Importance of two-dimensional gaze analyses in the assessment of reading performance in patients with retinitis pigmentosa

The causes of reading difficulties in people with peripheral visual field loss are not fully understood. We conducted a two-dimensional gaze analysis on eye movements during reading in patients with retinitis pigmentosa to investigate the causes of reading difficulties in relation to the central visual field using a binocular eye mark recorder (EMR-9). Twenty-seven patients with retinitis pigmentosa whose central visual field narrowed to ≤ 20° using Goldmann kinetic perimetry (I/4 target) and this present study included eight healthy participants. The participants’ visual acuities were corrected to better than +0.4 logMAR. Correlations and multivariate regression analyses were investigated between the number of letters read correctly, the I/4 central visual field, V/4 perifoveal and peripheral visual field, and visual acuity. Multivariate regression analysis revealed that all these parameters played almost equal roles in the number of letters read correctly. In the two-dimensional gaze analysis, the task performance time of patients during reading increased as the I/4 central visual field narrowed. The task performance time was more clearly correlated with the rotation saccade (r = 0.428, p <0.05) and the distance of the vertical direction (ΣY) of eye movements (r = 0.624, p < 0.01), but not with regressive saccade and the distance of the horizontal direction (ΣX). Visual acuity was correlated with the task performance time (-0.436, <0.05) but not with eye movement directionality. Reading difficulties in patients with retinitis pigmentosa result from impaired eye movement directionality. Understanding eye measurements for people with tunnel vision required a two-dimensional gaze analysis. The two-dimensional gaze analysis also showed that the involvement of the perifoveal and peripheral visual fields, visual acuity, and I/4 central visual field was important for reading in people with tunnel vision.