger ACDs and approximately 32% smaller CBAs than did the contralateral control eyes (P < 0.001). ACD and CBA correlated well (R2 = 0.80 and 0.51, respectively) with IOP in the HSEVS group. Two of the experimental eyes in this group showed the presence of ultrasound-scattering material in the AC.

CONCLUSIONS

Despite apparently higher IOP exposure, eyes in the EVC rat model of glaucoma do not undergo changes in the AC. In contrast, eyes subjected to HSEVS display deepening of the AC and reduction in size of the ciliary body within 5 to 6 weeks. These changes correlate to IOP exposure and may be the result of specific changes induced by the experimental intervention. These models are likely to rely on different mechanisms of pressure elevation and cannot be used interchangeably.

Ceruloplasmin Upregulation in Retina of Murine and Human Glaucomatous Eyes

PURPOSE

Ceruloplasmin (Cp) expression is increased locally as a response to many neurodegenerative conditions. The purposes of this study were to confirm findings of Cp upregulation in glaucoma, detect the time course of this upregulation in a glaucoma model, and better localize its expression in the retina.

METHODS

mRNA and protein were extracted from the retina and brain of DBA/2 and C57BL/6 mice and were subjected to analysis by RT-PCR and immunoblotting. In addition, eyes from the same mouse strains were subjected to immunohistochemistry using antibodies specific for Cp. Eyes from human subjects with or without glaucoma were also subjected to immunohistochemical analysis for Cp.

RESULTS

Cp mRNA and Cp protein were upregulated in the retinas of glaucomatous DBA/2 mice. Upregulation of Cp occurred at approximately the time of extensive retinal ganglion cell (RGC) death and increased with increasing age to 15 months in the retinas but not in the brains of these animals. No age-related Cp upregulation was detected in the reference normal mouse strain (C57BL/6), which can develop significant nonglaucomatous RGC loss toward the end of the same time frame. Cp upregulation was also detected in most eyes from the patients with glaucoma. Cp upregulation was localized to the Müller cells within the retinas and in the area of the inner limiting membrane.

CONCLUSIONS

Cp is upregulated in the retina of a commonly used glaucoma model (the DBA/2 mouse) and in most human glaucomatous eyes. The timing of this upregulation suggests that it may represent a reactive change of the retina in response to a noxious stimulus or to RGC death. Such Cp upregulation may represent a protective mechanism within the retina.

Noninvasive Determination of Intraocular Pressure (IOP) in Nonsedated Mice of 5 Different Inbred Strains

BACKGROUND

Noninvasive intraocular pressure (IOP) measurement in mice is critically important for understanding the pathophysiology of glaucoma. Rebound tonometry is one of the methods that can be used for obtaining such measurements. We evaluated the ability of the rebound tonometer (RT) to determine IOP differences among various mouse strains and whether differences in corneal thickness may affect IOP measurements in these animals.

MATERIALS AND METHODS

Five different commonly used mouse strains (BALB/C, CBA/CAHN, AKR/J, CBA/J, and 129P3/J) were used. IOP was measured in eyes from 12 nonsedated animals (6 male and 6 female) from each strain at 2 to 3 months of age using the RT. IOPs were measured in all animals, on 2 different days between 10 AM and 12 PM. Subsequently, a number of eyes from each strain were cannulated to provide a calibration curve specific for that strain. Tonometer readings for all strains were converted to apparent IOP values using the calibration data obtained from the calibration curve of the respective strain. For comparison purposes, IOP values were also obtained using the C57BL/6 calibration data previously reported. IOP for the 5 strains, male and female animals, and the different occasion of measurement were compared using repeat measures analysis of variance. The central corneal thickness (CCT) of another group of 8 male animals from each of the 5 strains was also measured using an optical low coherence reflectometry (OLCR) pachymeter modified for use with mice. CCT values were correlated to mean IOPs of male animals and to the slopes and intercept of individual strain calibration curves.

RESULTS

Noninvasive IOP measurements confirm that the BALB/C strain has lower and the CBA/CAHN has higher relative IOPs than other mouse strains while the AKR/J, the CBA/J, and the 129P3/J strains have intermediate IOPs. There is a very good correlation of apparent IOP values obtained by RT with previously reported true IOPs obtained by cannulation. There was a small but statistically significant difference in IOP between male and female animals in 2 strains (129P3/J and AKR/J) with female mice having higher relative IOPs. No correlation between CCT and IOP was detected. CCT did not correlate with any of the constants describing the calibration curves in the various strains.

CONCLUSIONS

Noninvasive IOP measurement in mice using the RT can be used to help elucidate IOP phenotype, after prior calibration of the tonometer. CCT has no effect on mouse IOP measurements using the RT.

Apoptotic retinal ganglion cell death in the DBA/2 mouse model of glaucoma

The DBA/2 mouse has been used as a model for spontaneous secondary glaucoma. We attempted to determine the in vivo time course and spatial distribution of retinal ganglion cells (RGCs) undergoing apoptotic death in DBA/2 mice. Female DBA/2 mice, 3, 9-10, 12, 15, and 18 months of age, received intravitreal injections of Annexin-V conjugated to AlexaFluor 1h prior to euthanasia. Retinas were fixed and flat-mounted. Annexin-V-positive RGCs in the hemiretina opposite the site of injection were counted, and their locations were recorded. Positive controls for detection of apoptotic RGCs by Annexin-V labeling included rats subjected to optic nerve ligation, and C57BL/6 mice subjected to either optic nerve ligation or intravitreal injection of NMDA. To verify that Annexin-V-labeled cells were RGCs, intravitreal Annexin-V injections were also performed on retinas pre-labeled retrogradely with FluoroGold or with DiI. Annexin-V-positive RGC locations were analyzed to determine possible clustering and areas of preferential loss. Annexin-V labeled apoptotic RGCs in eyes after optic nerve ligation, intravitreal NMDA injection, as well as in aged DBA/2 animals. In glaucomatous DBA/2 mice 95-100% of cells labeled with Annexin-V were also FluoroGold- and DiI-positive. This confirms that Annexin-V can be used to specifically detect apoptotic RGCs in rodent retinas. In DBA/2 mice, apoptotic RGC death is maximal from the 12th to the 15th month of age (ANOVA, p<0.001, Fisher's post hoc test) and occurs in clusters. These clusters are initially located in the midperipheral retina and progressively occur closer to the optic nerve head with increasing age. Retrograde axonal transport of FluoroGold in the glaucomatous mouse retina is functional until at least 2-3days prior to initiation of apoptotic RGC death.

Predictability and limitations of non-invasive murine tonometry: Comparison of two devices

Our purpose was to evaluate the accuracy, reproducibility and predictive ability of two non-invasive tonometers developed for intraocular pressure (IOP) measurements in the mouse. The prototype impact-rebound tonometer (I-R) and a prototype optical interferometry tonometer (OIT) utilizing a fiberoptic pressure sensor, were compared. Enucleated eyes from C57/BL6 mice were used for the calibration. The anterior chamber was cannulated and the IOP was adjusted in increments of 5 cm of H2O (open stopcock method). A calibration curve was generated for each individual eye along with a master calibration curve for all eyes. Two operators measured the IOP. The instruments were then used in alternating order to measure the IOP in C57/BL6 and in DBA2/J animals. The same eyes were subsequently cannulated and the error of the non-invasive tonometers was determined. Both tonometers yielded almost equivalent ex vivo calibration curves with individual R2 of 0.9878 and 0.9902 respectively. Both instruments were highly reproducible. In vivo the I-R tonometer underestimated while the OIT overestimated the IOP. This error was systematic and therefore predictable. The confidence intervals of this error were determined by comparing the IOP estimates provided by each tonometer with the measurements obtained invasively by cannulation in vivo. The 95% CI of the error were 2.36 mmHg for the I-R and 2.62 mmHg for the OIT respectively. Non-invasive tonometry in the mouse is feasible. Both non-invasive instruments provide accurate and reproducible measurements with the OIT requiring calibration curves for each individual investigator.

Photodynamic treatment in a rabbit model of glaucoma surgery

PURPOSE

To evaluate the safety and efficacy of postoperative verteporfin photodynamic treatment as an adjunct to glaucoma experimental filtration surgery in rabbits.

METHODS

Dutch belted (n = 15) rabbits underwent full thickness sclerectomy in one eye. The experimental group (group 1, n = 7) underwent i.v. injection of verteporfin and subsequent photoactivation at the operative site on postoperative day 1 (POD 1). Control groups of animals received either light exposure (group 2, n = 4) or verteporfin (group 3, n = 2), or no intervention (group 4, n = 2). Intraocular pressure (IOP) was measured prior to the procedure (POD 0) and daily thereafter for the first week after sclerectomy (PODs 1-7) and every other day for the second week (PODs 9, 11, 13, 15). Percentage IOP reductions of operated over contralateral control eyes were compared among the various groups. Success rates (percentage IOP reduction > 15%) were also compared between the experimental and control groups. Eyes were histologically examined for evaluation of fibrosis.

RESULTS

Rabbits in the experimental group (group 1) had a mean +/- SEM percentage IOP reduction of 25 +/- 3% during the follow-up period. In contrast, groups 2, 3 and 4 had IOP reductions of 4 +/- 5%, 12 +/- 7% and 4 +/- 6%, respectively (p < 0.005, anova among all four groups). Successful IOP reduction (> or = 15%) over the contralateral eye at POD 15 was achieved in six of seven experimental animals, but only in one of eight control animals (p < 0.02, chi-squared test). Bleb failure occurred significantly earlier in the control eyes compared with eyes receiving PDT (p < 0.003, log rank test). Blebs in the experimental group differed from those in the control groups histologically, lacking significant collagen deposition in the area of the sclerostomy.

CONCLUSIONS

Wound healing in glaucoma surgery may be successfully modulated postoperatively using photodynamic therapy with i.v. administered photosensitizer.

Topographic and Morphologic Analyses of Retinal Ganglion Cell Loss in Old DBA/2NNia Mice

PURPOSE

To evaluate the relationship between retinal ganglion cell (RGC) size, density distribution, and survival in senescent DBA2/NNia mice that develop pigmentary glaucoma. To evaluate the validity of nearest neighbor distance (NND), a measure of focal density for surviving RGCs in the retina, as a method to quantify RGC loss in mice.

METHODS

Fifteen-month-old DBA2/NNia mice were labeled retrogradely with fluorogold. Retinas were flat mounted and imaged in their entirety using an epifluorescence microscope with a motorized stage. Digital maps of the retinal wholemounts were constructed to automatically count and establish spatial coordinates for RGCs over the entire retina. RGC size and NND were determined from these maps.

RESULTS

RGC counts in the group of 15-month-old DBA/2NNia animals ranged from 22,330 to 92,157 cells per retina. Mean RGC cell size per retina ranged from 22.35 to 35.64 microm2 and correlated linearly with total RGC counts. NND distribution histograms were compared for retinas with variable degrees of RGC loss. The distribution of NNDs in each retina was skewed toward larger distance values in more affected retinas. In partially damaged retinas, areas with severe pathology coincided with areas of maximal loss of large RGCs, and areas of preserved RGCs correlated with larger cell sizes.

CONCLUSIONS

Damaged retinas have a smaller mean cell size, indicating preferential loss of larger RGCs or size reduction of surviving cells. NND analysis of the RGC population in a retina is a useful measure of glaucomatous RGC loss. The skewed NND distribution of surviving RGCs and the finding that RGC loss correlates with a shift/amplitude change in the mode of the histogram and its tail suggests two different patterns of RGC loss possibly attributable to different pathologic processes in glaucomatous DBA/2 mice.

Complement Component 1Q (C1Q) Upregulation in Retina of Murine, Primate, and Human Glaucomatous Eyes

PURPOSE

Complement has been implicated in the pathogenesis of neurodegenerative diseases. The purpose of this study was to investigate whether complement activation is part of the pathogenesis of retinal ganglion cell (RGC) loss in glaucoma.

METHODS

mRNA and protein was extracted from the retina and brain of DBA/2 and C57/BL6 mice and subjected to RT-PCR and immunoblot analysis, respectively. In addition, eyes from the same mouse strains were subjected to immunohistochemistry with antibodies specific to complement component 1q (C1q). Eyes from monkeys with unilateral experimental glaucoma were also subjected to immunohistochemical analysis, as were eyes from human subjects with or without glaucoma.

RESULTS

C1q mRNA and C1q protein were found to be upregulated in the retina of glaucomatous DBA/2 mice. Upregulation of C1q preceded the time of extensive RGC death and increased with increasing age to 15 months in the retina, but not in the brain. No age-related C1q upregulation was detected in the reference mouse strain (C57BL/6), which develops significant nonglaucomatous RGC loss toward the end of the same time frame. C1q upregulation was also detected in laser-induced glaucomatous monkey eyes and in some (but not all) eyes of patients with glaucoma. C1q upregulation was localized to the Müller cells within the retina and in the area of the inner limiting membrane.

CONCLUSIONS

Complement expression is upregulated in the retina of two commonly used glaucoma models (in the DBA/2 mouse and the monkey) and in some human glaucomatous eyes. The timing of this upregulation suggests that complement activation plays a significant role in the pathogenesis of glaucoma.

Comparison of invasive and non-invasive tonometry in the mouse

Assessment of the accuracy of non-invasive rebound tonometry, and comparison with invasive cannulation tonometry. An in vivo calibration technique was devised to improve the accuracy of the rebound tonometer. IOP was then measured in SW mice using both rebound and cannulation tonometry. The ability of the rebound tonometer to accurately measure small IOP reductions after instillation of a topical prostaglandin was also determined. With the rebound method, mid-afternoon IOP in two groups of similar aged SW mice was 15.9+/-3.9 mmHg (mean+/-s.d., n=25) compared to 16.3+/-1.2 mmHg (n=32) using the cannulation technique. This difference was not statistically significant (p=0.6). For serial measurements using both techniques in the same eyes of a third group of SW mice (n=14), mean IOP was 15.0+/-3.9 mmHg for rebound tonometry but only 13.4+/-2.3 mmHg for subsequent cannulation tonometry. This effect was subsequently shown to be a consequence of the rebound tonometry, as multiple rebound measurements induced a statistically significant reduction in IOP. The average IOP reduction observed 2 hr after a single application of topical latanoprost (200 ng) was 2.8+/-1.3 mmHg (p<0.001) and 2.4+/-4.7 mmHg (p=0.03) with cannulation and rebound tonometers, respectively. These differences were not significantly different (p=0.8). In vivo calibration of the rebound tonometer increased measurement accuracy and provided IOP values within the physiological range that agreed closely with the IOP measured by cannulation tonometry. However, IOP measurement with the rebound tonometer had larger variability compared with the cannulation method. Repeat IOP measurements with the rebound tonometer led to a reduction in IOP. The rebound tonometer was sufficiently sensitive to detect a 2-3 mmHg reduction in IOP following application of topical latanoprost. Despite these limitations, the rebound tonometer has a significant advantage over cannulation tonometry in that it permits longitudinal IOP measurement in conscious mice.

Is intraocular pressure in the early postoperative period predictive of antimetabolite-augmented filtration surgery success?

PURPOSE

To determine whether intraocular pressure (IOP) in the early postoperative period after trabeculectomy or combined phacoemulsification-trabeculectomy, augmented with antimetabolite, correlates with IOP at one year in surgeries considered to be successful at that time point.

DESIGN

Retrospective case series.

METHODS

A chart review of antimetabolite-augmented surgical procedures done by DJG and JBS between January 1994 and November 2000 identified 82 primary or secondary trabeculectomies and 53 combined phacoemulsification-trabeculectomies with at least one year of follow-up. The success rate for each surgical subgroup was calculated and IOP on postoperative days (POD +/- SD) 1, 7 (+/-2), 30 (+/-5), 90 (+/-10), and 180 (+/-20) was correlated with IOP at one year (POY 1, between month 12 and 15) using linear regression. IOP at each time point was compared among eyes that achieved success at one year with and without the use of IOP-lowering agents.

RESULTS

Of the 82 eyes having undergone antimetabolite-augmented trabeculectomies and the 53 eyes having undergone combined surgeries with at least one year of follow-up, the surgical success rates at POY 1 were 87.8% (72 of 82 eyes) and 92.5% (49 of 53 eyes). Of these, 42 eyes (58.3%) from 39 patients in the trabeculectomy group and 27 eyes (55.1%) from 24 patients in the combined surgery group did not require glaucoma medications at one year postsurgically, and were considered complete surgical successes. Mean preoperative IOP mm Hg +/- SD was 26.0 +/- 8.5 for the trabeculectomy group and 18.2 +/- 4.5 for the phaco-trabeculectomy group. Postoperative IOP at POD 1, POD 7, POD 30, POD 90, POD 180, and POY 1 respectively for the eyes undergoing trabeculectomy were 13.9 +/- 10.4, 9.5 +/- 6.2, 12.0 +/- 5.5, 12.0 +/- 5.2, 12.8 +/- 5.9, and 12.1 +/- 4.3, and for the combined surgery group were 20.8 +/- 12.5, 9.7 +/- 5.7, 12.2 +/- 5.4, 11.1 +/- 3.4, 11.6 +/- 4.6, and 10.3 +/- 4.3. Intraocular pressure on postoperative day one correlated poorly with intraocular pressure at POY 1 for the trabeculectomy group (R2 = 0.0788), and not at all for the combined procedures group (R2 = 0.018). The correlation was slightly better for intraocular pressure at postoperative day 90 for the trabeculectomy group (R2 = 0.546), and at postoperative day 180 for the combined group (R2 = 0.37), but still rather low. Eyes requiring glaucoma medication use at POY 1 in the trabeculectomy group had higher (P < 0.009) intraocular pressure at POD 30 and at all subsequent visits than eyes not requiring these medications. Eyes requiring glaucoma medication use at POY 1 in the phaco-trabeculectomy group had higher (P < 0.0025) intraocular pressure at POD 30, POD 180, and POY 1 than eyes not requiring these medications.

CONCLUSION

Intraocular pressure in the early postoperative period correlates very poorly with intraocular pressure one year after successful antimetabolite-augmented trabeculectomy or combined cataract extraction and trabeculectomy. Starting one month after glaucoma surgery, intraocular pressure is substantially lower in eyes that will ultimately not require the use of ocular hypotensive agents to achieve clinical success one year postoperatively.

Characterization of retinal damage in the episcleral vein cauterization rat glaucoma model

Episcleral vein cauterization (EVC) is used in rats to generate a glaucoma model with high intraocular pressure (IOP). The long-term retinal damage in this glaucoma model, however, has not been accurately quantified. We report the location and amount of retinal ganglion cell (RGC) damage caused by (EVC) induced IOP elevation in two rat strains. IOP was raised in one eye of Wistar (N = 5) and Brown-Norway(B-N)(N = 7) rats by EVC and monitored monthly until IOP in contralateral eyes equalized at 5 months post-surgery. Animals were maintained for 3.5-4.5 additional months. B-N rats (N = 7) that had no EVC served as controls for this strain. Scotopic flash ERGs were recorded at baseline and just prior to euthanasia. Automated counts of all retrogradely labeled RGCs in retinal flat-mounts were determined and compared between contralateral eyes. RGC density maps were constructed and RGC size distribution was determined. Oscillatory potentials in the group of eyes which had elevated IOP were decreased at the time of euthanasia, when IOP had returned to normal. The group of normal B-N rats had similar RGC counts between contralateral eyes. In the experimental group the mean number of RGCs was not significantly different between control and experimental eyes, but 1 of 5 Wistar and 2 of 7 B-N experimental eyes had at least 30% fewer RGCs than contralateral control eyes. Total retinal area in B-N experimental eyes was higher compared to contralateral eyes. Cumulative IOP exposure of the experimental eyes was modestly correlated with RGC loss while oscillatory potentials appeared to be inversely related to RGC loss. In retinas with extensive (> 30% RGC loss) but not complete damage, smaller cells were preserved better than larger ones. The above results indicate that RGC loss in both Wistar and B-N strains is variable after a prolonged elevation of IOP via EVC. Such variability despite equivalent IOP levels and ERG abnormalities, suggests unknown factors that can protect IOP-stressed RGCs. Identification and enhancement of such factors could prove useful for glaucoma therapy.

Ultrasound biomicroscopy of the rat eye: effects of cholinergic and anticholinergic agents

BACKGROUND

Over the past few years the rat has gained prominence as an animal model for the study of glaucoma. However, no systematic study of the angle structures and the effects of medications on angle anatomy in the rat has been reported to date. We investigated the normal rat anterior segment anatomy in vivo using ultrasound biomicroscopy (UBM) and determined the effect of both cholinergic and anticholinergic medications on angle structures.

METHODS

Fourteen eyes of seven 2-month-old female Wistar rats were imaged using an ultrasound biomicroscope and a modified eyecup. Baseline measurements of the anterior chamber depth (ACD), trabecular-iris angle (TIA), iris thickness at the thickest point near the pupillary margin (IT), angle-opening distance (AOD) (distance between the posterior corneal surface and anterior iris surface measured at 200 microm from the scleral spur), corneal thickness (CT) and irido-zonular distance (IZD) were obtained. Imaging was repeated 30 min after instillation of one drop of cyclopentolate 1% and 48 h later 30 min after pilocarpine 1% instillation. The same measurements were obtained and compared to baseline values.

RESULTS

Baseline values for all parameters recorded were not significantly different among contralateral eyes. After instillation of either pilocarpine or cyclopentolate, ACD was the only parameter that did not change significantly from baseline. In contrast, TIA, AOD, IZD, and IT were significantly different among the three groups. Post-hoc analysis (Bonferroni test) revealed differences among all three groups of eyes for TIA and AOD. A difference was also found between the pilocarpine-treated group and the other two groups for IZD and IT. A very small difference detected between the pilocarpine-treated group and the baseline measurements for CT was caused by the zero variance of measurements in the former group. Although both pilocarpine and cyclopentolate induced angle narrowing, inspection of the ultrasonic images revealed a differential effect. Pilocarpine caused a "pupillary block-like" picture, while cyclopentolate caused crowding of the iris base in the angle.

CONCLUSIONS

Baseline characteristics of the normal rat anterior chamber anatomy were established. Both cyclopentolate and pilocarpine cause angle narrowing in the rat eye, by different mechanisms.