Abstract
Purpose :
Controversy exists regarding the role of eye oscillations in degrading visual acuity in infantile nystagmus (IN). These have important implications for treatments aimed at improving vision in IN by reducing nystagmus. We take advantage of changes in nystagmus occurring in IN when maintaining different gaze angles to explore within- and between-subject differences in nystagmus in relation to visual acuity (VA). The effect of retinal deficits were also compared using optical coherence tomography (OCT).
Methods :
Nystagmus (EyeLink, SR Research) and distance VA were recorded at 7 different horizontal gaze angles (at 10° intervals) in 46 participants with IN. Nystagmus intensity and expanded nystagmus acuity function (NAFX) were calculated for each gaze angle.Only participants with nystagmus intensity ranges >33.3% of mean intensity / NAFX were included (16 Idiopathic, 21 albinism, 6 retinal disease). Foveal hypoplasia was assessed using OCT B-scan images through the foveal center. Regression analysis was used to estimate within-subject measures of r, slope and intercept for each participant. Linear mixed models were used to explore within- and between-subject factors by including mean intensity or NAFX in the model.
Results :
Between-subject measures (i.e. mean) of intensity and NAFX were not significant predictors of VA in statistical models for any of the three disease groups (p>0.1). In contrast, within subject repeated measures of intensity and NAFX measures were mostly significant (p=0.001 and 0.15 for idiopaths, 0.001 and 0.001 for albinism, 0.06 and 0.03 for retinal diseases for intensity and NAFX, respectively). However, individual slopes were shallow and showed a wide degree of variation (e.g. mean±SD=0.036±0.029 and 0.037±0.076 change in logMAR lines for every 1°/s change in nystagmus intensity, for idiopaths and albinism, respectively).
Conclusions :
We find that within-subject changes in nystagmus intensity and foveation are strongly associated with VA concluding that nystagmus oscillations can play a role in degrading VA. However, slopes of within subject nystagmus measures show high variability with average values indicating that a large change in nystagmus is necessary to effect a relatively small change in VA (e.g. in idiopaths and albinism >25°/s mean difference in intensity is required to cause a change of 1 logMAR line, where the mean intensity = 18°/s)
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.