Presence of a contractile cell network in the human choroid

The structure and function of the human choroid

In this manuscript, the structure of the human choroid is reviewed with emphasis of the macro- and microscopic anatomy including Bruch's membrane, choriocapillaris, Sattler's and Haller's layer, and the suprachoroid. We here discuss the development of the choroid, as well as the question of choroidal lymphatics, and further the neuronal control of this tissue, as well as the pathologic angiogenesis. Wherever possible, functional aspects of the various structures are included and reviewed.

[Anatomo-functional state of the central retina in premature infants with intraventricular hemorrhage and retinopathy of prematurity]

OBJECTIVE

Assessment of the anatomo-functional state of the central retina in children with intraventricular hemorrhage (IVH) and retinopathy of prematurity (ROP) in the long-term period.

MATERIAL AND METHODS

We examined 51 patients (102 eyes) born 25-34 weeks' of gestation (birth weight 700-2290 g), aged 8.83±3.5 years, and 18 children (36 eyes) born prematurely aged 10.8±3.2 years. The children underwent standard ophthalmologic examination, optical coherence tomography (OCT) and visual evoked potentials (VEP).

RESULTS

Retinal thickness (RT) and retinal volume (RV) in the fovea of premature infants with PH and/or IVH are significantly higher than in healthy full-term infants, which correlates with lower visual acuity (p<0.05). RT and RV in the fovea has an inverse proportional relationship with gestational age (GA), (p<0.05). According to the results of VEP, moderate organic changes in the conduction tract of the visual analyzer are noted in 45% of premature infants (p<0.05).

CONCLUSION

The process of macula formation is affected by many perinatal and postnatal factors, namely: GA, birth weight, ROP, hypoxic-ischemic CNS diseases, and refractive disorders.

The effect of topical 1 % atropine on ocular dimensions and diurnal rhythms of the human eye

The effect of topical 1 % atropine on the diurnal rhythms of the human eye was investigated. Participants wore an activity monitor on Days 1-7. A set of measures (epochs) encompassing intraocular pressure (IOP), ocular biometry, and retinal imaging were obtained on Day 7 (baseline), followed by eight epochs on Day 8, and one on Day 9 from both eyes of healthy participants (n = 22, 19-25 years). The sleep time of participants (collected via actigraphy) was used as a reference in scheduling epochs. Topical 1 % atropine was instilled in the dominant eye on Day 8, 2 h after habitual wake time, using the fellow eye as control (paired-eye design). Sinusoids with a 24-h period were fitted to the data, and a non-linear mixed-effects model was used to estimate rhythmic statistics. There were no interocular differences in any of the measured parameters at baseline. Comparing pre- versus post-atropine in treated eyes revealed lower IOP, deeper anterior chamber (ACD), decreased crystalline lens thickness and shorter axial length (AL). The same trends were observed when comparing atropine-treated versus fellow control eyes, except for IOP and AL (no differences). Both atropine-treated and fellow control eyes showed significant diurnal variations in all ocular parameters, with atropine-treated eyes revealing larger AL and retinal thickness amplitudes, smaller vitreous chamber depth (VCD) amplitudes, and a significant phase advancement for ACD and VCD. There were no interocular differences in choroidal thickness rhythms. In conclusion, while ocular diurnal rhythms persisted after instillation of 1 % atropine, many rhythmic parameters were altered.

Choroidal Morphology and Systemic Circulation Changes During the Menstrual Cycle in Healthy Japanese Women

PURPOSE

Changes in systemic circulatory dynamics and choroidal thickness are poorly understood. This study aimed to investigate the time course of changes in choroidal morphology during normal menstrual cycles in healthy women using enhanced depth imaging optical coherence tomography (EDI-OCT).

MATERIALS AND METHODS

This prospective study included 15 left eyes of 15 healthy Japanese women (mean age, 20.2 ± 0.8 years) with a normal menstrual cycle. Using EDI-OCT, the subfoveal choroidal thickness (SCT) was manually measured during the late follicular and mid-luteal phases. Intraocular pressure (IOP), systolic, diastolic, and mean blood pressure (SBP, DBP, and MBP), and heart rate (HR) were also evaluated during these phases.

RESULTS

SBP, DBP, and MBP were significantly elevated in the mid-luteal phase. The average SCT was significantly decreased in the mid-luteal phase. In contrast, there were no significant changes in IOP or HR.

CONCLUSION

These findings indicate that choroidal thickness decreases during the mid-luteal phase in healthy Japanese women with normal menstrual cycles depending on systemic circulatory dynamics. However, since the difference in the SCT values between the late follicular and the mid-luteal phase is not large (7 μm), the menstrual cycle may have little influence on the interpretation of choroidal thickness data in clinical practice.

Parasympathetic Dominance Decreases the Choroidal Blood Flow Velocity Measured Using Laser Speckle Flowgraphy

BACKGROUND

This study aimed to examine the changes to choroidal blood flow velocity using laser speckle flowgraphy (LSFG) in healthy eyes after warm water immersion at 40°C.

METHODS

Data regarding the right eyes of 23 healthy volunteers were included. The mean blur rate (MBR) of the macula, which represents the choroidal blood flow velocity, was evaluated using LSFG. Intraocular pressure (IOP), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean blood pressure (MBP), ocular perfusion pressure (OPP), and MBR were assessed at baseline, immediately after immersion (0 minutes), and 10, 20, and 30 minutes later.

RESULTS

At 0 minutes, SBP, DBP, MBP, and OPP values were lower than those at baseline. The MBR significantly declined immediately after immersion to -6.0 ± 5.2%. However, there were no changes in these parameters after 10, 20, or 30 minutes. A significant positive correlation was observed between the MBR, SBP, DBP, MBP, and OPP values. In healthy individuals, the dominant parasympathetic activity induced by warm stimulation reduced the choroidal hemodynamic rate in the macula and decreased systemic circulatory dynamics, which normalized after 10 minutes.

CONCLUSIONS

These findings suggest that the dominant parasympathetic activity induced by warm water immersion at 40°C may lead to a reduction in the systemic circulation rate and choroidal blood flow rate in the macula. These findings may help prevent and treat various retinal choroidal diseases, in which sympathetic hyperactivity is involved in the pathogenesis of the disease.

Uveal vascular bed in health and disease: uveal vascular bed anatomy. Paper 1 of 2

The uveal vascular bed is the largest vascular system in the eye and has a role in supplying almost every tissue in the eyeball. This makes it the most important ocular vascular system. This is an up-to-date review of the literature of the entire uveal vascular bed in health based on detailed anatomy of the posterior ciliary arteries (PCAs), anterior ciliary arteries, cilioretinal arteries, and vortex veins. Although postmortem injection cast preparations gave us useful information on the morphology of the choroidal vascular bed; in vivo studies showed that they misled us for centuries about the in vivo situation. According to the postmortem cast studies, the uveal vascular bed has no segmental distribution, the uveal vessels anastomose freely with one another, there are inter-arterial and arteriovenous anastomoses in the choroid, and the choriocapillaris form a freely communicating and an uninterrupted vascular bed in the entire choroid.

Parasympathetic and sympathetic control of emmetropization in chick

Emmetropization can be altered by temporal visual stimulation and the spectral properties of the visual environment. The goal of the current experiment is to test the hypothesis that there is an interaction between these properties and autonomic innervation. For that purpose, selective lesions of the autonomic nervous system were performed in chickens followed by temporal stimulation. Parasympathetic lesioning involved transection of both the ciliary ganglion and the pterygopalatine ganglion (PPG_CGX; n = 38), while sympathetic lesioning involved transection of the superior cervical ganglion (SCGX; n = 49). After one week of recovery, chicks were then exposed to temporally modulated light (3 days, 2 Hz, Mean: 680 lux) that was either achromatic (with blue [RGB], or without blue [RG]), or chromatic (with blue [B/Y] or without blue [R/G]). Control birds with lesions, or unlesioned, were exposed to white [RGB] or yellow [RG] light. Ocular biometry and refraction (Lenstar and a Hartinger refractometer) was measured before and after exposure to light stimulation. Measurements were statistically analyzed for the effects of a lack of autonomic input and the type of temporal stimulation. In PPG_CGX lesioned eyes, there was no effect of the lesions one-week post-surgery. However, after exposure to achromatic modulation, the lens thickened (with blue) and the choroid thickened (without blue) but there was no effect on axial growth. Chromatic modulation thinned the choroid with R/G. In the SGX lesioned eye, there was no effect of the lesion 1-week post-surgery. However, after exposure to achromatic modulation (without blue), the lens thickened and there was a reduction in vitreous chamber depth and axial length. Chromatic modulation caused a small increase in vitreous chamber depth with R/G. Both autonomic lesion and visual stimulation were necessary to affect the growth of ocular components. The bidirectional responses observed in axial growth and in choroidal changes suggest that autonomic innervation combined with spectral cues from longitudinal chromatic aberration may provide a mechanism for homeostatic control of emmetropization.

Changes in Choroidal Circulation Hemodynamics Measured Using Laser Speckle Flowgraphy after a Cold Pressor Test in Young Healthy Participants

Using laser speckle flowgraphy (LSFG), we investigated the time course of changes in choroidal circulation hemodynamics after a cold pressor test in healthy eyes. This prospective study included the right eye of 19 young healthy participants. The macular mean blur rate (MBR) was measured with LSFG. The MBR, intraocular pressure (IOP), systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), mean blood pressure (MBP), and ocular perfusion pressure (OPP) were evaluated at baseline; immediately after the test and 10, 20, and 30 min later. Immediately after the test (0 min), SBP, DBP, MBP, and OPP were significantly elevated compared with those at baseline. The macular MBR significantly increased by +10.3 ± 7.1% immediately after the test. However, there was no change after 10, 20, and 30 min in the above parameter. A significant positive correlation of the macular MBR with the SBP, MBP, and OPP was observed. In young healthy individuals, increased sympathetic activity induced by a cold pressor test increases choroidal hemodynamics in the macula along with an increase in systemic circulatory dynamics, which normalizes after 10 min. Therefore, LSFG may provide a novel approach for assessing sympathetic activity and intrinsic vascular responsiveness in the eye.

Pressure-Dependent Elevation of Vasoactive Intestinal Peptide Level in Chicken Choroid

PURPOSE

Autonomic control is important in maintaining ocular integrity. As recent data suggested that intrinsic choroidal neurons (ICN), an intrinsic choroidal autonomic control, may regulate choroidal thickening via release of the vasodilative vasoactive intestinal peptide (VIP), it was the aim of the study to investigate the level of choroidal VIP (VIP_chor) in the presence of an increased atmospheric pressure in a chicken model.

METHODS

Chicken choroidal whole mounts were exposed to ambient pressure (n = 20) and 40 mm Hg (n = 20) in a PC-controlled, open chamber system for 24 and 72 h, respectively. The VIP concentration was analyzed by ELISA, and the total protein concentration was measured by the BCA assay. Statistical analysis was done using an unpaired two-tailed t-test.

RESULTS

The pressurization systems enabled choroidal whole mount pressurization (40 mm Hg) with humidifying, pressure, temperature, and gas exchange. Overall, the VIP_chor level concentration was significantly increased at 40 mmHg compared to the ambient pressure (30.09 ± 7.18 pg vs. 20.69 ± 3.24 pg; p < 0.0001). Subgroup analysis yielded a significantly increased VIP_chor level at 40 mmHg compared to the ambient pressure after 24 h (28.42 ± 6.03 pg vs. 20.76 ± 4.06 pg; p = 0.005) and 72 h (31.77 ± 7.82 pg vs. 20.61 ± 2.12 pg; p = 0.002), respectively. The VIP_chor elevation at 40 mm Hg ranged between 1.37- (24 h) and 1.54-fold (72 h) compared to the ambient pressure. No difference was observed between the VIP_chor level at 24 h and 72 h (p > 0.05).

CONCLUSIONS

The increase of the total choroidal VIP level, representing the intracellular VIP content, in the presence of an increased ambient pressure argues for a retention of VIP within the neurons, decreasing both vasodilatation and, consequently, choroid thickness. This finding might be a passive or even active function of ICN in the regulation of choroidal thickness, ocular integrity and IOP.

Targeted surface marker screening on neuronal structures in the human choroid

While choroidal neuronal control is known to be essential for retinal and ocular health, its mechanisms are not understood. Especially, the local choroidal innervation mediated by intrinsic choroidal neurons (ICN) remains enigmatic. Neuronal functionality depends on the synaptic neurotransmitters and neuroregulatory peptides involved as well as from membrane components presented on the cell surface. Since the neuronal surface molecular expression patterns in the choroid are currently unknown, we sought to determine the presence of various cluster-of-differentiation (CD) antigens in choroidal neuronal structures with a particular focus on ICN. Human choroids were prepared for immunohistochemistry and the pan-neuronal marker PGP9.5 was combined with CD15, CD24, CD29, CD34, CD46, CD49b, CD49e, CD56, CD58, CD59, CD71, CD81, CD90, CD146, CD147, CD151, CD165, CD171, CD184, CD200, CD271 and fluorescence- and confocal laser scanning-microscopy was used for documentation. The following antigens were found to be co-localized in PGP.9.5+ nerve fibers and ICN perikarya: CD29, CD34, CD56, CD81, CD90, CD146, CD147, CD151, CD171, CD200 and CD271, while all other CD markers where not detectable. Whereas CD24^- and CD59^- immunoreactivity was clearly absent in ICN perikarya, some neural processes of the choroidal stroma displayed CD24 and CD59 immunopositivity. While a multitude of the aforementioned CD-markers were indeed detected in nervous structures of the choroid, the CD24⁺ and CD59⁺ nerve fibers most likely have extrinsic origin from cranial ganglia since ICN cell bodies were found to lack both markers. These findings illustrate how the detailed analysis of CD molecules described here opens novel avenues for future functional studies on choroidal innervation and its control.

Orbital and ocular perfusion in thyroid eye disease

Thyroid eye disease (TED) is characterized by enlargement of extraocular muscles, an increase in retrobulbar fat, orbital fibrosis, and fluctuations in plasma thyroid hormone levels in most patients, often associated with raised autoantibody titers. The occurrence of orbital space conflict compromises the orbital perfusion, unchecked progression of which results in irreversible loss of visual acuity and visual fields. The quantitative assessment of orbital perfusion can be done by measurement of blood flow velocities in the superior ophthalmic vein (SOV), ophthalmic artery (OA), central retinal artery (CRA), and posterior ciliary artery by color Doppler imaging. The retinal and choroidal microvasculature is studied by optical coherence tomography and optical coherence tomography angiography. The orbital and ocular perfusion fluctuates during the course of TED. Orbital congestion is reflected by the reduction or reversal of SOV flow and an increase in subfoveal choroidal thickness. The active phase is characterized by high blood flow velocities of the OA and CRA. The onset of dysthyroid optic neuropathy is associated with reduced arterial perfusion and reduction in parafoveal and peripapillary vascular density. Orbital decompression improves the SOV flow and decreases the resistivity index of CRA. Sequential evaluation of orbital hemodynamic changes can thus supplement the clinical scoring systems for monitoring and planning intervention in TED.

In Vivo Retinal Pigment Epithelium Imaging using Transscleral Optical Imaging in Healthy Eyes

Objective

To image healthy retinal pigment epithelial (RPE) cells in vivo using Transscleral OPtical Imaging (TOPI) and to analyze statistics of RPE cell features as a function of age, axial length (AL), and eccentricity.

Design

Single-center, exploratory, prospective, and descriptive clinical study.

Participants

Forty-nine eyes (AL: 24.03 ± 0.93 mm; range: 21.9-26.7 mm) from 29 participants aged 21 to 70 years (37.1 ± 13.3 years; 19 men, 10 women).

Methods

Retinal images, including fundus photography and spectral-domain OCT, AL, and refractive error measurements were collected at baseline. For each eye, 6 high-resolution RPE images were acquired using TOPI at different locations, one of them being imaged 5 times to evaluate the repeatability of the method. Follow-up ophthalmic examination was repeated 1 to 3 weeks after TOPI to assess safety. Retinal pigment epithelial images were analyzed with a custom automated software to extract cell parameters. Statistical analysis of the selected high-contrast images included calculation of coefficient of variation (CoV) for each feature at each repetition and Spearman and Mann-Whitney tests to investigate the relationship between cell features and eye and subject characteristics.

Main Outcome Measures

Retinal pigment epithelial cell features: density, area, center-to-center spacing, number of neighbors, circularity, elongation, solidity, and border distance CoV.

Results

Macular RPE cell features were extracted from TOPI images at an eccentricity of 1.6° to 16.3° from the fovea. For each feature, the mean CoV was < 4%. Spearman test showed correlation within RPE cell features. In the perifovea, the region in which images were selected for all participants, longer AL significantly correlated with decreased RPE cell density (R Spearman, Rs = -0.746; P < 0.0001) and increased cell area (Rs = 0.668; P < 0.0001), without morphologic changes. Aging was also significantly correlated with decreased RPE density (Rs = -0.391; P = 0.036) and increased cell area (Rs = 0.454; P = 0.013). Lower circular, less symmetric, more elongated, and larger cells were observed in those > 50 years.

Conclusions

The TOPI technology imaged RPE cells in vivo with a repeatability of < 4% for the CoV and was used to analyze the influence of physiologic factors on RPE cell morphometry in the perifovea of healthy volunteers.

Financial Disclosures

Proprietary or commercial disclosure may be found after the references.

Morphological, Immunohistochemical, and Ultrastructural Studies of the Donkey's Eye with Special Reference to the AFGF and ACE Expression

The donkey is mainly used as a working animal for riding and pack transport, as well as for dairy and meat production. Eye afflictions are common in donkeys, thus requiring a detailed study. A few studies had focused on the donkey's eye, and most of them had considered it, merely, a horse's eye. This study aimed to investigate the anatomy, histology, ultrastructure, and immunohistochemical features of the donkey's eye. The results were recorded and compared to those of horses in certain dimensions. Unlike horses, the donkey's eye is more circular in the contour of the cornea, has smaller lenticular thickness, and has longer anterior and vitreous chambers. Positive immunoreactivity to acidic fibroblast growth factor in the basal cell layers of the cornea was observed, indicating their role in cell differentiation and the renewal of the epithelium. Moreover, the corneal keratocytes expressed angiotensin-converting enzyme, which plays a role in corneal homeostasis and wound healing. Additionally, telocytes, hyalocytes, and other immune cells were observed within the iris and ciliary processes. Hence, this work is an updated detailed study of the morphology and ultrastructure of the donkey's eye and reveals some similarities and dissimilarities to the horse's eyes, which should be considered in clinical practice.

The choroid-sclera interface: An ultrastructural study

Emmetropization is an active and visually guided process that involves the retina, choroid and sclera, and results in compensatory changes in eye growth. This guided growth is the result of visual cues and possibly mechanical interactions being translated into growth signals via molecular events from the retina into the choroid and sclera, through the choroidal scleral transition zone. If mechanical interactions were a part of the choroid-sclera signaling transduction cascade, specific morphological arrangements should be detectable in this region at the ultrastructural level. The goal of this study was to investigate the ultrastructural features of the choroidal scleral transition zone by comparing avian, non-human primate and human eyes, with the goal to confirm whether specific mechanical structures are present. Choroidal and scleral tissue from chicken, marmoset, and human eyes were imaged using transmission electron microscopy to document the choroid-sclera transition zone. In chicken eyes, fibroblast lamellae bordered the scleral matrix and formed thin end elongated processes that were undercut by scleral collagen fibrils. These processes back-looped into the scleral matrix, and displayed small club-like membrane protrusions. Differences in these arrangements in mature vs young chickens were not detected. The club-like membrane protrusions identified in chickens were rare in marmoset eyes, which instead exhibited two types of collagen fibrils discriminated by size, and were absent in the human eyes investigated. In marmoset and human eyes, elastic components were detected in the transition zone that were absent in chickens. In summary, cellular/membrane specializations indicating a mechanical interaction at the choroid-sclera transition zone were not detected in chicken, non-human primate or human eyes. If mechanotransduction is necessary for scleral growth, matrix integrity or development, alternative structural arrangements might be required.

Assessment of Choroidal Vascularity and Choriocapillaris Blood Perfusion After Accommodation in Myopia, Emmetropia, and Hyperopia Groups Among Children

Purpose

To investigate choroidal vascularity (CV) and choriocapillaris blood perfusion before and after accommodation in myopia, emmetropia, and hyperopia groups among children.

Methods

This study included 39 myopic eyes from 22 subjects, 17 emmetropic eyes from 11 subjects, and 18 hyperopic eyes from 10 subjects. All subjects were children. Choroidal thickness (CT) and CV, including total choroidal area (TCA), luminal area (LA), and stromal area (SA) were measured using swept-source optical coherence tomography (SS-OCT). Choriocapillaris luminal area (CLA) was measured using SS-OCT-angiography before and after accommodation (near reading with an additional −3 diopter lens).

Results

For baseline results, except horizontal CV (showing no significant differences between myopia and emmetropia groups), both horizontal and vertical CT and CV were significantly smaller in the myopia group than in the emmetropia or hyperopia groups. In terms of CLA, no significant differences were observed among the myopia, emmetropia, and hyperopia groups. In addition, only myopic eyes showed significant decreases in CT and CV, whereas most CT and CV of emmetropic and hyperopic eyes showed non-significant decreases after accommodation. Furthermore, accommodation induced no significant changes in CLA in the myopia, emmetropia, or hyperopia groups.

Conclusion

Myopia had thinner baseline choroid and lower baseline choroidal blood perfusion. Furthermore, myopic eyes were more prone to choroidal thinning and blood perfusion decreases after accommodation.

[Anatomical, morphological and biomechanical aspects of accommodation]

The article reviews the findings on the anatomy, morphological and biomechanical features of the accommodation apparatus. Modern methods of imaging and biometry confirm the validity of the Helmholtz lenticular theory of accommodation, according to which its mechanism involves three main components: the ciliary body, the zonular fibres and the lens capsule, the lens itself. Based on this, there is certain interest in studying the degree of participation of each of these components in the development of age-related changes in accommodation (presbyopia).

Biomechanical properties of retina and choroid: a comprehensive review of techniques and translational relevance

Studying the biomechanical properties of biological tissue is crucial to improve our understanding of disease pathogenesis. The biomechanical characteristics of the cornea, sclera and the optic nerve head have been well addressed with an extensive literature and an in-depth understanding of their significance whilst, in comparison, knowledge of the retina and choroid is relatively limited. Knowledge of these tissues is important not only to clarify the underlying pathogenesis of a wide variety of retinal and vitreoretinal diseases, including age-related macular degeneration, hereditary retinal dystrophies and vitreoretinal interface diseases but also to optimise the surgical handling of retinal tissues and, potentially, the design and properties of implantable retinal prostheses and subretinal therapies. Our aim with this article is to comprehensively review existing knowledge of the biomechanical properties of retina, internal limiting membrane (ILM) and the Bruch’s membrane–choroidal complex (BMCC), highlighting the potential implications for clinical and surgical practice. Prior to this we review the testing methodologies that have been used both in vitro, and those starting to be used in vivo to aid understanding of their results and significance.

Reverse meridional cyclodialysis ab interno in management of open angle glaucoma — a preliminary report

The uveoscleral outflow as an alternate route of aqueous drainage is of great interest in glaucoma surgical treatment. A cyclodialysis cleft allows one to create a direct connection between the anterior chamber (AC) and the suprachoroidal space (SCS) which is the key element of uveoscleral outflow. The purpose of the study was to evaluate the safety and effectiveness of reverse meridional cyclodialysis ab interno (RMCai) in decreasing intraocular pressure (IOP) in patients with primary open-angle glaucoma (POAG) and refractory glaucoma (RG). Fourteen patients who exhibited POAG and RG (11 men and 3 women, age 77.3 ± 7.8 years) were included in the study. All patients underwent RMCai with the help of custom-designed spatula. The spatula, inserted through a clear corneal incision, was used to detach the ciliary body from the scleral spur to create a 2.0–2.5 mm wide and 6.0–6.5 mm deep cleft. Outcome measures were IOP change, use of hypotensive medication(s), complications, and need for a second surgery. Decrease in IOP by more than 20% and IOP between 6 and 21 mmHg without hypotensive medication constituted complete success. Similar changes in IOP with medication constituted partial success. Need for second surgery constituted failure. The follow-up period was >3 months. Baseline IOP and hypotensive medication use were 22.0 ± 8.5 mmHg (95% confidence interval (CI), 17.6–26.4) and 2.6 ± 0.9 (95% CI, 2.2–3.1). At 3, 6, 12, 18, and 24 months, complete success was achieved in 64.3%, 77.8%, 55.6%, 37.5%, and 40% of patients respectively; partial success — in 14.3%, 22.2%, 44.4%, 50.0%, and 60.0%. Four patients required a second surgery. Failure occurred because of cleft closure by fibrosis. It was concluded that RMCai is safe and effective in decreasing IOP in POAG and RG patients.

IMI - Report on Experimental Models of Emmetropization and Myopia

The results of many studies in a variety of species have significantly advanced our understanding of the role of visual experience and the mechanisms of postnatal eye growth, and the development of myopia. This paper surveys and reviews the major contributions that experimental studies using animal models have made to our thinking about emmetropization and development of myopia. These studies established important concepts informing our knowledge of the visual regulation of eye growth and refractive development and have transformed treatment strategies for myopia. Several major findings have come from studies of experimental animal models. These include the eye's ability to detect the sign of retinal defocus and undergo compensatory growth, the local retinal control of eye growth, regulatory changes in choroidal thickness, and the identification of components in the biochemistry of eye growth leading to the characterization of signal cascades regulating eye growth and refractive state. Several of these findings provided the proofs of concepts that form the scientific basis of new and effective clinical treatments for controlling myopia progression in humans. Experimental animal models continue to provide new insights into the cellular and molecular mechanisms of eye growth control, including the identification of potential new targets for drug development and future treatments needed to stem the increasing prevalence of myopia and the vision-threatening conditions associated with this disease.

Diurnal variation of choriocapillaris vessel flow density in normal subjects measured using optical coherence tomography angiography

Background

Vessel flow density (VFD) may provide important information regarding perfusion status. Diurnal variation in VFD of choriocapillaris has not been reported in literature. In the index study, optical coherence tomography angiography (OCTA) was used to assess the diurnal variation of the VFD in the choriocapillaris of subjects with no known ocular disease.

Methods

Fifty eyes with no known ocular disease (25 subjects) were included. OCTA images were acquired using AngioVue (Optovue, Fremont, CA, USA) at two different time points on a single day: 9:00 AM and 6:00 PM. Macular cube scan protocol (3 × 3 mm) centered on the fovea was used. Automatic segmentation of the retinal layers and choriocapillaris was performed using ReVue software, which was also used to measure the choriocapillaris VFD. Horizontal line scan passing through fovea was obtained by the device at both time points to measure the subfoveal choroidal thickness (CT). Linear measurement tool of software was used to measure subfoveal CT according to a standardized reproducible method. Wilcoxon signed-rank test was used to assess the differences in choriocapillaris VFD and subfoveal CT at the two time points. Correlation between change in choriocapillaris VFD and subfoveal CT at the two time points was assessed using the Pearson correlation coefficient (r).

Results

The mean age of the subjects was 31.96 ± 11.23 years. Choriocapillaris VFD was significantly higher at 9:00 AM compared to 6:00 PM (P < 0.0001) with mean choriocapillaris VFD of 68.74 ± 4.80% at 9:00 AM and 67.57 ± 5.41% at 6:00 PM, with a mean diurnal amplitude of 1.17%. Mean subfoveal CT was 287.74 ± 61.51 µm at 9:00 AM and 270.06 ± 60.73 µm at 6:00 PM. Subfoveal CT was also significantly higher at 9:00 AM compared to 6:00 PM (P < 0.0001) with a mean diurnal amplitude of 17.68 µm. Change in choriocapillaris VFD correlated with change in subfoveal CT (r = 0.87, P < 0.001).

Conclusion

OCTA demonstrated significant diurnal change in choriocapillaris VFD in subjects without any ocular disease with VFD being higher in the morning and lower in the evening. Decrease in choriocapillaris VFD in the evening correlated with a reduction in subfoveal CT.

Peripapillary Choroidal Thickness and Retinal Nerve Fiber Layer in Untreated Patients with Obstructive Sleep Apnea-Hypopnea Syndrome: A Case-Control Study

PURPOSE

To evaluate peripapillary choroidal thickness (PPCT), central macular choroidal thickness (CMCT), and retinal nerve fiber layer (RNFL) thickness in untreated patients with obstructive sleep apnea-hypopnea syndrome (OSAHS).

METHODS

This prospective, randomized, and comparative study was conducted in a university ophthalmology clinic. 106 eyes of 106 patients with OSAHS and 44 eyes of 44 healthy individuals were evaluated in this study. Only right eyes were evaluated. The patients with OSAHS were divided into three groups as mild (group 1), moderate (group 2), and severe (group 3) according to apnea-hypopnea index. The PPCT, CMCT, and RNFL measurements were performed by using spectral domain optical coherence tomography with enhanced depth imaging technique. The main parameters assessed were PPCT-Temporal, PPCT-Superior, PPCT-Nasal, PPCT-Inferior quadrants, CMCT, and RNFL thicknesses.

RESULTS

The PPCT of all quadrants was significantly thicker in the control group compared with the moderate and severe subgroups of OSAHS (p < 0.05). The PPCT-Superior and PPCT-Temporal were significantly thinner in the mild subgroup compared with the control group (p = 0.003 and p = 0.028, respectively). There was no difference between the control and mild groups regarding the RNFL thicknesses except nasal RNFL and inferotemporal RNFL which are thinner in the mild group. The RNFL thicknesses of all quadrants were significantly thicker in the control group compared with moderate and severe subgroups (p < 0.05). The CMCT was significantly thicker in the control group compared with all subgroups of OSAHS (p < 0.05).

CONCLUSIONS

In OSAHS patients, PPCT, CMCT, and RNFL were significantly thinner compared with the control group. These results may explain why OSAHS patients are prone to normotensive glaucoma.

CHOROIDAL THICKNESS IN INFANTS WITH RETINOPATHY OF PREMATURITY

PURPOSE

To evaluate choroidal thickness in premature infants and its relationship with stage of retinopathy of prematurity (ROP) using spectral domain optical coherence tomography (SD-OCT).

METHODS

Spectral domain optical coherence tomography imaging for measuring subfoveal choroidal thickness was performed for 80 premature infants. Subfoveal choroidal thickness was defined as the distance from the hyperreflective line of the outermost retinal pigment epithelium (RPE) to the innermost hyperreflective line of the choroidoscleral junction. Each measurement was performed at the central fovea (CF) and 0.75 mm to 1.5 mm nasal (N1 and N2) and temporal (T1 and T2) to the fovea. Subfoveal choroidal thickness and grading of cystoid macular edema (CME) were analyzed statistically.

RESULTS

Choroidal thickness of CF was found to be significantly greater than nasal (N1 and N2) and temporal (T1 and T2) choroidal thickness (P < 0.05). There was no significant relationship between stage of ROP and nasal (N1 and N2) choroidal thickness (P = 0.057, P = 0.282, respectively). However, CF and temporal (T1 and T2) choroidal thickness was found to be significantly lower at a higher stage of ROP (P = 0.005, P = 0.01 and P = 0.001). No significant relationship was found between subfoveal choroidal thickness and the grades of cystoid macular edema (P > 0.05). The choroidal thickness of CF was found to be correlated with birth weight (r = 0.267, P = 0.017) but not birth week (r = 0.140, P = 0.217). Maximum stage of ROP was found to be negatively correlated with choroidal thickness, at N1, T1, and T2 (r < -0.250, P < 0.02).

CONCLUSION

The subfoveal choroid in premature infants can be effectively evaluated using a portable SD-OCT device. Choroidal thickness gets thinner with the severity of ROP and the decrease is more prominent at the central and temporal location. Cystoid macular edema is not correlated with choroidal thickness in premature infants.

Residual deformations in ocular tissues

Residual deformations strongly influence the local biomechanical environment in a number of connective tissues. The sclera is known to be biomechanically important in healthy and diseased eyes, such as in glaucoma. Here, we study the residual deformations of the sclera, as well as the adjacent choroid and retina. Using freshly harvested porcine eyes, we developed two approaches of quantifying residual deformations in the spherically shaped tissues of interest. The first consisted of punching discs from the posterior wall of the eye and quantifying the changes in the area and eccentricity of these samples. The second consisted of cutting a ring from the equatorial sclera and making stress-relieving cuts in it. Measurements of curvature were made before and after the stress-relieving cuts. Using the first approach, we observed a 42% areal contraction of the choroid, but only modest contractions of the sclera and retina. The observed contractions were asymmetric. In the second approach, we observed an opening of the scleral rings (approx. 10% decrease in curvature). We conclude that residual bending deformations are present in the sclera, which we speculate may be due to radially heterogeneous growth and remodelling of the tissue during normal development. Further, residual areal deformations present in the choroid may be due to the network of elastic fibres in this tissue and residual deformations in the constituent vascular bed. Future studies of ocular biomechanics should attempt to include effects of these residual deformations into mechanical models in order to gain a better understanding of the biomechanics of the ocular wall.

Diurnal variations in blood flow at optic nerve head and choroid in healthy eyes: diurnal variations in blood flow

To investigate the diurnal variations of the ocular blood flow in healthy eyes using laser speckle flowgraphy (LSFG), and to determine the relationship of the diurnal variations between the ocular blood flow and other ocular parameters.This prospective cross-sectional study was conducted at Nagoya University Hospital. We studied 13 healthy volunteers whose mean age was 33.5 ± 7.6 years. The mean blur rate (MBR), expressing the relative blood flow, on the optic nerve head (ONH) and choroidal blood flow was determined by LSFG (LSFG-NAVI) every 3 hours from 6:00 to 24:00 hours. The intraocular pressure (IOP), choroidal thickness measured by enhanced depth imaging optical coherence tomography, systolic (SBP) and diastolic (DBP) blood pressure, and heart rate (HR) in the brachial artery were also recorded. We evaluated the diurnal variations of the parameters and compared the MBR to the other parameters using a linear mixed model.The diurnal variations of the MBR on the ONH varied significantly with a trough at 9:00 hours and a peak at 24:00 hours (P < 0.001, linear mixed model). The MBR of choroid also had significant diurnal variations with a trough at 15:00 hours and a peak at 18:00 hours (P = 0.001). The IOP (P < 0.001), choroidal thickness (P < 0.001), SBP (P = 0.005), DBP (P = 0.001), and HR (P < 0.001) also had significant diurnal variations. Although the diurnal variation of the MBR on the ONH was different from the other parameters, that on the choroid was significantly and positively correlated with the DBP (P = 0.002), mean arterial pressure (P = 0.023), and mean ocular perfusion pressure (P = 0.047).We found significant diurnal variations in the ONH and choroidal blood flow. Although the ONH blood flow had its own diurnal variation because of strong autoregulation, the choroidal blood flow was more likely affected by systemic circulatory factors because of poor autoregulation.

Biomechanics of the Posterior Eye: A Critical Role in Health and Disease

The posterior eye is a complex biomechanical structure. Delicate neural and vascular tissues of the retina, choroid, and optic nerve head that are critical for visual function are subjected to mechanical loading from intraocular pressure, intraocular and extraorbital muscles, and external forces on the eye. The surrounding sclera serves to counteract excessive deformation from these forces and thus to create a stable biomechanical environment for the ocular tissues. Additionally, the eye is a dynamic structure with connective tissue remodeling occurring as a result of aging and pathologies such as glaucoma and myopia. The material properties of these tissues and the distribution of stresses and strains in the posterior eye is an area of active research, relying on a combination of computational modeling, imaging, and biomechanical measurement approaches. Investigators are recognizing the increasing importance of the role of the collagen microstructure in these material properties and are undertaking microstructural measurements to drive microstructurally-informed models of ocular biomechanics. Here, we review notable findings and the consensus understanding on the biomechanics and microstructure of the posterior eye. Results from computational and numerical modeling studies and mechanical testing of ocular tissue are discussed. We conclude with some speculation as to future trends in this field.

Evaluation of subfoveal choroidal thickness in children with type 1 diabetes mellitus: an EDI-OCT study

PURPOSE

To evaluate the subfoveal choroidal thickness (SFCT) measured by enhanced depth imaging optical coherence tomography (EDI-OCT) in children with type 1 diabetes without diabetic retinopathy.

METHODS

In this prospective and comparative study, 41 diabetic children without diabetic retinopathy and 42 age-matched healthy subjects were enrolled. The SFCT was measured by EDI-OCT. Correlations between SFCT and diabetic parameters such as fasting glucose level, HbA1c, age, or duration of diabetes were also evaluated.

RESULTS

The mean SFCT value was 375.3 ± 66.5 μm in the eyes with diabetes and 356.4 ± 52.0 μm in the control group. The SFCT was not correlated with fasting glucose level, HbA1c, age, or duration of diabetes.

CONCLUSION

This study showed that SFCT of diabetic children are similar to those of healthy controls. In addition, SFCT are not affected by fasting glucose level, HbA1c, age, or duration of diabetes.

Identification of RALDH2 as a visually regulated retinoic acid synthesizing enzyme in the chick choroid

PURPOSE

All-trans-retinoic acid (atRA) has been implicated in the local regulation of scleral proteoglycan synthesis in vivo. The purpose of the present study was to identify the enzymes involved in the synthesis of atRA during visually guided ocular growth, the cells involved in modulation of atRA biosynthesis in the choroid, and the effect of choroid-derived atRA on scleral proteoglycan synthesis.

METHODS

Myopia was induced in White leghorn chicks by form deprivation for 10 days, followed by up to 15 days of unrestricted vision (recovery). Expression of atRA synthesizing enzymes was evaluated by semiquantitative qRT-PCR, in situ hybridization, and immunohistochemistry. atRA synthesis was measured in organ cultures of isolated choroids using LC-tandem MS quantification. Scleral proteoglycan synthesis was measured in vitro by the incorporation of (35)SO(4) in CPC-precipitable glycosaminoglycans. RESULTS; RALDH2 was the predominant RALDH transcript in the choroid (> 100-fold that of RALDH3). RALDH2 mRNA was elevated after 12 and 24 hours of recovery (60% and 188%, respectively; P < 0.01). The atRA concentration was significantly higher in cultures of choroids from 24-hour to 15-day recovering eyes than in paired controls (-195%; P < 0.01). Choroid conditioned medium from recovering choroids inhibited proteoglycan synthesis to 43% of controls (P < 0.02, paired t-test; n = 16) and produced a relative inhibition corresponding to a RA concentration of 7.20 × 10(-8) M.

CONCLUSIONS

The results of this study suggest that RALDH2 is the major retinal dehydrogenase in the chick choroid and is responsible for increased atRA synthesis in response to myopic defocus.

The multifunctional choroid

The choroid of the eye is primarily a vascular structure supplying the outer retina. It has several unusual features: It contains large membrane-lined lacunae, which, at least in birds, function as part of the lymphatic drainage of the eye and which can change their volume dramatically, thereby changing the thickness of the choroid as much as four-fold over a few days (much less in primates). It contains non-vascular smooth muscle cells, especially behind the fovea, the contraction of which may thin the choroid, thereby opposing the thickening caused by expansion of the lacunae. It has intrinsic choroidal neurons, also mostly behind the central retina, which may control these muscles and may modulate choroidal blood flow as well. These neurons receive sympathetic, parasympathetic and nitrergic innervation. The choroid has several functions: Its vasculature is the major supply for the outer retina; impairment of the flow of oxygen from choroid to retina may cause Age-Related Macular Degeneration. The choroidal blood flow, which is as great as in any other organ, may also cool and warm the retina. In addition to its vascular functions, the choroid contains secretory cells, probably involved in modulation of vascularization and in growth of the sclera. Finally, the dramatic changes in choroidal thickness move the retina forward and back, bringing the photoreceptors into the plane of focus, a function demonstrated by the thinning of the choroid that occurs when the focal plane is moved back by the wearing of negative lenses, and, conversely, by the thickening that occurs when positive lenses are worn. In addition to focusing the eye, more slowly than accommodation and more quickly than emmetropization, we argue that the choroidal thickness changes also are correlated with changes in the growth of the sclera, and hence of the eye. Because transient increases in choroidal thickness are followed by a prolonged decrease in synthesis of extracellular matrix molecules and a slowing of ocular elongation, and attempts to decouple the choroidal and scleral changes have largely failed, it seems that the thickening of the choroid may be mechanistically linked to the scleral synthesis of macromolecules, and thus may play an important role in the homeostatic control of eye growth, and, consequently, in the etiology of myopia and hyperopia.

Alteration in choroidal blood flow produced by local pressure

BACKGROUND

To investigate how transient pressure applied to the retinal pigment epithelium (RPE) layer and choroid affects choroidal blood flow in rabbits.

METHODS

Twelve rabbits underwent vitrectomy and local retinectomy. In nine of the rabbits a glass rod was used to exert brief pressure on the RPE layer and choroid. Three of the rabbits had no pressure indentation and were considered to be controls. The choroidal circulation was studied by indocyanine green (ICG) angiography. The retina and choroid were studied by postmortem histology.

RESULTS

Pressure on the RPE layer and choroid caused nonfluorescence in segments of retinal arteries and veins and reduced fluorescence in adjacent choroidal capillaries, producing a black region at the pressure site in the angiograms. The size of this region decreased during the angiogram, often accompanied by the appearance of fine channels considered to be flow through the partially blocked vessels; the obstructed ends of the vessels became increasingly hyperfluorescent. These changes lasted for about 24 h before the choroidal circulation recovered. Histology showed evidence of thrombotic-like material in choroidal arteries and veins at the areas of absent perfusion. After local retinectomies, there was no evidence of thrombosis in control eyes where no pressure had been applied.

CONCLUSION

Brief pressure on the RPE and choroid causes immediate reduction in flow through choroidal vessels, which appears to be due to local thrombosis in small segments of these vessels that resolves slowly. This may reflect a tendency for thrombi to form rapidly in choroidal vessels; it may also depend on neural reflexes causing vasoconstriction. The long time course of recovery could result in retinal ischemia and may underlie the pathophysiology of other pressure insults to the choroid.

Choroidal innervation in primate eyes

Arteries and arterioles of the choroid are surrounded by numerous nerve fibers staining for nitric oxide synthase (NOS) and vasoactive intestinal peptide (VIP). In most mammalian eyes these nerve fibers derive from the pterygopalatine ganglion via the facial nerve. Stimulation of the facial nerve causes vasodilation of the choroidal vasculature. In primates with a well developed fovea centralis there are ganglion cells in the choroidal stroma which in human eyes amount to around 2000. The postganglionic nerve fibers of these choroidal ganglion cells (CGC) join the perivascular nerve fiber plexus. The CGC stain for NOS and VIP like the nerve cells within the pterygopalatine ganglion. There are, however, differences between the two cell populations. Immunohistochemical and ultrastructural classification of the CGC show that in addition to NOS and VIP almost half of the cells stain for calretinin, single ones for neuropeptide Y (NPY) and galanin. A number of cells is in close contact with numerous boutons staining for nNOS, VIP, NPY, tyrosine hydroxylase (TH), vesicular monoaminergic transporter (VMAT)2, vesicular acetylcholine transporter (VACHT), calretinin, and NPY. These data indicate a more complex integrative function of CGCs e.g. volume regulation in parallel with ciliary muscle contraction during accommodation. Ultrastructural and immunohistochemical studies indicate, that CGCs in addition may have mechanosensory properties. Whether they are involved in volume-regulatory functions independent of accommodation is not yet known. In glaucoma disease the number of CGCs is significantly reduced. This holds true for eyes with primary open angle glaucoma, pseudoexfoliation glaucoma and experimentally induced monkey glaucoma indicating that elevated IOP is involved in the pathogenesis of glaucomatous CGC-degeneration.

Non-vascular smooth muscle cells in the human choroid: distribution, development and further characterization

To characterize further non-vascular smooth muscle cells (NVSMC) in the choroid of the human eye, extensive morphological studies were performed including a three-dimensional distribution of NVSMC in the adult human eye and their appearance during development. Whole mounts and sections through the choroid and sclera of eyes of 42 human donors (between the 13th week of gestation and 89 years of age) were stained with antibodies against smooth muscle actin and other markers for smooth muscle cells. On the basis of their morphological localization, three groups of NVSMC could be distinguished in the adult eyes: (a) a semicircular arrangement of NVSMC in the suprachoroid and inner sclera, around the entry of posterior ciliary arteries and nerves; (b) NVSMC parallel to the vessels in the posterior eye segment between the point of entry of the posterior ciliary arteries and the point of exit of the vortex veins; and (c) a dense plaque-like arrangement of NVSMC in the suprachoroid, overlying the foveal region. The last of these groups showed most pronounced interindividual differences. During development, the first NVSMC to be observed at the 20th week of gestation belonged to group b. A complete NVSMC network was first observed in a 6-year-old donor eye. All three groups stained positive for smoothelin, caldesmon and calponin in all localizations. The NVSMC show a distinct distribution that might reflect different aspects of their function in the choroid and suprachoroid. All cells could be histochemically characterized as truly contractile.

The origin of extrinsic nitrergic axons supplying the human eye

Nitrergic nerve fibres of intrinsic and extrinsic origin constitute an important component of the autonomic innervation in the human eye. The intrinsic source of nitrergic nerves are the ganglion cells in choroid and ciliary muscle. In order to obtain more information on the origin of extrinsic nitrergic nerves in the human eye, we obtained superior cervical, ciliary, pterygopalatine and trigeminal ganglia from six human donors, and stained them for neuronal nitric oxide synthase (nNOS) and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-D). In the superior cervical ganglia, nNOS/NADPH-D-positive varicose axons were observed whereas perikarya were consistently negative. Fewer than 1% of perikarya in the ciliary ganglia were labelled for nNOS/NADPH-D. The diameter of nNOS/NADPH-D-positive ciliary perikarya was between 8 and 10 microm, which was markedly smaller than the diameter of the vast majority of negative perikarya in the ciliary ganglion. More than 70% of perikarya in the pterygopalatine ganglia were intensely labelled for both nNOS and NADPH-D. In trigeminal ganglia, 18% of perikarya were nNOS/NADPH-D-positive. The average diameter of trigeminal nNOS/NADPH-D perikarya was between 25 and 45 microm. Pterygopalatine and trigeminal ganglia are the most likely sources for extrinsic nerve fibres to the human eye.

The effect of the nonspecific nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester on the choroidal compensatory response to myopic defocus in chickens

PURPOSE

Chick eyes show rapid compensation to retinal defocus. One component of this mechanism involves changes in the thickness of the choroid: when the retina is exposed to myopic defocus, the choroid thickens, pushing the retina forward; conversely, when the eye is exposed to hyperopic defocus, the choroid thins. The underlying mechanism(s) for these changes are unknown. We tested the hypothesis that nitric oxide might play a role.

METHODS

We examined the effect of the nonspecific nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) on the compensatory choroidal thickening in response to myopic defocus using two visual paradigms: first, in previously form-deprived "recovering" eyes and, second, in eyes wearing +15 D spectacle lenses. L-NAME was injected intravitreally after removal of the diffuser or immediately before putting on the lenses. In addition, we looked at the effect of L-NAME on experimentally thickened choroids (induced by 1 week of recovery from deprivation myopia or 1 week of +15 D lens wear) and on choroids of normal eyes. Eyes were measured using A-scan ultrasonography before the injections and at subsequent intervals for several days. As a control for the injection procedure, eyes with the same visual conditions were injected with saline. Fellow eyes were untreated and uninjected.

RESULTS

L-NAME inhibited choroidal thickening in both previously form-deprived eyes (2 vs. 117 microm; p < 0.001) and eyes wearing +15 D lenses (3 vs. 137 microm; p < 0.02). The effect was rapid, transient, and dose dependent (ED50, 0.26 micromoles). L-NAME produced thinning in experimentally thickened choroids (recovering: -116 microm; lenses: -219 microm) and in normal choroids (-47 microm) within 7 hours.

CONCLUSIONS

Nitric oxide may play a role in modulating choroidal thickness. The mechanism is as yet unknown.

The impact of ocular blood flow in glaucoma

Two principal theories for the pathogenesis of glaucomatous optic neuropathy (GON) have been described--a mechanical and a vascular theory. Both have been defended by various research groups over the past 150 years. According to the mechanical theory, increased intraocular pressure (IOP) causes stretching of the laminar beams and damage to retinal ganglion cell axons. The vascular theory of glaucoma considers GON as a consequence of insufficient blood supply due to either increased IOP or other risk factors reducing ocular blood flow (OBF). A number of conditions such as congenital glaucoma, angle-closure glaucoma or secondary glaucomas clearly show that increased IOP is sufficient to lead to GON. However, a number of observations such as the existence of normal-tension glaucoma cannot be satisfactorily explained by a pressure theory alone. Indeed, the vast majority of published studies dealing with blood flow report a reduced ocular perfusion in glaucoma patients compared with normal subjects. The fact that the reduction of OBF often precedes the damage and blood flow can also be reduced in other parts of the body of glaucoma patients, indicate that the hemodynamic alterations may at least partially be primary. The major cause of this reduction is not atherosclerosis, but rather a vascular dysregulation, leading to both low perfusion pressure and insufficient autoregulation. This in turn may lead to unstable ocular perfusion and thereby to ischemia and reperfusion damage. This review discusses the potential role of OBF in glaucoma and how a disturbance of OBF could increase the optic nerve's sensitivity to IOP.

Temporal relationship of choroidal blood flow and thickness changes during recovery from form deprivation myopia in chicks

When form deprived, young chicks rapidly develop axial myopia, from which they recover if the treatment is ceased at a sufficiently early age. The increased axial growth of the eye is accompanied by choroidal thinning and decreased choroidal blood flow (ChBF). In contrast, during the early part of the recovery process, the choroid thickens, shifting the retina towards the new plane of focus. Little information is available about ChBF during recovery from myopia. Because of the possibility that choroidal thickening during recovery from myopia might be driven by an increase in ChBF, the temporal relationship of ChBF and choroidal thickness changes was examined during such recovery. White Leghorn chicks were form deprived from 3 days of age for 2-3 weeks using detachable plastic diffusers. Axial ocular dimensions, including choroidal thickness, were then measured by high frequency A-scan ultrasonography at various times after the diffusers were removed up to 240 hr. ChBF was measured transclerally immediately following the A-scan ultrasonography, using laser Doppler flowmetry. In the chicks measured immediately after diffuser removal, the vitreous chamber was 29.9% longer, the choroid was 6.4% thinner and ChBF was 13.7% less in the treated than in the non-treated control eyes. These changes are characteristic of myopic chick eyes and are reversible in young eyes. Thus, in chicks examined 7 hr after diffuser removal, the ChBF in recovering eyes was now greater than that in control eyes. This ChBF increase peaked about 19 hr after the diffusers were removed. The mean increase in ChBF in treated eyes for the 7-30 hr monitoring period was 187%, relative to control eyes. ChBF in the treated eyes gradually returned to the control level after this time. By contrast to the early, transient increase in ChBF, significant choroidal thickening was not observed in treated eyes until 30 hr after diffuser removal, and continued to increase relative to control eyes over the remainder of the monitoring period, reaching a final mean value of 182%. This study demonstrates, in chick eyes recovering from form deprivation myopia, large increases in ChBF that preceded increases in choroidal thickness and were also more transient than the latter. These results raise the possibility that the increase in ChBF may trigger or even drive the subsequent onset of choroidal expansion, perhaps by facilitating the filling of the choroidal lymphatic lacunae that are well developed in the avian eye.

Intermediate-filament expression in ocular tissue

Intermediate-filament proteins (IFPs) occur in the intracellular cytoskeleton of eukaryotic cells, and their expression in diverse tissues is related both to embryology as well as to differentiation. Although the available information concerning their functional properties in vivo is still incomplete, antibodies against individual IFPs are commonly used in immunohistochemical procedures as markers for differentiation, and these antibodies are of outstanding value in the routine histopathological evaluation of tumor specimens. This review presents a compilation of the currently available data concerning IFP expression in normal and diseased ocular tissues. Representatives of every known class of IFP have been detected in normal ocular tissues. The external epithelia exhibit complex expression patterns of cytokeratin (CK) polypeptides, with CK3 and CK12 being specific markers of the corneal epithelium. Recent research has revealed that single mutant CK polypeptides may play a role in the pathogenesis of corneal dystrophies. The internal ocular epithelia reveal simple but specific patterns of IFP expression, these comprising simple-epithelial CKs and/or the mesenchymal IFP, vimentin. The IFP complement of the neuronal structures of the eye embraces several distinct IFP classes and reflects the diversity of the cell types present at these sites. With respect to ocular tumors, the IFP profile of melanomas might be correlated with metastatic potential. In conclusion, IFP analysis may be able to cast light on the pathogenesis of ocular diseases, as well as being a valuable adjunct in ophthalmopathological diagnosis.

An extensive system of extravascular smooth muscle cells exists in the choroid of the rabbit eye

We investigated the structural organization of the choroid especially with regard to the presence of extravascular smooth muscle (EVSM) cells in albino rabbits. The eyes were fixed by intracardiac perfusion and processed for light, confocal, and electron microscopy. An unlabeled monoclonal antibody against alpha-actin of smooth muscle and a horseradish-peroxidase-conjugated secondary antibody were used for immunodetection of smooth muscle actin by light microscopy. For confocal microscopy, whole mount choroids were immunostained with a fluorescein isothiocyanate-conjugated (FITC) antibody. Our investigations revealed that the choroidal vessels are enveloped by bundles of EVSM. In contrast to the circular orientation of the smooth muscle cells of the tunica media of the choroidal vessels, the cells of the EVSM system were oriented longitudinally along the external surface of the vessel wall. The EVSM cells were strongly immunopositive for smooth muscle alpha-actin and exhibited a green fluorescence of the FITC-labeled anti-alpha-actin antibody. Individual cells were elongated and spindle-shaped, had the usual ultrastructural features of smooth muscle cells and, in places, were organized as 20 layers. EVSM cells were present throughout the thickness of the choroid, but not between the fenestrated endothelial lining of the choriocapillaris and Bruch's membrane, and extended from the optic nerve to the ciliary body where they merged with the ciliary muscles. Based on the three dimensional organization, immunoreactivity, and cellular and subcellular features of the EVSM system as well as information in the literature, we hypothesize that, functionally, this system, in conjunction with the choroidal vasculature, contributes to the myogenic control of choroidal blood flow and tissue volume, and also affects the intraocular pressure as well as the refractive and accommodative state of the eye.

Influence of ophthalmic nerve fibers on choroidal blood flow and myopic eye growth in chicks

Ophthalmic sensory nerve fibers containing substance P and calcitonin gene-related peptide' innervate the choroid in mammals and are known to vasodilate choroidal blood vessels. The avian choroid is also innervated by ophthalmic nerve fibers containing substance P and calcitonin gene-related peptide. The present studies were carried out to determine the influence of these sensory fibers on choroidal blood flow in birds and characterize their interaction with manipulations affecting eye growth. In these studies, ChBF was measured using laser Doppler flowmetry in both eyes in the following groups of birds: (1) normal chicks; (2) chicks with right optic nerve transected for 2 weeks; (3) chicks with right optic nerve transected and a goggle over the right eye for 2 weeks; and (4) chicks with right optic and ophthalmic nerves transected and a goggle over the right eye for 2 weeks. The eyes were refracted and various ocular dimensions measured after the blood-flow measurements. It was found that optic nerve transection reduced ChBF to 30% of normal. Placing a goggle (which increases ocular temperature by 4 degrees C) over an optic nerve transected eye nearly doubled choroidal blood flow over that in an optic nerve transected eye without a goggle. Additional transection of the ophthalmic nerve in a goggled optic nerve-transected eye, yielded choroidal blood flow that was indistinguishable from that in a nongoggled optic nerve-transected eye. Optic nerve transection had a slight stunting effect on axial growth of the eye. While myopic axial elongation was observed in goggled eyes with the optic nerve cut, the extent of myopia was less than in normal goggled eyes. Ophthalmic nerve transection further reduced the myopia induced by goggling in an optic nerve cut eye. These results suggest that ophthalmic nerve input to the choroid exerts a vasodilatory influence, which is activated in a goggled eye. This increased choroidal blood flow may be in response to elevated ocular temperatures caused by the goggling and this increase appears to be masked in goggled eyes with an intact optic nerve by the reduction in choroidal blood flow normally accompanying myopic eye growth. Our results thus show that the induction of myopic eye growth (as in our optic nerve cut eyes with a goggle) need not be accompanied by a decrease in choroidal blood flow from the baseline no-goggle condition (in this case, with the optic nerve cut).

Structure, development and function of cytoskeletal elements in non-neuronal cells of the human eye

The cytoskeleton, of which the main components in the human eye are actin microfilaments, intermediate filaments and microtubules with their associated proteins, is essential for the normal growth, maturation, differentiation, integrity and function of its cells. These components interact with intra- and extracellular environment and each other, and their profile frequently changes during development, according to physiologic demands, and in various diseases. The ocular cytoskeleton is unique in many ways. A special pair of cytokeratins, CK 3 and 12, has apparently evolved only for the purposes of the corneal epithelium. However, other cytokeratins such as CK 4, 5, 14, and 19 are also important for the normal ocular surface epithelia, and other types may be acquired in keratinizing diseases. The intraocular tissues, which have a relatively simple cytoskeleton consisting mainly of vimentin and simple epithelial CK 8 and 18, differ in many details from extraocular ones. The iris and lens epithelium characteristically lack cytokeratins in adults, and the intraocular muscles all have a cytoskeletal profile of their own. The dilator of the iris contains vimentin, desmin and cytokeratins, being an example of triple intermediate filament expression, but the ciliary muscle lacks cytokeratin and the sphincter of the iris is devoid even of vimentin. Conversion from extraocular-type cytoskeletal profile occurs during fetal life. It seems that posttranslational modification of cytokeratins in the eye may also differ from that of extraocular tissues. So far, it has not been possible to reconcile the cytoskeletal profile of intraocular tissues with their specific functional demands, but many theories have been put forward. Systematic search for cytoskeletal elements has also revealed novel cell populations in the human eye. These include transitional cells of the cornea that may represent stem cells on migration, myofibroblasts of the scleral spur and juxtacanalicular tissue that may modulate aqueous outflow, and subepithelial matrix cells of the ciliary body and myofibroblasts of the choroid that may both participate in accommodation. In contrast to the structure and development of the ocular cytoskeleton, changes that take place in ocular disease have not been analysed systematically. Nevertheless, potentially meaningful changes have already been observed in corneal dystrophies (Meesmann's dystrophy, posterior polymorphous dystrophy and iridocorneal endothelial syndrome), degenerations (pterygium) and inflammatory diseases (Pseudomonas keratitis), in opacification of the lens (anterior subcapsular and secondary cataract), in diseases characterized by proliferation of the retinal pigment epithelium (macular degeneration and proliferative vitreoretinopathy), and in intraocular tumours (uveal melanoma). In particular, upregulation of alpha-smooth muscle actin seems to be a relatively general response typical of spreading and migrating corneal stromal and lens epithelial cells, trabecular cells and retinal pigment epithelial cells.