Anatomical and fixation parameters as predictors of reading speed (RS) in Stargardt Disease

Abstract

Purpose : Stargardt Disease (STGD1) is a juvenile macular degeneration characterized by central vision loss and expanding areas of atrophic lesions (AL). Research indicates that visual acuity (VA) is weakly or not correlated with (w/) AL areas. We hypothesize that RS is not correlated w/ AL areas, but that the distance preferred retinal locus to fovea centralis (PRL-F), quality of fixation, and VA may better predict RS.

Methods : As part of a prospective clinical trial, 50 STGD1 subjects w/ ABCA4 mutations and well-delineated AL underwent RS w/ International Reading Speed Texts, a set of standardized sentences size 10pt designed to mimic real-life reading. Text #1 (156 English words, 236 words/minute [wpm] healthy controls) was read out loud using binocular vision and visual aids under office lighting. One illiterate subject was excluded from the data. Autofluorescence imaging was performed and AL area measured using built-in calipers. Fixation parameters were acquired on microperimeter (Nidek) MP1 during 10-2 testing, quality of fixation determined by Fuji classification (stable, SF; relatively unstable, RUF; unstable, UF). Statistics were performed using a 2-tailed t-test. Analyses used the better eye, defined by eye w/ better VA if difference between eyes was 2+ lines, otherwise by eye w/ shorter PRL-F distance.

Results : Mean RS among subjects was 106 wpm (±50 SD), 55% slower than normal controls (p<0.01). There was a significant effect of fixation stability on RS: subjects w/ SF and RUF read 66 (p<0.01) and 40 (p~0.05) wpm faster, respectively, than those w/ UF. Unsurprisingly, VA was strongly associated w/ RS (r~0.6): subjects w/ VA>20/40 read 134 wpm avg (28-199); decrease of 3 VA lines correlated with decrease of ~22 wpm RS.

Subjects w/ PRL-F of <3 or >5° read on average 117 wpm (27-199) or 84 wpm (12-161, p=0.03), respectively. An increase in PRL-F of 1° was moderately associated w/ 5.9 wpm decrease in RS (r~0.4) (Fig 1). All subjects w/ SF had PRL-F of <3°, while all subjects w/ UF had PRL-F>4°.

All correlations between reading speed and various parameters showed no or weak correlation w/ reading speed, including AL area (Fig 2).

Conclusions : Data confirm the hypothesis that quality of fixation, PRL-F distance, and VA are predictive of RS, and that AL area and other presented clinical factors are not. Quality of fixation and PRL-F may be used as predictive factors of visual function in STGD1.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

Fig 1

 

Fig 2