Relationship of optic disc topography to optic nerve fiber number in glaucoma

OBJECTIVE

To assess the relationship between in vivo measurements of optic disc topography and histomorphometric measurements of optic nerve fiber number in glaucoma.

METHODS

Both eyes of 10 monkeys (Macaca fascicularis) with laser-induced glaucoma in the right eye were studied. Optic disc topography was measured in vivo with a confocal scanning laser ophthalmoscope. Histomorphometry was performed on optic nerve cross sections using bright-field microscopy with camera lucida. Nerve fiber density was estimated by unbiased random sampling. Nerve fiber number was estimated for each sector by multiplying nerve fiber density with neuroglial area. Nerve fiber count was compared with each of 13 global optic disc topographic parameters.

RESULTS

For neuroretinal measurements in the glaucomatous eyes, rim area, retinal nerve fiber layer (RNFL) cross-sectional area, rim volume, and RNFL thickness correlated significantly with optic nerve fiber number. Differences in nerve fiber count between control and glaucomatous optic nerves showed the strongest correlation with differences in mean height contour; this was followed by RNFL cross-sectional area, RNFL thickness, rim volume, and differences in rim area. For cup measurements in the glaucomatous eyes, cup volume below reference, cup area, mean cup depth, the ratio of cup area to disc area, and cup shape correlated significantly with nerve fiber number. Differences in nerve fiber number between control and glaucomatous optic nerves showed the strongest correlation with differences in cup shape; this was followed by mean cup depth, cup volume below reference, the ratio of cup area to disc area, cup area, and differences in cup volume below surface. No association was found between optic nerve fiber number and optic disc area in glaucomatous eyes.

CONCLUSIONS

In experimental glaucoma, most optic disc topography measures correlated significantly with optic nerve fiber number. The results of this histomorphometric study support the use of confocal scanning laser ophthalmoscopy to evaluate optic nerve damage in glaucoma.

Effect of cataract and pupil size on image quality with confocal scanning laser ophthalmoscopy

OBJECTIVE

To determine the effect of pupil size and cataract on the reproducibility and image quality obtained with confocal scanning laser ophthalmoscopy.

METHODS

Three image series were obtained with a confocal scanning laser ophthalmoscope (Heidelberg Retina Tomograph, Heidelberg, Germany) before and after pupillary dilation in each of 39 subjects (8 normal subjects, 5 glaucoma suspects, and 26 patients with glaucoma). The cataract density was measured with both a lens opacity meter and the Lens Opacities Classification System III system. The image quality of each image series was subjectively scored on a scale of 0 (poor) to 9 (high) by 2 independent observers who were unaware of the cataract density and pupil size during image acquisition. The image quality and reproducibility were objectively evaluated using the SD of the mean topography image of each subject.

RESULTS

The mean pupil diameter in all subjects before and after dilation was 2.5 +/- 0.8 mm and 5.8 +/- 1.4 mm, respectively. After pupillary dilation, both the mean image quality score and mean SD of the mean topography image improved (from 4.5 +/- 3.5 to 7.4 +/- 2.3 and from 48.6 +/- 18.8 microns to 35.6 +/- 15.5 microns, respectively). The quality score of the images that were obtained before pupillary dilation was associated with the pupil size and density of nuclear and posterior subcapsular cataracts. The SD of the mean topography images that were obtained before pupillary dilation increased with a decreasing pupil size (P = .003) and an increasing density of the nuclear (P < .03), cortical (P = .02), and posterior subcapsular (P = .002) opacity.

CONCLUSIONS

Although pupillary dilation improved the image quality in most subjects, the improvement was sometimes small. Those subjects with small undilated pupils and/or cataracts may benefit most from pupillary dilation.

Indocyanine green angiography of the peripapillary region in glaucomatous eyes by confocal scanning laser ophthalmoscopy

PURPOSE

To investigate the peripapillary region in glaucomatous eyes by indocyanine green angiography.

METHODS

Indocyanine green angiography of the optic disk and peripapillary region was evaluated by modified confocal scanning laser ophthalmoscopy in 22 eyes of 22 patients with glaucoma and in 10 normal eyes of 10 control patients with unilateral choroidal melanoma. The occurrence and extent of indocyanine green angiographic anomalies were correlated with optic disk morphology and the severity of glaucoma.

RESULTS

In the 32 eyes of 32 patients, two types of peripapillary defects were identified in the late-phase angiograms. The first was hypofluorescent areas in the peripapillary region and was more common in eyes with glaucoma (P < .02); their occurrence and extent correlated with age (P < .01). In nine of the 17 eyes, alpha (peripheral) zone peripapillary atrophy corresponded with the areas of peripapillary indocyanine green hypofluorescene. The second defect, hypofluorescent halos adjacent to and extending around the full circumference of the optic disk margins, did not correlate with any of the study factors.

CONCLUSIONS

Indocyanine green angiography showed areas of hypofluorescene in the peripapillary region in late-phase angiograms in 68% of glaucomatous eyes compared with 20% of control eyes. These hypofluorescent areas might be either of result of blockage of background fluorescence by pigment or caused by an absence of vascular tissue (choriocapillaris).

Optic nerve head topography in ocular hypertensive eyes using confocal scanning laser ophthalmoscopy

PURPOSE

To compare measurements of optic nerve topography of ocular hypertensive patients with those of normal subjects and primary open-angle glaucoma patients.

METHODS

Three age-matched study groups of 46 ocular hypertensive patients, 46 primary open-angle glaucoma patients, and 46 normal subjects were recruited from patients and volunteers of a glaucoma referral practice. Optic nerve topography was measured using a confocal scanning laser tomograph, the Heidelberg Retina Tomograph. The following optic nerve parameters were evaluated: disk area, cup/disk area ratio, cup shape, height in contour, rim area, rim volume, maximum cup depth, cup area, cup volume, retinal height, and retinal cross-section area. For this cross-sectional study, analysis of variance was used to evaluate overall differences among the three subject groups and the Tukey-Kramer multiple comparison test to evaluate differences between the means of two groups.

RESULTS

Statistically significant differences among study groups were found for all topographic optic nerve parameters evaluated. Despite considerable overlap in optic nerve parameter measurements among the study groups, mean values of ocular hypertensive eyes were intermediate between those for normal and primary open-angle glaucoma eyes. Statistically significant differences were found between ocular hypertensive and glaucomatous eyes for all optic nerve parameters measured, and between ocular hypertensive and normal eyes for disk area, height in contour, rim area, and rim volume.

CONCLUSIONS

In age-matched groups, mean measurements of certain topographic optic nerve parameters of ocular hypertensive eyes differ from those of normal and glaucomatous eyes.