Peripapillary fundus perimetry in eyes with glaucoma

AIMS

To evaluate, with fundus perimetry, the peripapillary differential light threshold (DLT) in eyes with glaucoma and ocular hypertension (OHT), and compare it with peripapillary retinal nerve fibre layer (RNFL) thickness.

METHODS

35 glaucomatous, 29 OHT and 24 control eyes were included. Peripapillary DLT at 1 degrees from the optic nerve head was quantified with fundus perimetry; peripapillary RNFL thickness was measured over the same area by optical coherence tomography.

RESULTS

Mean (SD) peripapillary DLT was 19.2 (1.7), 17.6 (4.2) and 10.1 (6.9) dB in control, OHT and glaucomatous eyes, respectively (p<0.001). Mean (SD) RNFL thickness was 98.4 (35.3), 83.9 (35.1) and 55.8 (28.2) microm, respectively (p<0.001). Mean peripapillary DLT showed higher sensitivity and specificity in differentiating the three groups compared with RNFL thickness.

CONCLUSION

Progressive, significant reduction of peripapillary DLT was documented in OHT and glaucomatous eyes compared with controls (p<0.001). DLT reduction parallels RNFL reduction.

Fluorescein filling defects of the optic nerve head in normal tension glaucoma, primary open-angle glaucoma, ocular hypertension and healthy controls

BACKGROUND

To evaluate fluorescein filling defects of the optic nerve head in normal tension glaucoma (NTG), primary open-angle glaucoma (POAG), ocular hypertension (OHT) and controls.

METHODS

Forty patients with NTG (mean age 55 +/- 10 years), 40 patients with POAG (mean age 55 +/- 11 years), 40 patients with OHT (mean age 53 +/- 13 years), and 40 age-matched controls (mean age 54 +/- 11 years) were included in a prospective study. Video fluorescein angiograms were performed by means of a scanning laser ophthalmoscope. The extent of absolute filling defects of the optic nerve head was assessed (as a percentage of the disc area) using digital image analysis. Visual fields were tested by automatic static perimetry (Humphrey Field Analyzer, programme 24-2).

RESULTS

Absolute filling defects were significantly larger in patients with NTG (12.2 +/- 15.5%) and POAG (12.9 +/- 13.1%) compared to patients with OHT (1.2 +/- 3.6%) and healthy controls (0.1 +/- 0.5%) (p < 0.0001). The area under the receiver operating characteristic (ROC) curve was 0.806 for NTG vs healthy controls, and 0.812 for POAG vs OHT. Absolute filling defects are significantly correlated to the global indices mean deviation (r = -0.63, p < 0.0001), pattern standard deviation (r = 0.61, p < 0.0001), and corrected pattern standard deviation (r = 0.62, p < 0.0001) and significantly correlated to horizontal (r = 0.50, p < 0.0001) and vertical (r = 0.53, p < 0.0001) cup-to-disc-ratios.

CONCLUSIONS

Fluorescein filling defects of the optic disc representing capillary dropout are present in NTG and POAG. The extent of these filling defects is correlated to visual field loss and morphological damage. Fluorescein angiography may be useful in the diagnosis and management of NTG and POAG.

Longitudinal non-invasive proton NMR spectroscopy measurement of vitreous lactate in a rabbit model of ocular hypertension

To determine whether vitreous lactate concentrations are correlated with intraocular pressure (IOP) rise, retinal ganglion cell (RGC) damage, and nerve fiber layer (NFL) thickness decrease in a rabbit model of ocular hypertension. Also, to learn whether proton nuclear magnetic resonance ((1)H-NMR) spectroscopy can provide sequential, non-invasive in vivo measurements of vitreous lactate. Intra-anterior chamber injections of 20-mum latex beads were used to impede aqueous drainage in New Zealand White rabbits, causing an elevation of IOP. Group I consisted of 12 rabbits in which unilateral elevations in IOP were achieved. Group II consisted of 6 rabbits in which treatment did not cause a change in IOP. The contralateral eye served as a control in both groups. Control eyes received an equal volume injection of vehicle only. IOP was measured for two pre-treatment days and then on post-treatment days 1, 3, 5, 7, 9, 16, 23, 30, and 37. (1)H-NMR spectroscopy was used to measure changes in vitreous lactate concentrations that may be associated with the onset and progression of the pathophysiology. Post-mortem histochemical analysis at the light microscope level was used to quantify changes in the retinal NFL thickness and in the numbers of RGC, and correlate them with IOP and percent change in lactate levels. Baseline IOP in Group I control and treated eyes were 12.0+/-1.9 and 12.5+/-1.3 mmHg, respectively. Between days 5 and 9 post-treatment, the IOP in Group I treated eyes (n=12) rose to 23.9+/-4.2 mmHg. IOP in the control eyes remained unchanged (12.0+/-1.6). Vitreous lactate levels in Group I treated eyes increased by 100%, from pre-treatment values. Levels in control eyes remained unchanged. In Group I, IOP and percent change in lactate concentration in treated eyes were closely correlated throughout the study period (r=0.95; p< or =0.05). Group II control and treated eyes showed no significant changes in either IOP or lactate. Group I treated eyes had a reduced NFL thickness (65+/- 4 microm; n=5) at the temporal medullary ray (MR) compared with control eyes (45+/-6 microm). A smaller reduction was found in the nasal MR areas, where thickness was 53+/-3 microm in treated eyes and 66+/-4 microm in control eyes. RGC numbers also were decreased in the treated eyes (241,222+/-10,920 cells) vs. 322,311+/-8726 cells in control eyes. TdT-mediated dUTP nick-end labeling (TUNEL) indicated that RGC loss in the treated eyes was most likely due to apoptosis. In vivo changes in lactate can be monitored non-invasively over time using (1)H-NMR spectroscopy. Vitreous lactate concentrations increased and returned to baseline concurrently with IOP. The brief elevation in IOP produced a reduction in both the RGC cell numbers and in the thickness of the NFL.

[The measurement of central corneal thickness of normal subjects and glaucomatous patients with optical coherence tomography]

OBJECTIVE

To evaluate central corneal thickness (CCT) of normal subjects, patients with primary open angle glaucoma (POAG), normal tension glaucoma (NTG) and ocular hypertension (OHT) using optical coherence tomography (OCT).

METHODS

One hundred and forty-three eyes of 143 normal subjects, 36 eyes of 36 patients with POAG, 39 eyes of 39 patients with NTG and 40 eyes of 40 patients with OHT were enrolled. CCT were measured by OCT3 and analyzed using ANOVA. The relationship of CCT and intraocular pressure (IOP) measured by Goldmann applanation tonometry were analyzed by linear regression. The inter-observer and intra-observer agreement of CCT measurement by OCT were analyzed by interclass correlation coefficient (ICC).

RESULTS

The average CCT of normal subjects, patients with POAG, NTG and OHT were (525.31 +/- 32.18) microm, (531.87 +/- 31.58) microm, (507.61 +/- 21.56) microm and (574.09 +/- 27.84) microm, respectively. There was no significant difference between normal subjects and patients with POAG (P = 0.099). The average CCT of OHT patients was larger than those of other groups (P < 0.001). The average CCT of patients with NTG was less than those of other groups (P < 0.001). There was positive relationship between CCT and IOP in normal subjects (r = 0.318, R2 = 0.101, P < 0.001). The ICC of inter-observer and intra-observer agreement of CCT measurement by OCT were 0.995 and 0.996 respectively.

CONCLUSIONS

Central corneal thickness could be measured by OCT accurately. The average CCT in the patients with NTG was thinner, but the average CCT in the patients with OHT was thicker than that of normal subjects. CCT could affect IOP measurement in the application of Goldmann applanation tonometry but with little significant.

Longitudinal changes in central corneal thickness and their relation to glaucoma status: an 8 year follow up study

AIMS

To determine if central corneal thickness (CCT) changes over time and if this change relates to glaucoma progression.

METHODS

39 patients (64 eyes) with open angle glaucoma, ocular hypertension, glaucoma suspect status, or a normal eye examination were examined at two visits. CCT, age, race, sex, family history of glaucoma, presence of diabetes and systemic hypertension, diagnosis, visual acuity, spherical equivalent, intraocular pressure, vertical and horizontal cup to disc ratios, number of glaucoma medications prescribed, Advanced Glaucoma Intervention Study (AGIS) score and mean deviation of Humphrey visual fields, and interventions required were recorded. Statistical analysis used the Wilcoxon signed ranks test, linear regression, and analysis of variance.

RESULTS

Between the two visits (mean 8.2 years apart), mean CCT decreased by 17 mum in right eyes (p<0.002) and by 23 mum in left eyes (p<0.001). This decrease was greater in right eyes of patients with primary open angle glaucoma than in normals (p = 0.041). There was no significant association between change in CCT and other examination parameters. Change in CCT was not associated with topical carbonic anhydrase inhibitor use.

CONCLUSION

In this longitudinal study, CCT decreased over time, but this may not be related to glaucoma progression.

Three portable tonometers, the TGDc-01, the ICARE and the Tonopen XL, compared with each other and with Goldmann applanation tonometry*

Three portable tonometers, the TGDc-01, the ICARE and the Tonopen XL, were compared with each other and to Goldmann applanation tonometry in a large group of healthy subjects and patients with ocular hypertension or glaucoma (n = 103). Measurements performed with the ICARE and the Tonopen XL were in good agreement with that of the Goldmann tonometer. Intraocular pressure (IOP) values measured with the TGDc-01 were significantly lower and showed more variability. The 95% limits of agreement (portable tonometer - Goldmann) were -17 to +10 mmHg for the TGDc-01, -6 to +7 mmHg for the ICARE and -6 to +8 mmHg for the Tonopen. Corneal thickness could not explain the differences between an IOP measured with the portable tonometers and an IOP measured with the Goldmann tonometer. Patient comfort was slightly higher for ICARE when compared with the Tonopen.

The relative effects of corneal thickness and age on Goldmann applanation tonometry and dynamic contour tonometry

AIMS

To establish the effects of central corneal thickness (CCT) on intraocular pressure (IOP) measured with a prototype Pascal dynamic contour tonometer (DCT), to evaluate the effect of CCT and age on the agreement between IOP measured with the Pascal DCT and Goldmann applanation tonometer (GAT), and to compare the interobserver and intraobserver variation of the DCT with the GAT.

METHODS

GAT and DCT IOP measurements were made on 130 eyes of 130 patients and agreement was assessed by means of Bland-Altman plots. The effect of CCT and age on GAT/DCT IOP differences was assessed by linear regression analysis. Interobserver and intraobserver variations for GAT and DCT were assessed in 100 eyes of 100 patients.

RESULTS

The mean difference (95% limits of agreement) between GAT and DCT was -0.7 (-6.3 to 4.9) mm Hg. GAT/DCT IOP differences increased with thicker CCT (slope 0.017 mm Hg/microm, 95% CI 0.004 to 0.03, r2 = 0.05, p = 0.01), and with greater age, slope 0.05 mm Hg/year (95% CI 0.012 to 0.084, r2 = 0.05, p = 0.01). The intraobserver variability of GAT and DCT was 1.7 mm Hg and 3.2 mm Hg, respectively. The interobserver variability was (mean difference (95% limits of agreement)) 0.4 (-3.5 to 4.2) mm Hg for GAT and 0.2 (-4.9 to 5.3) mm Hg for DCT.

CONCLUSIONS

GAT is significantly more affected than DCT by both CCT and subject age. The effect of age suggests an age related corneal biomechanical change that may induce measurement error additional to that of CCT. The prototype DCT has greater measurement variability than the GAT.

Malignant hypertension: ocular manifestations

Malignant hypertension may be the first manifestation of systemic hypertension. We report a clinical case of a Caucasian 41-year-old man with no previous history of blood hypertension seen at casualty because of blurred vision. Fundus examination disclosed optic disk swelling, retinal hemorrhages and infarcts. The blood pressure was 220/130 mmHg. After the appropriate management of hypertension, optic disk and retinal edema resolved, leaving minor changes as mild optic disk pallor and hard exudates.

Effects of a non-selective beta-blocker on adult rat anterograde axonal transport and retinal ganglion layer after increased intraocular pressure

The aim of this study was to examine the effects of timolol in an experimental model of elevated intraocular pressure (IOP). Three episcleral veins of rats with normal IOP were cauterized. Three months later we examined the effects on anterograde axonal transport from the retinal ganglion cells (RGCs) to the superior colliculus (SC) as well as on the number of neurons in the retinal ganglion layer (RGL). These parameters were also studied in a group of rats submitted to treatment with timolol after confirming that their IOP was still raised after two weeks. After the surgical procedure, the mean IOP of the experimental eyes increased to 33.5+/-1.06 mmHg (1.25 fold compared to the control group) and three months later the IOP remained significantly elevated; however, after a long period of treatment with timolol the IOP was 14.05+/-0.81 mmHg, similar to that of the control group. In the group with normal IOP, labelling with horseradish rabbit peroxidase (HRP) at 120 minutes and 24 hours postinjection showed continuous staining from the retina to the SC. In the experimental group the optic nerve head (ONH) was completely negative, although in the group treated with timolol there was partial block of axonal transport in the ONH, in which the staining was slightly more intense. The number of neurons in the RGL, counted by immunohistochemical labelling with Neu-N, showed that in eyes with normal and elevated IOP there were 423+/-11 neurons/mm(2) and 283+/-10 neurons/mm(2), respectively. After treatment with timolol the number of neurons (331+/-10 cells/mm(2) increased compared with elevated IOP eyes, although the number did not reach that of the control group. These results indicate that treatment with timolol, started two weeks after the surgical procedure, was partially neuroprotective because the loss of neurons in the RGL was lower than in untreated animals, though not sufficient to re-establish normal axonal transport.

Morphometric evaluation of changes with time in optic disc structure and thickness of retinal nerve fibre layer in chronic ocular hypertensive monkeys

We examined the time course of changes in optic disc structure by means of a scanning laser ophthalmoscope (Heidelberg Retina Tomograph, HRT) in ocular hypertensive (experimental glaucoma) monkeys, and clarified the relationships between the histological RNFL thickness and HRT parameters. Further, the time course of changes in retinal nerve fiber layer (RNFL) thickness in individual eyes was measured using a scanning laser polarimeter with fixed corneal polarization compensator (GDx FCC). In the present study, two separate experiments were carried out. A chronic intraocular pressure (IOP) elevation was induced by laser trabeculoplasty in the left eye in 11 cynomolgus monkeys. In Experiment 1, the HRT and GDx parameters were measured 12 weeks after the laser treatment in 10 eyes in five monkeys. In Experiment 2, the time course of changes in the HRT and GDx parameters was examined before and 1, 3, 4, 5, 6, 8, 10, 12, 14, and 16 weeks after the laser treatment in 12 eyes in six monkeys. The retardation values (thickness parameters) obtained from the GDx were used to derive thickness and ratio parameters in the superior, inferior, nasal and temporal quadrants. Ratio parameters were expressed as a ratio of superior and inferior quadrant to nasal quadrant. After the last measurements, each eye was enucleated, and retinal cross sections were prepared for histological analysis. In the left (hypertensive) eyes, IOP was persistently elevated throughout the observation periods in both Experiments 1 and 2. In the HRT measurements in Experiment 1, seven out of eight global topographic parameters (exception, disc area) were statistically different between the hypertensive and control eyes 12 weeks after the laser treatment. In Experiment 2, the HRT parameters changed in a time-dependent manner, but each of them almost plateaued at about 4 weeks after the laser treatment. Significant correlations were seen between the histological mean RNFL thickness at 1.5 disc diameters from the optic disc margin and the HRT parameters in 21 eyes from 11 monkeys in Experiments 1 and 2. Especially good correlations with histological mean RNFL thickness were seen for the rim volume and cup volume. In Experiment 1, good correlations were found between GDx ratio parameters and histological RNFL thickness in individual right control eyes (n=5). In individual left experimental glaucoma eyes of Experiment 2 (n=6), GDx ratio parameters declined in a time-dependent manner alongside the IOP elevation. In conclusion, alongside the IOP elevation, time-related changes in optic disc topography and RNFL thickness were demonstrated in monkey eyes using HRT and GDx. HRT (rim and cup) parameters showed good correlations with histological RNFL thickness, and significant interrelations.

A 6-month assessment of bimatoprost 0.03% vs timolol maleate 0.5%: hypotensive efficacy, macular thickness and flare in ocular-hypertensive and glaucoma patients

AIM

To compare 6 months of treatment with bimatoprost and timolol in terms of their hypotensive efficacy and secondary effects, including changes in macular thickness and the inflammatory reaction induced in the anterior chamber.

METHODS

A prospective, randomized, parallel-group trial performed on 30 eyes of 30 patients per group. The main outcome measure was the difference between the IOP value taken between the baseline visit and the 6-month-visit. Macular thickness determined through optical coherence tomography and anterior chamber inflammation estimated using the laser flare meter was also evaluated. Adverse events were recorded during the study period.

RESULTS

Bimatoprost treatment gave rise to a significantly lower mean IOP than timolol in all follow-up visits as from the first month (P<0.05). Bimatoprost achieved high percentage IOP reductions from baseline in a significantly higher proportion of patients (P<0.05). Macular thickness and anterior chamber flare failed to vary significantly both between the two groups and within each group during the 6-month evaluation (P>0.05).

CONCLUSIONS

Bimatoprost 0.03% once daily showed a greater efficacy then timolol 0.05% twice daily in patients with elevated IOP. No significant differences were detected in macular thickness or anterior uveitis using optical coherence tomography and laser flare photometry.

The influence of central corneal thickness and age on intraocular pressure measured by pneumotonometry, non-contact tonometry, the Tono-Pen XL, and Goldmann applanation tonometry

AIMS

To evaluate the influence of central corneal thickness (CCT) on intraocular pressure (IOP) measurements made with the Goldmann applanation tonometer (GAT), Tono-Pen XL, ocular blood flow tonograph (OBF), and Canon TX-10 non-contact tonometer (NCT).

METHODS

CCT was recorded for either eye (randomly selected) of each of 105 untreated patients with ocular hypertension and glaucoma attending the glaucoma research unit at Moorfields Eye Hospital. For each of the selected eyes, IOP was measured with the GAT (two observers), Tono-Pen, OBF, and NCT in a randomised order. The relation of measured IOP and of inter-tonometer differences with CCT and subject age was explored by linear regression analysis.

RESULTS

A significant association between measured IOP and CCT was found with each instrument. The change in measured IOP for a 10 mum increase in CCT was 0.28, 0.31, 0.38, and 0.46 for the GAT, Tono-Pen, OBF, and NCT, respectively (all p< or = 0.05). There was a significant association between the NCT/GAT differences and CCT, with a tendency of NCT to overestimate GAT in eyes with thicker corneas. There was a significant association between GAT/Tono-Pen and OBF/Tono-Pen differences and age, with a tendency of GAT and OBF to overestimate the Tono-Pen in eyes of older subjects.

CONCLUSION

IOP measurement by all four methods is affected by CCT. The NCT is affected by CCT significantly more than the GAT. Subject age has a differential effect on the IOP measurements made by the GAT and OBF compared to the Tono-Pen.

Morphometric assessment of normal, suspect and glaucomatous optic discs with Stratus OCT and HRT II

AIMS

To compare morphometric parameters and diagnostic performance of the new Stratus Optical Coherence Tomograph (OCT) Disc mode and the Heidelberg Retina Tomograph (HRT); to evaluate OCT's accuracy in determining optic nerve head (ONH) borders.

METHODS

Controls and patients with ocular hypertension, glaucoma-like discs, and glaucoma were imaged with OCT Disc mode, HRT II, and colour disc photography (DISC-PHOT). In a separate session, automatically depicted ONH shape and size in OCT were compared with DISC-PHOT, and disc borders adjusted manually where required. In a masked fashion, all print-outs and photographs were studied and discs classified as normal, borderline, and abnormal. The Cohen kappa method was then applied to test for agreement of classification. Bland-Altman analysis was used for comparison of disc measures.

RESULTS

In all, 49 eyes were evaluated. Automated disc margin recognition failed in 53%. Misplaced margin points were more frequently found in myopic eyes, but only 31/187 were located in an area of peripapillary atrophy. Agreement of OCT with photography-based diagnosis was excellent in normally looking ONHs, but moderate in discs with large cups, where HRT performed better. OCT values were consistently larger than HRT values for disc and cup area. Compared with HRT, small rim areas and volumes tended to be minimized by OCT, and larger ones to be magnified.

CONCLUSIONS

Stratus OCT Disc protocol performed overall well in differentiating between normal and glaucomatous ONHs. However, failure of disc border recognition was frequently observed, making manual correction necessary. ONH measures cannot be directly compared between HRT and OCT.

Neurochemical evidence to implicate elevated glutamate in the mechanisms of high intraocular pressure (IOP)-induced retinal ganglion cell death in rat

High intraocular pressure (IOP)-induced ischemia is a model for retinal neurodegeneration that recapitulates pathological features almost identical to those seen in patients after central retinal or ophthalmic artery occlusion and may also represent a model of acute angle closure glaucoma. Using this experimental model, we present data indicating that acute IOP elevation for 45 min is followed by a progressive decline in the number of retinal ganglion cells (RGC) which appear to die via an apoptotic mechanism. The observation that systemic treatment with MK801, a N-methyl-d-aspartate (NMDA) receptor antagonist, with GYKI52466, a non-NMDA receptor antagonist, or with l-NAME, an inhibitor of nitric oxide synthase (NOS), prevents the RGC loss observed 24 after IOP elevation strongly suggests an excitotoxic, glutamate-mediated, mechanism of RGC death. The latter deduction is strengthened by the evidence that a microdialysis probe placed into the retinal tissue of rats bearing IOP elevation revealed an increase (90% as compared to baseline value) in glutamate levels that peaked 130 min after the beginning of reperfusion and was reversed by a pre-treatment with MK801. Collectively, our data suggest that acute elevation of IOP increases intraretinal levels of glutamate with consequent abnormal activation of NMDA and non-NMDA subtypes of glutamate receptors and increased NOS activity leading to excitotoxic, glutamate-mediated, RGC death.

Microvessels of the human optic nerve head: ultrastructural and radioreceptorial changes in eyes with increased IOP

BACKGROUND

Ultrastructural, morphological modifications in the microvessels of the optic nerve head were studied in human eyes with normal intraocular pressure (IOP), with slightly increased IOP, and with strongly increased IOP. Moreover, the distribution of beta-adrenergic receptors was analyzed in the same samples.

METHODS

Six enucleated human eyes were studied. Small pieces of the optic nerve head and of iridocorneal angle (including trabecular meshwork) were dissected immediately after autopsy. The sections were studied with transmission electron microscopy and autoradiography. Radiolabelled pindolol was used to locate beta-adrenergic receptors topographically on fresh sections of human eye.

RESULTS

Transmission electron microscopy demonstrated that elevated IOP induces ultrastructural modifications of the microvessels of the optic nerve head. Autoradiographic experiments showed the presence and distribution of beta-adrenergic receptors in the optic nerve head of eyes with both normal and increased IOP.

INTERPRETATION

Increased IOP initially compresses the microvessels of the optic nerve head. The number of beta-adrenergic receptors increased markedly in the eyes with raised IOP. Further studies are needed to clarify the physiological and pathological roles of these receptors.

Primate glaucoma models

The monkey model of ocular hypertension (OHT) with its resultant optic neuropathy closely reflects the optic neurodegeneration associated with human glaucoma. Utilization of the experimental glaucoma model (ExpG) in non-human primates (NHP) has led to advances in the understanding of aqueous humor dynamics, glaucomatous changes in the visual pathways from photoreceptors to the visual cortex, and anterior and posterior ocular segment pharmacological effects.

Central corneal thickness in primary open angle glaucoma, pseudoexfoliative glaucoma, ocular hypertension, and normal population

PURPOSE

This study was designed to determine the relationship between central corneal thickness (CCT) and intraocular pressure (IOP) measured by applanation tonometer in glaucomatous, ocular hypertensive, and normal eyes.

METHODS

A total of 125 subjects were included in the study. Twenty-six had primary open angle glaucoma (POAG), 25 had pseudoexfoliative glaucoma (PXG), 24 had ocular hypertension (OHT), and 50 of them were normal. IOP values were measured by Goldmann applanation tonometer whereas CCT values were measured by ultrasonic pachymeter.

RESULTS

CCT values in the OHT group (595.75+/-22.52 microm) were greater than the CCT values of the POAG group (539.92+/-21.50 microm), the PXG group (526.28+/-31.73 microm), and the normal group (533.96+/-29.25 microm) (p<0.05). Eight patients who were diagnosed with OHT showed IOP values of 21 mm Hg or lower with corrected IOP values according to CCT.

CONCLUSIONS

Increased CCT may lead to falsely high values of IOP measured with Goldmann applanation tonometer. In this study, when IOP values of the OHT group were redefined according to the formulae regarding the CCT, the authors noted that one third of them were normal. Determination of the CCT in OHT cases is crucial since it has great impact on IOP values, measured with applanation tonometer, which is the main parameter in the diagnosis and follow-up of glaucoma.

Varying effects of corneal thickness on intraocular pressure measurements with different tonometers

AIMS

To compare the intraocular pressure (IOP) measurements using the Goldmann applanation tonometer (GAT), noncontact tonometer (NCT), and ocular blood flow tonometer (OBFT), and to evaluate the effects of varying central corneal thickness (CCT) on the readings.

METHODS

Ultrasound pachymetry and tonometry were performed on 170 eyes. Using the corrected GAT values that took CCT into account as the standard, we calculated the NCT and OBFT measurement errors related to the CCT variable by a linear regression model. Group comparisons were performed with the chi2 test and one-way ANOVA test. The correlation between the various tonometer measurements was analysed by Pearson's correlation method.

RESULTS

Both the NCT (r=0.872, P<0.001) and OBFT measurements (r=0.861, P<0.001) were highly correlated with the GAT measurements. IOP measurements using the three tonometers were all correlated with CCT (all P<0.001), with the NCT measurements showing the greatest regression coefficient (beta=0.063, r=0.650) and the GAT measurements the least (beta=0.037, r=0.496). A linear regression model indicated that a 10 microm change in CCT resulted in a NCT measurement deviation of 0.47-0.98 mmHg and an OBFT measurement deviation of 0.29-0.81 mmHg.

CONCLUSION

Pressure readings with the GAT, NCT, and OBFT are all affected by CCT, with the NCT being the one most affected and the GAT the least. Our findings suggest CCT an essential variable to consider in interpreting IOP readings, especially for the NCT measurements.

Ocular structure and function in an aged monkey with spontaneous diabetes mellitus

Diabetes mellitus develops spontaneously in middle-aged, obese rhesus monkeys, thus making them a good model for examining the effects of co-morbid factors on the development of end-organ damage. Changes in structure and function in the eyes of one monkey who spontaneously developed type 2 diabetes are reported here. This animal had concomitant hypertension, high levels of triglycerides and serum cholesterol, and a low fraction of high-density lipoprotein. The eyes showed intraretinal hemorrhages and large areas of retinal capillary nonperfusion. Indo-cyanin green (ICG) angiography revealed a large area of non- or poorly perfused choriocapillaris in one eye, and immunohistochemistry showed loss of viable choriocapillaries in this region. Both basal laminar deposits and hard drusen were present on areas of Bruch's membrane adjacent to nonviable choriocapillaris. Blood flow via the nasal posterior ciliary arteries to this section of choroid was not detectable by color duplex Doppler ultrasound, indicating contribution of extraocular vascular disease to ischemia in this eye. There was a severe decline in number of photoreceptor inner and outer segments, and corresponding reductions in the multifocal electroretinogram (ERG), in the areas of choriocapillaris loss. The ganzfeld ERG indicated loss in both inner and outer retinal function. Much of the ganglion cell layer was absent throughout the retina, possibly reflecting the effect of diabetes as well as chronic open angle glaucoma; the latter diagnosis supported by elevated intraocular pressures and excavated optic disks. In summary, high resolution, enzyme histochemical and histopathological analyses of a diabetic hypertensive monkey retina and choroid after serial functional in vivo analyses have demonstrated the relationship between vascular dysfunction and visual function loss. Choroidal vascular dysfunction in both large and small vessels was associated with age-related macular degeneration-like changes in Bruch's membrane and photoreceptor degeneration.

[Analysis of optic nerve head by confocal scanning laser ophthalmoscope in ocular hypertension]

PURPOSE

To analyze optic nerve head topography using confocal the scanning laser ophthalmoscope (CSLO) in ocular hypertension in comparison to normal eyes.

PATIENTS AND METHODS

We examined 25 patients with ocular hypertension and 27 normal controls. All of them had a complete ophthalmic examination. Optic nerve head analysis was performed by using a CSLO-type Heidelberg retina tomograph (HRT). The following stereometric parameters were evaluated: disc area, area and volume of cup, cup/disc ratio, area and volume of neuroretinal rim, mean and maximal cup depth, cup shape measure, height variation contour, mean retinal nerve fiber layer thickness, and retinal nerve fiber layer (RNFL) cross-section area.

RESULTS

In ocular hypertension eyes, rim volume, height variation contour and RNFL thickness showed a statistically significant reduction compared to normal eyes.

CONCLUSION

HRT appears to be an important tool in detecting early damage of retinal nerve fiber layer in ocular hypertension.

Glutamate-Induced Glutamine Synthetase Expression in Retinal Müller Cells after Short-term Ocular Hypertension in the Rat

PURPOSE

To determine the effect of intraocular pressure (IOP) elevation on glutamate-induced expression of glutamine synthetase (GS) in retinal Müller cells of rat eyes.

METHODS

Six groups of three rats each were studied. Group I was a normal control group. In Group II, one eye received an intravitreal glutamate injection (75 nmoles) while the contralateral eye served as control. In Groups III and IV, IOP was raised in one eye by episcleral vein cauterization. Moderately elevated IOP was maintained for 1 day in Group III or 1 week in Group IV (35 +/- 1.9-45 +/- 5.2 mm Hg). An additional two groups of rats received bilateral intravitreal glutamate injections (75 nmoles) immediately (Group V), or 6 days (Group VI), after induction of IOP elevation in one eye. One day after glutamate injection the rats in all groups were killed, and the eyes enucleated and fixed. Retinas from left and right eyes of each animal were embedded together in LR White resin (Ted Pella, Redding, CA). Sections were processed for GS immunolabeling with antibodies to GS by two-stage immunogold labeling with silver enhancement. Images of labeled retinas from the two eyes were captured under identical light microscopic conditions and the GS immunoreactivity in Müller cells was compared between the left and right retinas in the same section by image analysis. An additional five rats were included in Group II and the retinas were analyzed by Western blot analysis to confirm immunohistochemical findings.

RESULTS

Similar to the finding in the control group (Group I), the GS immunoreactivity of the left and right eyes of Group III and IV remained unchanged even though the right eyes in the two groups had elevation of IOP lasting for 24 hours and 1 week, respectively. However, GS levels were significantly increased by 40 +/- 5.7% in normotensive eyes 24 hours after intravitreal injection of glutamate (Group II). The rise in GS immunoreactivity was abolished in eyes with acute IOP elevation (Group V). In contrast, when the eyes were exposed to high IOP for 1 week (Group VI), the glutamate-induced increase in GS immunoreactivity was restored.

CONCLUSIONS

Elevated levels of vitreal glutamate can increase the expression of GS in retinal Müller cells. This increase was blocked if IOP was acutely elevated for 24 hours but was restored if IOP remained elevated for 1 week. This finding suggests that moderate elevation of IOP causes only short-term functional changes of glutamate metabolism (amidation) by retinal Müller cells. However, it is not known to what extent endogenous extracellular glutamate can regulate GS expression in normal eyes or in eyes with glaucoma.

Efficacy and Safety of Memantine Treatment for Reduction of Changes Associated with Experimental Glaucoma in Monkey, II: Structural Measures

PURPOSE

To determine, using anatomic measurements, whether daily oral dosing with memantine is both safe and effective to reduce the injury associated with experimental glaucoma in primates.

METHODS

Argon laser treatment of the anterior chamber angle was used to induce chronic ocular hypertension (COHT) in the right eyes of 18 macaque monkeys. Nine animals were daily orally dosed with 4 mg/kg memantine while the other nine animals received vehicle only. Measurements of intraocular pressure (IOP) from both eyes of all animals were made at regular intervals. Appearance of the optic nerve head, retinal vessels, and surrounding retina was documented with stereo fundus photographs obtained at multiple time points throughout the study. Measurements of optic nerve head topography were obtained from confocal laser scans made from animals with the highest IOPs at approximately 3, 5, and 10 months after elevation of IOP. At approximately 16 months after IOP elevation, animals were killed and histologic counts of cells in the retinal ganglion cell (RGC) layer were made.

RESULTS

Histologic measurements showed that, for animals with moderate elevation of IOP, memantine treatment was associated with an enhanced survival of RGCs in the inferior retina. Measurements of optic nerve head topography showed less IOP-induced change in memantine-treated animals. This effect was seen in measurements of both the cup and the neuroretinal rim. A comparison of these same histologic and morphologic measurements in normotensive eyes from the two treatment groups showed that memantine treatment was not associated with any significant effects on these eyes.

CONCLUSIONS

Histologic measurements of RGC survival as well as tomographic measurements of nerve head topography show that systemic treatment with memantine, a compound which does not lower intraocular pressure, is both safe and effective to reduce changes associated with experimental glaucoma.

Alterations in neurofilament light in optic nerve in rat kainate and monkey ocular hypertension models

The purpose of this study is to evaluate the changes in neurofilament light (NF-L) protein in the optic nerve in rat kainate and monkey ocular hypertension models. In the rat model, optic nerve damage was induced by kainate injection into the vitreous body. In the monkey model, photocoagulation of the trabecular meshwork led to laser-induced ocular hypertension. NF-L in optic nerve extract was quantified by quantitative immunoblot using an imaging analyzer. The amount of NF-L in optic nerve was compared between normal and kainate-treated groups at 7 days after kainate injection. Specimens from rat optic nerves and retinas were evaluated histologically to examine the correlations between damage and amount of NF-L in the optic nerve. In monkeys, the amount of NF-L in the optic nerve was compared between control fellow and ocular hypertensive eyes. Injection of kainate induced morphological optic nerve and retinal damage in rats. The amount of NF-L in the optic nerve was significantly reduced in kainate-treated eyes (vs. normal eyes). The amount of NF-L correlated with the cell count in the ganglion cell layer and the axon number in the optic nerve at 7 days after kainate injection. Further, 6-cyano-7-nitro-quinoxaline-2,3-dione, a non N-methyl-D-aspartate receptor antagonist, suppressed the kainate-induced reduction in NF-L and retinal damage. In the monkey model, ocular hypertension and morphological optic nerve damage were shown by laser-treated eyes. The amount of NF-L in the optic nerve was reduced in laser-treated eyes. In conclusion, in rat kainate and monkey ocular hypertension models, immunoblot evaluation of NF-L shows the reduction of the amount of NF-L in the optic nerves of treated-eyes. The amount of NF-L correlated with the morphological retinal and optic nerve damage in rats. These findings indicate that immunoblot evaluation of NF-L in the optic nerve may provide a quantitative index of optic nerve damage.

Effect of corneal parameters on measurements using the pulsatile ocular blood flow tonograph and Goldmann applanation tonometer

AIMS

To investigate the effect of central corneal thickness and corneal curvature on intraocular pressure measurements using the pulsatile ocular blood flow tonograph and the Goldmann applanation tonometer, and to assess the agreement between the pulsatile ocular blood flow tonograph and the Goldmann applanation tonometer in intraocular pressure measurement.

METHODS

479 subjects underwent intraocular pressure measurements with the Goldmann applanation tonometer and the pulsatile ocular blood flow tonograph. Of these, 334 patients underwent additional measurement of central corneal thickness with an ultrasonic pachymeter and corneal curvature measurement with a keratometer.

RESULTS

The intraocular pressure measurements obtained with both the Goldmann applanation tonometer and the pulsatile ocular blood flow tonograph varied with central corneal thickness and mean keratometric reading. Intraocular pressure measured using the Goldmann applanation tonometer increased by 0.027 mm Hg per micro m increase in central corneal thickness. Intraocular pressure measured using the pulsatile ocular blood flow tonograph increased by 0.048 mm Hg per micro m increase in central corneal thickness. For an increase of 1 mm of mean corneal curvature there was rise in intraocular pressure of 1.14 mm Hg measured by the Goldmann applanation tonometer and of 2.6 mm Hg measured by the pulsatile ocular blood flow tonograph. When compared to the Goldmann applanation tonometer, the pulsatile ocular blood flow tonograph underestimated at low intraocular pressure and overestimated at higher intraocular pressure.

CONCLUSION

Central corneal thickness and corneal curvature affected measurements obtained with the pulsatile ocular blood flow tonograph more than they affected measurements obtained with the Goldmann applanation tonometer.

Symmetry Analysis for Detecting Early Glaucomatous Changes in Ocular Hypertension Using Optical Coherence Tomography

PURPOSE

To compare symmetry analysis of the retinal nerve fiber layer (RNFL) in ocular-hypertensive, normal, and glaucomatous eyes using optical coherence tomography (OCT).

METHODS

Thirty-three consecutive ocular-hypertensive patients (33 eyes), 25 normal volunteers (25 eyes), and 35 open-angle glaucoma patients (35 eyes) were enrolled in this study. Circular OCT scans were obtained using a diameter of 3.4 mm around the optic disc. RNFL thickness was measured, and a symmetry analysis was performed using symmetry ratios. To calculate the symmetry ratios, the circle was divided into the superior and inferior hemiretina. The superior hemiretina was further subdivided into three (area I, temporal 45 degrees; area II, superior 90 degrees; and area III, nasal 45 degrees ) or five (with areas 1-5, each spanning 36 degrees ) zones. The symmetry ratios were defined as the ratios comparing the RNFL thickness within each of the zones with that in the analogous zone in the inferior hemiretina.

RESULTS

RNFL thickness measurements could distinguish glaucomatous eyes from other groups, but could not distinguish ocular-hypertensive from normal eyes. However, the symmetry analysis revealed differences between ocular-hypertensive and normal eyes in area II (mean +/- SD, 0.77 +/- 0.16 vs. 0.85 +/- 0.12, P = 0.0379).

CONCLUSIONS

Early glaucomatous RNFL changes might exist in some areas of ocular-hypertensive eyes, and a symmetry analysis may be a useful method for detecting these changes.