Fixation patterns and reading rates in eyes with central scotomas from advanced atrophic age-related macular degeneration and Stargardt disease

Abstract

Purpose: To study fixation patterns and reading rates in eyes with central scotomas from geographic atrophy (GA) of age-related macular degeneration and to compare fixation patterns with those of patients with Stargardt disease.

Methods: Scanning laser ophthalmoscope analysis of fixation patterns in eyes with 20/80 to 20/200 visual acuity. Included were 41 eyes of 35 patients with GA and 10 eyes of 5 patients with Stargardt disease. The patients with GA also were tested for maximum reading rate, and the size of the areas of atrophy were measured by fundus photograph analysis.

Results: Sixty-three percent of GA eyes fixating outside the atrophy placed the scotoma to the right of fixation in visual field space, 22% placed the scotoma above fixation, and 15% placed it to the left, regardless of the laterality of the GA eye. Fixation was stable in subsequent years of testing for scotoma placement to the right of or above fixation. All GA eyes fixated immediately adjacent to the atrophy. In contrast, seven of ten eyes with Stargardt disease fixated at a considerable distance from the scotoma border, with the dense scotoma far above the fixation site in visual field space. For the patients with GA, the maximum reading rate was highly correlated with size of the atrophic area, but not with age or visual acuity within the limited visual acuity range tested. There was a trend to more rapid reading with the scotoma above fixation and slower reading with the scotoma to the left.

Conclusion: There is a preference for fixation with the scotoma to the right in eyes with GA. Patients with Stargardt disease use different strategies for fixation, perhaps due to subclinical pathology adjacent to the atrophic regions. The size of the atrophic area in GA plays the predominant role in reading rate for eyes that have already lost foveal vision.

Figure 1

Right eye. Visual acuity was 20/145. A, fluorescein angiography at baseline shows a large, discrete, hyperfluorescent area corresponding to the central geographic atrophy, measured as 8.4 disc areas in size. B, in scanning laser ophthalmoscope (SLO) testing, fixation was placed so that the area of atrophy was immediately to the right of fixation. There was a dense scotoma corresponding to the atrophy. In the SLO image, the thick white cross is the fixation target for the patient. The black cross is not seen by the patient. Open symbols = an area with a dense scotoma; closed symbols = a seeing area. The narrower cross is used for landmark registration. On the fluorescein angiographic images, the arrow indicates the site of fixation as determined by SLO testing.

Figure 2

Left eye. Visual acuity was 20/145. A, fluorescein angiography at baseline shows a large discrete hyperfluorescent area corresponding to the central geographic atrophy, measured as 2.3 disc areas in size. B, in scanning laser ophthalmoscope (SLO) testing, fixation is placed so that the atrophy is immediately to the right. There is a dense scotoma corresponding to the central atrophy and to the peripapillary atrophy. Fixation is placed with the central scotoma to the right, despite the limiting peripapillary atrophy to the left. In the SLO image, the thick white cross is the fixation target for the patient. The black cross is not seen by the patient. The open symbols indicate an area with a dense scotoma, whereas closed symbols indicate a seeing area. The narrower cross is used for landmark registration. On the fluorescein angiographic images, the arrow indicates the site of fixation as determined by SLO testing.

Figure 3

Left eye of a 12-year-old girl with Stargardt disease. Visual acuity was 20/107. A, fluorescein angiography shows a central atrophic hyperfluorescent lesion and a dark choroid. B, on scanning laser ophthalmoscope (SLO) testing, there was a dense scotoma, bounded by the arrowheads, corresponding to the hyperfluorescent area on the fluorescein angiogram. However, fixation was placed 2° superior to the margin of the dense scotoma, near the arcade vessel (marked an an arrow in Fig 3A). Letter and word reading were performed at the indicated site of fixation. In the SLO image, the thick white cross is the fixation target tor the patient. The black cross is not seen by the patient. Open symbols = an area with a dense scotoma; closed symbols = a seeing area. The narrower cross is used for landmark registration. On the fluorescein angiographic images, the arrow indicates the site of fixation as determined by SLO testing.

Figure 4

Left eye of an 18-year-old woman with Stargardt disease. Visual acuity was 20/132. A, the fundus photograph shows a poorly defined central atrophic lesion, surrounded by flecks. B, scanning laser ophthalmoscope (SLO) testing shows a central dense scotoma, with fixation nearly 4° above the superior border of the dense scotoma (arrowhead). Fixation is superior to the arcade vessel (marked by arrow on fundus photograph). Letter and word reading were performed at the indicated site of fixation. In the SLO image, the thick white cross is the fixation target for the patient. The black cross is not seen by the patient. Open symbols = an area with a dense scotoma; closed symbols = a seeing area. The narrower cross is used for landmark registration.

Figure 5

Maximum reading rate versus visual acuity. For the visual acuity range of this study (20/80–20/200, inclusive), the visual acuity accounts for less than 1% of the variability in reading rate.

Figure 6

The maximum reading rate in words per minute as a function of size of the atrophic area (in millimeters square on the retina). The equivalent in Macular Photocoagulation Study disc areas is given at the top of the graph. Expressing size as the square root of area makes the distribution most normally distributed. There is a very strong inverse correlation of reading rate with square root of atrophic area (r = 0.75 for all eyes). Open symbols = eyes in which fixation was placed within the atrophy (either unseen on atrophic regions, or in clear regions); closed symbols = eyes that fixated outside the atrophy (r = 0.76).