Scotoma Visibility and Reading Rate with Bilateral Central Scotomas.

PURPOSE: In this experiment, we tested whether perceptually delineating the scotoma location and border with a gaze contingent polygon overlay improves reading speed and reading eye movements in patients with bilateral central scotomas. METHODS: Eight patients with age-related macular degeneration and bilateral central scotomas read aloud MNRead style sentences with their preferred eye. Eye movement signals from an EyeLink II eyetracker were used to create a gaze contingent display in which a polygon overlay delineating the area of the patient's scotoma was superimposed on the text during 18 of the 42 trials. Blocks of six trials with the superimposed polygon were alternated with blocks of six trials without the polygon. Reading speed and reading eye movements were assessed before and after the subjects practiced reading with the polygon overlay. RESULTS: All of the subjects but one showed an increase in reading speed. A paired-samples t-test for the group as a whole revealed a statistically significant increase in reading speed of 0.075 ± 0.060 (SD) log wpm after reading with the superimposed polygon. Individual subjects demonstrated significant changes in reading eye movements, with the greatest number of subjects demonstrating a shift in the average vertical fixation locus. Across subjects, there was no significant difference between the initial and final reading eye movements in terms of saccades per second, average fixation duration, average amplitude of saccades, or proportion of non-horizontal saccades. CONCLUSIONS: The improvement in reading speed (0.075 log wpm or 19%) over the short experimental session for the majority of subjects indicates that making the scotoma location more visible is potentially beneficial for improving reading speed in patients with bilateral central scotomas. Additional research to examine the efficacy of more extended training with this paradigm is warranted.

Repeatability of Nidek MP-1 Fixation Measurements in Patients With Bilateral Central Field Loss.

PURPOSE: Visual performance in patients with bilateral central field loss is related to fixation stability. This study evaluated the repeatability of visual-fixation parameters in patients with bilateral central field loss, measured with the MP-1 microperimeter for fixation durations on the order of 15 to 30 seconds. METHODS: Bivariate contour ellipse area (BCEA), and the eccentricity and meridian of the preferred retinal locus (PRL) were determined in 56 eyes of 56 patients, sampled at two investigational sites. Repeatability and agreement were assessed by estimating 95% limits of agreement for each parameter from two fixation examinations conducted on the same day. RESULTS: The 95% confidence intervals (CI) for log BCEA and for PRL eccentricity and meridian were ±0.67 log deg2, ±2.0°, and ±65.9°, respectively. Each CI decreased substantially if a small number of outlying data points were excluded. For all parameters, the mean difference between the two fixation examinations was close to zero. CONCLUSIONS: For most patients with bilateral central field loss, the repeatability of estimated BCEA and PRL eccentricity and meridian is good. When repeated estimates of fixation parameters do not agree, the absence of a well-developed PRL or the use of multiple PRLs may be suspected.

Fixation locus in patients with bilateral central scotomas for targets that perceptually fill in.

PURPOSE: In this experiment, we investigated whether target type affects the retinal fixation location and stability in patients with bilateral central scotomas and, specifically, whether targets expected to perceptually fill in are imaged at or near the vestigial fovea. METHODS: The retinal location and stability of fixation were measured using the Nidek MP-1 microperimeter in 12 patients with bilateral central scotomas for six types of fixation target, three expected to fill in and three that included letters. The approximate position of the vestigial fovea was delineated in 10 of the patients either by using residual retinal landmarks or by locating the residual foveal pit in a dense macular scan obtained with a Spectralis optical coherence tomographer. Fixation location and stability were compared for the different target types and referenced to the position of the vestigial fovea. RESULTS: All of the subjects except one fixated consistently on targets that included a letter using peripheral retinal locations outside of the central scotoma. Eleven of the 12 subjects used a retinal location closer to the vestigial fovea to fixate targets expected to fill in compared with letters. Although four of the subjects imaged the filled-in targets at or within a half degree of the vestigial fovea, six other subjects imaged the filled-in targets at a retinal locus removed from the vestigial fovea. Target type produced no overall significant difference in fixation stability, specified in terms of bivariate contour ellipse area. However, in some individual subjects, fixation tended to be more stable on letter targets than on filled-in targets. CONCLUSIONS: In patients with central field loss, letter targets generate more consistent fixation behavior than filled-in targets and should be used for eccentric viewing training and perimetry.