Use of the GDx to detect differences in retinal nerve fibre layer thickness between normal, ocular hypertensive and early glaucomatous eyes

PURPOSE

The GDx is a scanning laser polarimeter that has been developed to allow the quantitative analysis of retinal nerve fibre layer (RNFL) thickness. The purpose of this study was to determine whether differences in the RNFL thickness between normal, ocular hypertensive and glaucomatous eyes could be detected using the GDx.

METHODS

RNFL analysis was carried out using the GDx on 33 normal, 145 ocular hypertensive (OHT) and 44 glaucomatous (POAG) eyes. The inclusion criteria for entry into the study did not include the clinical appearance of the RNFL or optic disc, thus eliminating an important source of selection bias. The Kruskal-Wallis one-way analysis of variance was used to determine whether any significant differences existed among the groups in mean total and quadrantic RNFL thickness. When significant differences were found, specific inter-group analysis was carried out using the Mann-Whitney U-test.

RESULTS

Significant differences in RNFL thickness were found for the mean total, superior and inferior quadrant values between normals and OHT eyes as compared with POAG eyes. No significant differences were found for these values between the normal and OHT eyes.

CONCLUSION

Analysis of RNFL thickness using the GDx was able to detect differences between POAG eyes compared with normal and OHT eyes, although there was considerable overlap between groups. Further assessment of the technique is required to determine whether it may be useful in screening for the presence of early glaucomatous damage.

[The retinal nerve fiber layer in glaucoma. II. The status of the nerve fiber layer and development of changes in the visual field. Prospective study]

PURPOSE

To determine whether retinal nerve fiber layer (RNFL) photographs can predict future glaucoma visual field damage.

METHODS

In a prospective study 158 red free photographs of the RNFL were made from November 1994 to June 1995. 28 eyes of 19 patients with ocular hypertension (repeated intraocular pressure over 21 mmHg and normal visual fields--Peristat 433 Rodenstock--at first examination) could be re-examined for an average time of 42.3 (SD 4.5) months.

RESULTS

Only in one eye with normal RNFL at the first examination typical glaucoma visual field defects appeared (6%), but in 6 of 12 eyes (50%) with photographically demonstrable RNFL defects. The difference was statistically significant.

CONCLUSION

There is only a minor probability, that visual field defects would appear during 3-5 years in eyes with normal RNFL photographs (6%), but about 50% of eyes with originally found RNFL defects.

Patterns of intraocular pressure elevation after aqueous humor outflow obstruction in rats

PURPOSE

To determine the diural intraocular pressure (IOP) response of Brown Norway rat eyes after sclerosis of the aqueous humor outflow pathways and its relationship to optic nerve damage.

METHODS

Hypertonic saline was injected into a single episcleral vein in 17 animals and awake IOP measured in both the light and dark phases of the circadian cycle for 34 days. Mean IOP for light and dark phases during the experimental period were compared with the respective pressures of the uninjected fellow eyes. Optic nerve cross sections from each nerve were graded for injury by five independent masked observers.

RESULTS

For fellow eyes, mean light- and dark-phase IOP was 21 +/- 1 and 31 +/- 1 mm Hg, respectively. For four experimental eyes, mean IOPs for both phases were not altered. Six eyes demonstrated significant mean IOP elevations only during the dark phase. Of these, five showed persistent, large circadian oscillations, and four had partial optic nerve lesions. The remaining seven eyes experienced significant IOP elevations during both phases, and all had extensive optic nerve damage.

CONCLUSIONS

Episcleral vein injection of hypertonic saline is more likely to increase IOP during the dark phase than the light. This is consistent with aqueous outflow obstruction superimposed on a circadian rhythm of aqueous humor production. Because these periodic IOP elevations produced optic nerve lesions, both light- and dark-phase IOP determinations are necessary for accurate correlation of IOP history to optic nerve damage in animals housed in a light- dark environment.

Long-term topical timolol and blood lipids: the Blue Mountains Eye Study

OBJECTIVES

To examine whether an association exists between long-term use of topical timolol and blood lipids, including high-density lipoprotein cholesterol (HDL-C), cholesterol, and triglycerides, among participants of the Blue Mountains Eye Study.

METHODS

From 1992 through 1994, a detailed medical and eye examination was performed in 3,654 people aged 49 years or older, representing 82% of permanent residents in two postcode areas west of Sydney. Glaucoma and ocular hypertension were diagnosed, and an ophthalmic history was taken, including use of topical timolol. Fasting blood tests were performed in 89% of subjects. Lipid levels were compared in subjects using topical timolol for at least 1 year with those not using timolol, after excluding people using oral beta-blockers, topical beta1-selective agents, or oral lipid-lowering medications.

RESULTS

Analyses compared blood lipids of 63 people who had used topical timolol for at least 1 year with 2,597 nonusers. No statistically significant differences were found in any blood lipid mean levels between treated and untreated people, after multivariate adjustment. However, subgroup analyses of men and women separately showed that male timolol users had a mean value of HDL-C 0.13 mmol/L (11%) lower then the mean value of male nonusers, while female timolol users had a mean value of HDL-C 0.09 mmol/L (5%) higher than the mean for female nonusers. There were no statistically significant associations between timolol treatment duration and HDL-C or other lipid levels. Previously reported adverse effects of oral beta-blockers on blood lipid levels were confirmed.

CONCLUSIONS

These population-based data suggest that long-term administration of topical timolol for glaucoma or ocular hypertension can cause adverse effects on HDL-C in men, but not in women. The magnitude of the effect in men was similar to that previously described in a number of short-term studies.

Crete, Greece glaucoma study

PURPOSE

To investigate the prevalence of primary open-angle glaucoma (POAG) in a randomized sample of the inhabitants of the island of Crete.

PATIENTS AND METHODS

In 18 different villages in all four prefectures of the island of Crete, patients were randomly selected from 1993 through 1998, and an in situ study was accomplished. The sampling fraction (covered by the 1991 census) in each village was approximately 5%. Patients were considered to have POAG when the morphologic aspect of a glaucomatous optic disc was present, and/or a nerve fiber layer defect and a visual field defect was present. The presence of Pseudoexfoliation syndrome (PEX) and pseudoexfoliative glaucoma (PEXG) was also investigated.

RESULTS

The prevalence of glaucoma in Crete was 2.80%. Of those diagnosed with POAG, 9.67% had an intraocular pressure (IOP) under 21 mm Hg, and 25.80% had PEX. The prevalence of simple ocular hypertension without glaucoma was found in 6.58% of the patients. The ratio of subjects with hypertensive glaucoma to those with simple ocular hypertension was 1:2.6.

CONCLUSION

The prevalence of POAG and exfoliation glaucoma appears to be quite high in Crete. Further research will be needed to set more accurate criteria for earlier diagnosis and to enable more efficient organization of the health care system.

Latanoprost versus timolol gel to prevent ocular hypertension after phacoemulsification and intraocular lens implantation

PURPOSE

To evaluate the efficacy of latanoprost and timolol gel in preventing ocular hypertension in the early period after phacoemulsification and posterior chamber intraocular lens (PC IOL) implantation.

SETTING

Department of Ophthalmology and Visual Sciences, Prince of Wales Hospital, Hong Kong, China.

METHODS

This prospective randomized double-masked clinical trial comprised patients with uncomplicated cataract having phacoemulsification with PC IOL implantation. They were randomly assigned to 1 of 3 groups: postoperative application of timolol 0.5% gel-forming solution (Timoptol-XE(R)) (Group 1), latanoprost 0.005% (Group 2), and control (Group 3). Intraocular pressure (IOP) was measured 2, 4, and 24 hours postoperatively. The anterior chamber was examined for the levels of cells and flare using slitlamp biomicroscopy.

RESULTS

Group 1 had a significantly greater reduction in mean IOP 2, 4, and 24 hours after phacoemulsification and PC IOL implantation than Group 3 (P <.05). There were no significant differences between Groups 2 and 3 at any interval (P. 05). No excessive postoperative anterior chamber inflammation was observed in any group.

CONCLUSIONS

A single dose of latanoprost given after phacoemulsification and PC IOL implantation did not produce a significant IOP-lowering effect when compared with a control group in the first 24 hours postoperatively. A single dose of timolol gel produced a significant postoperative IOP decrease as soon as 2 hours and up to 24 hours after surgery. Timolol gel and latanoprost are safe, but timolol is more effective than latanoprost in preventing postoperative ocular hypertension.

Chronology of optic nerve head and retinal responses to elevated intraocular pressure

PURPOSE

To determine the chronology of optic nerve head and retinal responses to elevated intraocular pressure (IOP).

METHODS

After 1 to 39 days of unilaterally elevated IOP, experimental and fellow rat eyes were examined for morphology and immunohistochemical labeling alterations and for ganglion cell DNA fragmentation.

RESULTS

Mean IOP for the experimental eyes was 36 +/- 8 mm Hg, an approximately 15-mm Hg elevation above normal values. By 7 days of pressure elevation above 40 mm Hg, endogenous immunostaining for brain-derived neurotrophic factor and neurotrophin 4/5 was absent from the nerve head and superior retina, whereas normal labeling was present in the inferior retina and distal optic nerve of these same eyes. These changes were preceded by a loss of gap junctional connexin43 labeling and astrocytic proliferation in the nerve head and by increased retinal ganglion cell layer apoptosis in the retina. Nerve head depletion of neurotrophins coincided with evidence of axonal degeneration, loss of astrocytic glial fibrillary acidic protein staining, and spread of collagen VI vascular immunolabeling. After longer durations at these same pressures, neurotrophin labeling returned to nerve head glia and scattered retinal ganglion cells.

CONCLUSIONS

Optic nerve head and retinal responses, including the depletion of endogenous neurotrophins, are readily identified in the rat eye after experimental IOP elevation. However, the apparent chronology of these responses suggests that the withdrawal of neurotrophic support was not the only determinant of retinal ganglion cell apoptosis and axonal degeneration in response to pressure.

The application of water drinking test on the evaluation of trabeculectomy patency

The water drinking test (WDT) was once frequently used as a diagnostic tool for glaucoma, but not so often nowadays. In this study, we investigated the potential use of the WDT on the evaluation of trabeculectomy patency. Twenty age-matched volunteers and thirty-six glaucoma patients who were to receive trabeculectomy procedure were enrolled in this study. The WDT was given to the volunteers once and to all glaucoma patients before undergoing trabeculectomy and at certain intervals after the procedure. The WDT was performed in a standard manner. We defined four parameters after performing the WDT: Initial Pressure [IP, intraocular pressure (IOP) level before the WDT]; Slope of Ascending Trend (SOAT, the slope between baseline IOP and the highest IOP level); Peak Pressure (PP, the highest IOP level during the WDT); and End Pressure (EP, the IOP level after the WDT). It was found that the results of the WDT and trabeculectomy patency were strongly correlated. The four parameters in success and failure cases were significantly different at the last follow up: IP: (15.2 +/- 3.6 vs. 25.3 +/- 6.4, p<0.01); SOAT: (0.9 +/- 0.3 vs. 1.8 +/- 1.2, p<0.01); PP: (19.2 +/- 6.4 vs. 39.5 +/- 12.2, p<0.01); EP: (15.5 +/- 4.8 vs. 29.4 +/- 8.2, p<0.01). Thus, it was observed in this study that WDT was not only easy and safe to perform, but also valuable in evaluating the patency of trabeculectomy.

Short-term effect of latanoprost and timolol eye drops on tear fluid and the ocular surface in patients with primary open-angle glaucoma and ocular hypertension

PURPOSE

To investigate and compare the short term effects of topical latanoprost and timolol on the tear fluid and ocular surface condition in patients with bilateral primary open angle glaucoma or ocular hypertension.

METHODS

Thirty-seven patients were included in this randomized, double-masked, parallel group study. Patients received either latanoprost 0.005% (n= 18) or timolol 0.5% (n= 19) instilled once daily in the morning for a treatment period of 27 days. Routine ophthalmic examinations, including intraocular pressure measurement, as well as tests to evaluate tear fluid and the ocular surface were performed.

RESULTS

After one drop of medication, tear secretion was significantly reduced by timolol, but not by latanoprost. At the end of the study the break-up time (BUT) was significantly decreased in the timolol group but not in the latanoprost group. The BUT still remained in the normal range in both groups, although it is important to note that timolol was administered at half the clinical dose. Both latanoprost and timolol tended to increase Rose-Bengal staining of the cornea and conjunctiva after one month of treatment but no statistically significant difference was found between the groups. Corneal sensitivity was within the normal range for all patients during the study.

CONCLUSION

Regarding ocular surface effects, no clinically important differences between latanoprost and timolol were observed as all the effects remained in the normal range.

Aqueous humor dynamics in monkeys with laser-induced glaucoma

This study determines the effects of laser-induced glaucoma on aqueous humor dynamics of 18 cynomolgus monkeys. Baseline measurements of 12 monkeys included intraocular pressure (IOP) by pneumatonometry, aqueous flow by fluorophotometry and outflow facility by tonography. Beginning 4 to 14 days later, the trabecular meshwork of one eye was treated repeatedly with laser photocoagulation until elevated IOP was induced. Thirty-six to 75 days after the last laser treatment, all measurements were repeated. Between 1.7 and 11.4 years after laser treatment, the same 12 monkeys plus 6 additional monkeys underwent IOP and aqueous flow measurements. In addition, outflow facility was determined with fluorophotometry, and uveoscleral outflow was both calculated (n=18) and measured with an intracameral tracer (n=7). In glaucoma eyes compared to control eyes (n=12), IOP was increased (p<0.04) by at least 8 mmHg at Time 1 (1 to 3 months) or Time 2 (3 to 4 years) after laser treatment; aqueous flow was reduced (p=0.0007) by 46% at Time 1 but returned to baseline levels at Time 2; tonographic outflow facility was reduced (p=0.0008) by 71% at Time 1. In lasered eyes compared to control eyes, fluorophotometric outflow facility was reduced (p=0.0008; n=18) by 63%, and uveoscleral outflow was increased (p<0.05), whether calculated or measured with tracers at least 1 year after laser treatment. The increased IOP in monkeys with laser-induced glaucoma was caused by a sustained reduction in outflow facility. The uveoscleral outflow increase was not enough to prevent the rise in IOP.

Digital imaging and microtexture analysis of the nerve fiber layer

PURPOSE

To describe the design of a digital retinal nerve fiber layer (RNFL) imaging techniques and present a new approach to measure the differences in RNFL patterns.

METHODS

A digital camera body is connected to a wide-angle camera to obtain images of the RNFL, which are displayed in workstations throughout the clinic. In the on-line archive, images in Joint Photographics Experts Group (JPEG) format (100 KB per frame) are used. The hypothesis that changes in RNFL structure can be seen as changes in the microtexture of digital images was tested using an information theoretical approach (Kullback Information Distance, KID). A large KID value indicates a large difference, and a small KID value indicates a small difference in microtexture between the two regions. The material of this pilot study consists of 9 patients with glaucoma, 8 patients with ocular hypertension, and 7 normal subjects.

RESULTS

The median KID value in the glaucoma group was 3.5, compared with the median KID values of 0.6 in the control groups. Although a trend could be seen in the measured values, because of a small sample size, the differences were not statistically significant. Five of 24 (21%) KID values overlapped between the glaucomatous group and the other two groups.

CONCLUSION

Although digital imaging produces good quality RNFL images, further research is needed to establish minimum accepted specifications for digital imaging. In this pilot study, only the microtexture of the RNFL was measured in digital images. In the future, the approach can be expanded to include also properties of macrotexture and full color palette.

The retinal nerve fiber layer thickness in ocular hypertensive, normal, and glaucomatous eyes with optical coherence tomography

OBJECTIVE

To quantitatively assess and compare the thickness of the retinal nerve fiber layer (RNFL) in ocular hypertensive eyes with normal and glaucomatous eyes using the Optical Coherence Tomograph (OCT 2000, software version A4X1; Humphrey Instruments, San Leandro, Calif).

METHODS

The mean RNFL thickness of ocular hypertensive (n = 28) eyes was compared with age-matched normal (n = 30) and glaucomatous (n = 29) eyes. Subject eyes were classified into diagnostic groups based on intraocular pressure, stereoscopic disc photographs, and standard automated perimetry. Three circular scans were obtained for each eye at a diameter of 3.4 mm around the optic disc. In each eye, average RNFL thickness measurements were obtained in temporal, superior, nasal, and inferior quadrants. A single index of average RNFL thickness throughout 360 degrees also was obtained.

RESULTS

Mean (95% confidence interval) RNFL was significantly thinner in ocular hypertensive eyes than in normal eyes, 72.8 microm (66.4-78.1 microm) and 85.8 microm (80.2-91.7 microm), respectively. More specifically, RNFL was significantly thinner in ocular hypertensive eyes than in normal eyes in the inferior quadrant, 84.8 microm (75.6-94.0 microm) vs 107.6 microm (99.3-115.9 microm); and in the nasal quadrant, 44.1 microm (37.5-51.7 microm) vs 61.8 microm (53.0-65.6 microm). Retinal nerve fiber layer was significantly thinner in glaucomatous eyes than in ocular hypertensive and normal eyes throughout 360 degrees and in all quadrants.

CONCLUSION

These findings suggest that quantitative differences in RNFL thickness exist between age-matched ocular hypertensive, normal, and glaucomatous eyes.

Increased intraocular pressure and visual field defects in high resistance wind instrument players

OBJECTIVE

In this twofold study, part 1 aimed to determine whether the playing of high resistance wind instruments elevates intraocular pressure (IOP) and if so, to investigate the mechanism of IOP elevation and whether its magnitude differs while playing high resistance versus low resistance instruments. The purpose of part 2 was to evaluate whether high resistance players have a greater incidence of glaucomatous changes than other musicians.

DESIGN

Three case reports and a cross-sectional study.

PARTICIPANTS

Two players of high resistance instruments and one player of high and low resistance wind instruments participated in part 1 of the study. Nine high resistance wind players, 12 low resistance wind players, and 24 nonwind players were recruited among professional musicians in the Boston area to participate in part 2.

INTERVENTION

In part 1, IOP and uveal thickness changes were measured by pneumatonometry and ultrasound biomicroscopy in two participants playing their high resistance wind instruments (trumpet and oboe) and in a third participant playing both high (trumpet) and low (clarinet and saxaphone) resistance instruments. Each musician in part 2 underwent medical and musical history, measurement of IOP, Humphrey visual field testing, slit-lamp examination, gonioscopy, and dilated examination.

MAIN OUTCOME MEASURES

Intraocular pressure and uveal thickness changes, and visual field loss and optic nerve head appearance were the main parameters measured in part 1 and part 2, respectively.

RESULTS

In part 1, pneumatonometry showed IOP elevation dependent on the force of blowing, and ultrasound biomicroscopy revealed uveal thickening associated with IOP elevation. The magnitude of IOP elevation was dependent on the amount of expiratory resistance provided by the particular instrument. Part 2 showed that life hours of high resistance wind instrument playing had a significant relationship to abnormal visual field (P = 0.03) and corrected pattern standard deviation (CPSD) scores (P = 0.007) in univariate logistic regression and univariate linear regression, respectively. A 0.011-unit increase in CPSD for each 1000 life hours of high resistance wind playing was found.

CONCLUSIONS

High and low resistance wind musicians experience a transient rise in their IOP while playing their instruments as a result least in part of uveal engorgement. The magnitude of IOP increase is greater in high resistance wind players versus low resistance wind players. High resistance wind musicians had a small but significantly greater incidence of visual field loss (abnormal fields and increased CPSD scores) than other musicians, which was related to life hours of playing. The cumulative effects of long-term intermittent IOP elevation during high resistance wind instrument playing may result in glaucomatous damage, which could be misdiagnosed as normal-tension glaucoma.

Optic disc size in ocular hypertension

PURPOSE

To study the optic disc size in eyes with ocular hypertension (OHT) in comparison to primary open-angle glaucoma (POAG) and normals.

METHODS

Optic disc photographs obtained with the Nidek 3dx NM camera were digitized (Nikon coolscan) and disc area calculated using Littmann correction in a randomly chosen eye of 28 OHT, 42 POAG and 30 normal subjects. OHT was defined as increased intraocular pressure with no disc or field changes suggestive of glaucoma with open angles.

RESULTS

The optic disc area in OHT was 9.47 +/- 1.09 mm2; 12.27 +/- 2.87 mm2 in POAG; and 12.11 +/- 2.83 mm2 in normal individuals.

CONCLUSION

Using magnification corrected morphometry and the criteria for OHT diagnosis, the optic disc area in OHT was significantly smaller (p < 0.0001) in POAG and normals.

Confirmation of the rat model of chronic, moderately elevated intraocular pressure

We have confirmed the usefulness of the rat model of chronic, moderately elevated intraocular pressure (IOP) for studying loss of retinal ganglion cells, and as a model for pharmacological neuroprotection studies that may be relevant to treating human glaucoma. By unilaterally cauterizing three episcleral vessels, as described previously in the literature by another laboratory, we observed an approximately 1.6-fold increase in IOP compared to the contralateral eye (18.6 vs 11.5 mm Hg, respectively). Elevated IOP persisted for 6 months without re-treatment. Cupping of the optic disk was observable by examination, in vivo. In 6 months, there was an approximately 40% loss of retinal ganglion cells in the peripheral retina. This model provides a reproducible and quantitative model for pharmacological experiments using neuroprotective agents.

Isoforms of nitric oxide synthase in the optic nerves of rat eyes with chronic moderately elevated intraocular pressure

PURPOSE

To investigate the hypothesis that nitric oxide (NO) in the optic nerve heads of rats with chronic moderately elevated intraocular pressure (IOP) contributes to neurotoxicity of the retinal ganglion cells, the presence of the three isoforms of nitric oxide synthase (NOS) was determined in the tissue.

METHODS

Unilateral chronic moderately elevated IOP was produced in rats by cautery of three episcleral vessels. Histologic sections of optic nerves from eyes with normal IOP and with chronic moderately elevated IOP were studied by immunohistochemistry and by immunoblot analysis. Polyclonal antibodies to NOS-1, NOS-2, NOS-3, and glial fibrillary acidic protein (GFAP) were localized with immunoperoxidase.

RESULTS

In the optic nerve of rat eyes with normal IOP, NOS-1 was constitutively present in astrocytes, pericytes and nerve terminals in the walls of the central artery. NOS-2 was not present in eyes with normal IOP. In these eyes, NOS-3 was constitutively present in the vascular endothelia of large and small vessels. Rat eyes treated with three-vessel cautery had sustained elevated IOP (1.6 fold) for at least 3 months. In these eyes, no obvious changes in NOS-1 or NOS-3 were noted. However, at time points as early as 4 days of chronic moderately elevated IOP, NOS-2 appeared in astrocytes in the optic nerve heads of these eyes and persisted for up to 3 months. Immunoblot analysis did not detect differences in NOS isoforms.

CONCLUSION

The cellular distributions of constitutive NOS isoforms in the rat optic nerve suggest physiological roles for NO in this tissue. NOS-1 in astrocytes may produce NO as a mediator between neighboring cells. NO, produced by NOS-1 in pericytes and nitrergic nerve terminals and by NOS-3 in vascular endothelia, is probably a physiological vasodilator in this tissue. In eyes with chronic moderately elevated IOP, NOS-2 is apparently induced in astrocytes. The excessive NO production that is associated with this isoform may contribute to the neurotoxicity of the retinal ganglion cells in eyes with chronic moderately elevated IOP.

Optic disk size in open-angle glaucoma: the Blue Mountains Eye Study

PURPOSE

To compare optic disk size in eyes of subjects classified as normal with the eyes of subjects with open-angle glaucoma, ocular hypertension, or pseudoexfoliation syndrome in an older population-based sample.

METHODS

The Blue Mountains Eye Study examined 3,654 subjects. Vertical disk diameter was measured from stereoscopic disk photographs, and we used spherical equivalent refraction to correct for magnification. Analyses used all eyes in a general estimating equation model.

RESULTS

Mean disk diameter was 1.556 mm in glaucomatous eyes, significantly different (P <.05) than normal eyes (1.506 mm) and eyes with ocular hypertension (1.494 mm) or pseudoexfoliation (1.501 mm).

CONCLUSIONS

Patients with glaucoma have slightly larger optic disks than nonglaucomatous subjects.

Central corneal thickness in low-tension glaucoma

BACKGROUND

It is possible that the intraocular pressure (IOP) is underestimated in eyes whose central cornea is thinner than normal. The objective of this study was to determine and establish the significance of central corneal thickness in patients with low-tension (normal-tension) glaucoma compared with those with chronic open-angle glaucoma (COAG) or ocular hypertension and healthy eyes.

METHODS

The study was carried out from February 1998 to May 1999. Central corneal thickness was measured by ultrasonic pachymetry and IOP was measured by Goldmann applanation tonometry in 25 patients with low-tension glaucoma (untreated IOP less than 21 mm Hg with evidence of optic nerve head damage and corresponding visual field loss on automated perimetry), 80 patients with COAG (untreated IOP 21 mm Hg or greater with evidence of optic nerve head damage and corresponding visual field loss on automated perimetry), 16 patients with ocular hypertension (untreated IOP 21 mm Hg or greater, with normal optic nerve head and no history of glaucoma or elevated IOP, and normal visual field on automated perimetry) and 50 control subjects (untreated IOP less than 21 mm Hg with normal optic nerve head and no history of glaucoma or elevated IOP). Analysis with Pearson's product-moment correlation was performed to determine the correlation of IOP and central corneal thickness, and one-way analysis of variance was used to compare corneal thickness between groups.

RESULTS

The central cornea was significantly thinner in the low-tension glaucoma group (mean 513.2 mu [standard deviation (SD) 26.1 mu]) than in the COAG group (mean 548.2 mu [SD 35.0 mu]) and the control group (mean 556.7 mu [SD 35.9 mu]) (p < 0.001). No significant difference in corneal thickness was found between the COAG and control groups. The ocular hypertension group had significantly thicker corneas (mean 597.5 mu [SD 23.6 mu]) than the three other groups (p < 0.001).

INTERPRETATION

Patients with low-tension glaucoma may have thinner corneas than patients with COAG and healthy subjects. This results in underestimation of their IOP. Corneal thickness should be taken into account when managing these patients to avoid undertreatment.

Quantitative morphologic and functional evaluation of the optic nerve head in chronic open-angle glaucoma

Glaucoma leads to morphologic changes of the optic nerve head and to functional defects. Morphologic changes in the three-dimensional surface structure of the optic nerve head at its entrance site into the globe can be examined by laser scanning tomography. The standard technique for evaluating functional defects in glaucoma is static computerized perimetry. We compared these two techniques to determine which is more sensitive for follow-up of glaucomatous damage of the optic nerve head. If decreased function is presumed to precede imminent cell death, visual field analysis should be the more sensitive method, as cell death results in absolute defects of the visual field. However, the neuronal networks do not necessarily function in this way. In the case of loss of individual elements in the neuronal network, the complex linkages, even at the retinal level, are able to maintain functions and compensate for loss of function, which means that visual field defects would not be prominent. If the damage increases with time and is accompanied by a progressive loss of ganglion cells, however, compensation is eventually no longer possible, and the functional defects then become measurable by visual field analysis. Thus, morphologic absolute changes may be more prominent than visual field defects in the early stages of glaucoma. To evaluate the quantitative relationship between morphometrically measurable defects of the optic nerve head and measurable functional defects, we first examined the visual field with static computerized perimetry and then evaluated the surface structure with a laser scanning tomograph in 90 patients with chronic open-angle glaucoma, 10 patients with ocular hypertension, and 10 patients without any eye disease. Based on the 95th percentile of the standardized rim/disk area ratio, we calculated the relative rim area loss and correlated this with the mean defect in visual field analysis. The scatterplot shows an exponential curve. In the early stages of glaucoma, visual field defects were less prominent than morphologic absolute changes; 40% of the neuroretinal rim area is lost by glaucomatous optic nerve damage before first defects in visual field analysis appear. In late stages of glaucoma, changes in perimetry are more prominent than those observed with biomorphometry. These results show that in the follow-up of patients with early stages of glaucomatous damage, special attention should be given to morphologic absolute changes. In patients with advanced glaucoma, progress of the damage should be observed by repeated functional, rather than morphologic, examinations. It is important to keep in mind, however, that the sensitivity of any method is dependent on technology. One reason why functional tests may not be as sensitive as morphologic examination in observing patients with early stages of glaucoma may simply be that functional tests are not yet sensitive enough to detect early damage.

Effects of elevated intraocular pressure on haemoglobin oxygenation in the rabbit optic nerve head: a microendoscopical study

Intraocular pressure dependent reactions of optic nerve head vasculature and intracapillary haemoglobin oxygenation (HbO(2); oxygen saturation) were studied in the center and at the rim of the rabbit optic nerve head (ONH) as well as in the choroid, by a new combination of microendoscopy and simultaneous haemoglobin spectrophotometry. In 13 anesthetized albino rabbits the vasculature and the intracapillary Hb-oxygenation were studied by a microendoscope which was introduced into the eye bulb. Photometric measurements were performed via a beam splitter with the Erlangen micro-lightguide spectrophotometer (EMPHO) from the center of the endoscopic picture. The haemoglobin oxygenation was calculated by real time analysis of the spectral curves. Intraocular pressure was elevated stepwise from 20-80 mmHg. At the rim of the optic nerve head the vascular diameters as well as the intracapillary HbO(2)-values were stable till an intraocular pressure of 60 mmHg and decrease after IOP elevation to 70 and 80 mmHg. In contrast, in the center of the optic nerve head and in the choroid these parameters decline already from 40-50 mmHg on. At an IOP of 60 mmHg (P<0.01) and 70 mmHg (P<0.05) HbO(2)is significantly lower in the ONH center than at the rim. In the center and the choroid HbO(2)is well maintained between 20 and 40 mmHg. After pressure release at the end of the experiment HbO(2)increased to 94.3+/-4.6% (rim) and 98.8+/-1.5% (center) of the initial value at 20 mmHg (difference not significant).By the high spatial resolution of this new optical method we were able to demonstrate that the center of the optic nerve head is more sensitive to changes in intraocular pressure than the optic nerve head rim. Thus, tissue damage after critical haemodynamic and oxygenation parameters seems more probable in the relatively poor perfused center of the ONH than in the overperfused rim.

[The optic nerve disk in myopic children with elevated intraocular pressure]

The optic nerve disc of short-sighted children with elevated intraocular pressure was investigated to achieve early assessment of glaucoma and to detect signs which differentiate changes in the disc caused by short-sightedness from changes caused by glaucoma. The authors examined 16 eyes of 8 short-sighted children with elevated intraocular pressure. In addition to the basic ophthalmological examination they made a digital analysis of the optic nerve disc incl. planimetric evaluation of the dimensions of the disc, excavation and the neuroretinal rim. In two patients despite the higher intraocular pressure the area of the rim was supraliminal. In three patients the narrower area of the neuroretinal rim increased the probability of glaucoma In two patients with anisometropia on the eye with greater myopia the intraocular pressure was higher and the neuroretinal rim narrower as compared with the other eye. In one patient the area of the rim was very narrow and the diagnosis of glaucoma was confirmed also by arcuate scotoma in the lower part of the visual field corresponding to the narrow rim on top.

Correlation of pattern electroretinogram with optic disc cup shape in ocular hypertension

PURPOSE

To evaluate the correlation of pattern electroretinogram (PERG), an index of inner retinal function, with confocal scanning laser (CSLO) optic disc structural parameters in ocular hypertension (OHT).

METHODS

Thirty-four patients with OHT, normal white-on-white (Humphrey 30-2) perimetry, and normal clinical optic discs were examined with PERG and CSLO disc analysis. Two groups of normal subjects (n = 38 and 18, for PERG and CSLO, respectively) and a group of 12 patients with early open-angle glaucoma (EOAG) were also tested. Pattern electroretinogram amplitudes were measured in response to sinusoidal gratings of variable spatial frequency (0.58-5.8 cycles/degree), modulated in counter-phase at 7.5 Hz. Morphometric optic disc parameters were obtained by the Heidelberg Retina Tomograph (HRT), either globally or from predefined disc sectors. In addition to standard parameters, the cup shape measure, an index of depth variation and steepness of the cup walls, was determined.

RESULTS

In individual OHT patients, PERG amplitudes at 2.6 cycles/degree were negatively correlated with cup shape measures (r = -0.43, P < 0.01) obtained from analysis of the inferotemporal (IT) sector. No significant correlations were found for the other parameters. On average, the cup shape measures derived from IT sector or global analysis were significantly (P < 0.01) worse, and closer to the measures of EOAG patients, in OHT patients with abnormal PERG compared with those with normal PERGs. The cup shape measure displayed a low sensitivity (20%) and a high specificity (100%) in predicting PERG abnormalities in individual OHT patients.

CONCLUSIONS

The results indicate that in OHT there is a significant although weak correlation between PERG amplitude and the shape of the optic disc cup, suggesting a parallel involvement of both function and morphology. Combined PERG and optic disc cup structural analysis is of potential diagnostic value to detect early damage to optic nerve head in individual OHT patients.

Visual function correlates with nerve fiber layer thickness in eyes affected by ocular hypertension

PURPOSE

To test whether the high variability observed when measuring pattern electroretinogram (PERG), visual evoked potentials (VEP), and spatial contrast sensitivity (SCS) in eyes with ocular hypertension is associated with variation in nerve fiber layer thickness, as measured by optical coherence tomography (OCT).

METHODS

The study involved 32 untreated eyes (32 patients; age range, 29-64 years) showing a normal whiteon-white 24/2 Humphrey (San Leandro, CA) perimetry, IOP between 23 and 28 mm Hg, best corrected acuity of 20/20 or better, and none of the following papillary signs on conventional color stereo slides: rim notch(es), peripapillary splinter hemorrhages, or increased vertical-to-horizontal cup-to-disc ratio. On recruitment, each eye underwent SCS testing, OCT, PERG, and VEP recordings. Linear regression (Pearson's test) or Spearman's rank regression was adopted for the analysis of the data.

RESULTS

The 95% confidence limits of the electrophysiological data were: PERG P50 latency, 59.3 to 63 msec; PERG P50 to N95 amplitude, 0.74 to 1.15 cmV; VEP P100 latency, 113 to 118 msec; VEP N75 to P100 amplitude, 3.81 to 4.90 micromV. The 360 degrees nerve fiber layer thickness overall (NFLO) ranged between 113 and 169 microm (145+/-16 microm; mean+/-SD) and significantly correlated with PERG P50 to N95 amplitude (r: 0.518; P = 0.002), PERG P50 latency (r: -0.470; P = 0.007), VEP N75 to P100 amplitude (r: 0.460; P = 0.008), VEP P100 latency (r = -0.422; P = 0.016) and SCS at 3 cyc/deg (r: -0.358; P = 0.044).

CONCLUSIONS

The variability of PERG, VEP, and SCS testing observed in eyes with ocular hypertension is associated with differences in NFL thickness (the thinner the layer, the worse the visual function).

Correlation of functional and structural measurements in eyes suspected of having glaucoma

PURPOSE

This study was conducted to determine the correlation between structural changes in the retinal nerve fiber layer (RNFL) and functional loss detected on short-wavelength automated perimetry (SWAP) in a population of patients with suspected glaucoma.

METHODS

With a selection criteria of intraocular pressure (IOP) more than 21 mmHg and normal results of conventional automated perimetry, 49 eyes of 49 patients with ocular hypertension were enrolled in the study. The SWAP was performed with a modified Humphrey field analyzer, and visual field indexes (mean deviation [MD], corrected pattern standard deviation [CPSD]) were calculated. Semiquantitative RNFL scores were given separately to diffuse and localized defects of the RNFL.

RESULTS

The MD increased significantly with higher diffuse and total RNFL scores, with good correlation coefficients. A weak correlation was found between CPSD and diffuse, total, and localized RNFL scores.

CONCLUSION

Diffuse RNFL loss are associated with abnormalities in visual field indexes (MD), whereas focal structural damage showed no correlation with visual field loss.

Ciliary body melanocytoma with anterior segment pigment dispersion and elevated intraocular pressure

PURPOSE

To discuss a case in which melanocytoma of the ciliary body presented with widespread pigment dispersion and elevated intraocular pressure (IOP).

METHODS

A 64-year old woman presented with increased IOP and persistent anterior segment inflammation in her right eye. She had undergone a trabeculectomy for uncontrolled IOP before presentation. Slit-lamp examination, gonioscopy, and ultrasound biomicroscopy revealed a ciliary body mass with extension into the subconjunctiva in addition to widespread pigmentary dispersion in the anterior segment. Enucleation of the right eye was performed for histopathologic evaluation, as a diagnosis of ciliary body melanoma was made on clinical examination.

RESULTS

Histopathologic findings were diagnostic of a melanocytoma of the ciliary body with necrosis and focal malignant transformation with extension of melanocytoma cells and melanophages into the subconjunctival space, trabecular meshwork, and anterior chamber angle.

CONCLUSION

Melanocytoma of the ciliary body is a rare intraocular tumor that may present with pigment dispersion and secondary elevated IOP. Careful examination of the anterior segment is imperative in such cases.