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.

Reproducibility of retardation measurements with the nerve fiber analyzer II.

PURPOSE: To evaluate the reproducibility of a scanning laser polarimeter, the Nerve Fiber Analyzer II (NFA II, Laser Diagnostic Technologies, San Diego, CA, U.S.A.). METHODS: Five independent retardation maps of the peripapillary retina of five normal eyes were acquired by three experienced operators (including V.S.G.) on each of three separate days for a total of 45 retardation maps per patient. Two methods of image processing, one using a baseline image and another using the individual scans, were used to compare the reproducibility of three summary measures, average retardation, integral, and retardation ratio. RESULTS: The average standard deviation (and its 95% confidence interval) of average retardation within a 10-pixel-width-band of the 9 baseline images was 0.43 degree (0.36-0.51 degree) with a mean coefficient of variation of 4.2% (3.8-4.5%). In a random effects model, each of the three retinal nerve fiber layer (RNFL) summary measures varied significantly by patient (p < 0.016), but not by operator (p > 0.19), or operator by patient interaction (p > 0.524). In addition, there was small, but statistically significant day-by-operator-within-patient (intraobserver) variation in the random effects model. CONCLUSIONS: These results suggest that the NFA II provides reproducible measurements and that, on average, measurements obtained by separate operators on different days are similar.

Change in optic disk topography after trabeculectomy.

PURPOSE: To investigate the relationship between optic disk topography and intraocular pressure before and after trabeculectomy with confocal scanning laser ophthalmoscopy. METHODS: The eyes of 49 consecutive patients undergoing trabeculectomy at a university-based glaucoma practice underwent preoperative and postoperative imaging using a confocal scanning laser ophthalmoscope (Heidelberg Retina Tomograph). Three images of one eye of each patient were obtained with a 15-degree field of view. Preoperative images were obtained approximately 2 months before surgery (mean +/- SD, 2.4 +/- 1.6 months). Postoperative images were obtained at least 3 months after surgery (mean, 4.5 +/- 2.6 months). RESULTS: Mean preoperative intraocular pressure, postoperative intraocular pressure, and percent change in intraocular pressure respectively were 23.1 +/- 6.8 mm Hg, 12.7 +/- 7.1 mm Hg, and 43.8% +/- 29.9%. A significant association (P < .01) was found between percent decrease in intraocular pressure and decreases in cup area, cup volume, and cup/disk area ratio as well as between percent decrease in intraocular pressure and increases in rim area, rim volume, mean height contour, retinal cross-section area, and height in contour. Between 11.7% and 31.2% of the variability (R2) in these parameters was explained by the percent change in intraocular pressure. Topography changes were more strongly associated with percent change than with mean change in intraocular pressure. We found no association between percent decrease in intraocular pressure and reference plane height or maximum cup depth. CONCLUSIONS: Changes in optic nerve topography were associated with reduction in intraocular pressure after trabeculectomy.

Association between quantitative nerve fiber layer measurement and visual field loss in glaucoma.

PURPOSE: To evaluate the association between quantitative nerve fiber layer measurements and visual field loss in patients with primary open-angle glaucoma. METHODS: Quantitative retinal nerve fiber layer measurements were obtained in 53 patients with primary open-angle glaucoma by using confocal scanning laser ophthalmoscopy (cross-section area) and confocal scanning laser polarimetry (retardation ratio). For each eye, three images were obtained with each instrument. An image that was the mean of those three was created and used in all analyses. We investigated the association between global, regional, and hemifield differences in retinal nerve fiber layer measurements and visual field loss with linear regression techniques. RESULTS: The retardation ratio decreased with increasing mean visual field loss, measured both globally and regionally; R2 (the amount of variation explained by the model) ranged from 8% to 21%. Retinal nerve fiber layer cross-section area was not significantly associated with global measures of visual field loss. The inferior visual field mean deviation increased with decreasing superior retinal nerve fiber layer cross-section area (R2 = 8.2%, P = .04); superior visual field mean deviation was not associated with inferior retinal nerve fiber layer cross-section area (R2 = 2.6%, P = .25). Hemifield differences in visual field mean deviation increased with increasing hemifield differences in retinal nerve fiber layer cross-section area (R2 = 20.0%, P < .001), but not with retardation ratio (R2 = 0.9%, P = .48). CONCLUSIONS: Quantitative measures of the retinal nerve fiber layer using both confocal scanning laser ophthalmoscopy and confocal scanning laser polarimetry were correlated with visual field loss in glaucoma patients.

Correlation of peripapillary retinal height and visual field in glaucoma and normal subjects.

PURPOSE: To investigate the relationship between peripapillary retinal height and visual field sensitivity. PATIENTS AND METHODS: Fourteen normal subjects and 25 primary open-angle glaucoma patients were examined using a confocal scanning laser ophthalmoscope (Heidelberg Retina Tomograph). Visual fields (Humphrey program 24-2) were assessed with both standard achromatic automated perimetry and shortwavelength automated perimetry. The mean peripapillary retinal height was determined for superotemporal (60-90 degrees ), superonasal (91-120 degrees ), inferotemporal (271-300 degrees ), and inferonasal (240-270 degrees ) sectors. Based on Glaucoma Hemifield Test sector definitions, achromatic automated perimetry and short-wavelength automated perimetry fields were divided into each of four distinct regions. RESULTS: Significant differences in disc rim area, rim-disc area ratio, cup volume, and each papillary region were found between glaucoma patients and normal subjects. With both standard achromatic automated perimetry and short-wavelength automated perimetry, significant correlations (p < 0.05) were found between the mean peripapillary retinal height of the inferotemporal, inferonasal, superotemporal, and superonasal sectors and age-adjusted mean deviation of their respective anatomically matched visual field region. In addition, peripapillary retinal height was more highly correlated with ageadjusted mean deviation than disc rim area in glaucoma patients. CONCLUSIONS: We found that peripapillary height, particularly in the temporal region, showed the strongest association with visual field loss in glaucoma patients.

Ethnic differences in optic nerve head topography.

PURPOSE: To investigate ethnic differences in optic nerve head topography. METHODS: This is a cross-sectional university-based comparative study of 180 normal subjects (43 African-American, 45 Asian, 48 Hispanic, and 44 white subjects) ages 19-40 years. Optic nerve head parameters including optic disc size, cup-disc ratio, rim area, rim volume, cup volume, and maximal cup depth were measured using a confocal scanning laser ophthalmoscope (Heidelberg Retina Tomograph). Differences among groups were evaluated using analysis of variance. RESULTS: Disc area, cup volume, maximal cup depth, and vertical cup-disc ratio were largest in African-Americans, intermediate in Asians and Hispanics, and smallest in whites; for these parameters the differences between African-Americans and whites were statistically significant. Significant differences were also found between African-Americans and Hispanics for cup volume, and between African-Americans and Asians for vertical cup-disc ratio and maximal cup depth. Rim volume and rim area were not significantly different among the four ethnic groups. CONCLUSIONS: Ethnic differences in the normal optic nerve are present and should be taken into a ccount when evaluating the optic disc for glaucoma and other optic neuropathies.