Purpose
To determine visual field features of high myopic eyes with different levels of refractive errors in a Chinese population.
Methods
This retrospective comparative study included 452 eyes with high myopia (>-6D) and 108 emmetropic eyes (+0.5 to -0.5D). Eyes with abnormalities other than myopic retinal changes were excluded. Eyes with high myopia were further categorized into three subgroups based on the spherical equivalents (SE) of refractive errors: -6D to -10D (group 1, n=238), -10D to -15D (group 2, n=124) and >-15D (group 3, n=90). Central 30 degree visual field was tested by automatic perimeter Octopus 101 with Low vision central (LVC) program. Outcome were assessed by mean sensitivity (MS) and average number of defects of the visual field. The data were analyzed by t-test for high myopic and normal eye comparison, and Analysis of variance (ANOVA) and Tukey’s test for comparison between subgroups.
Results
The MS of high myopic eyes was significantly reduced comparing to emmetropic eyes (27.96±5.38 vs 34.05±2.29 dB, P<0.001). The MS in subgroup 1, 2 and 3 were 29.33±5.35dB, 27.57±4.50 dB and 24.84±5.22 dB, respectively (P<0.001; Tukey’s test p<0.05 between each two groups). The average number of defects was 0.88±3.42 in high myopia group and 0.04±0.39 in emmetropia group (P<0.001). While not statistically significant, subgroup showed a trend of increased average number of defects with increased myopia (group 1: 0.79±3.43, group 2: 0.80±3.36, group 3: 1.21±3.50; P=0.584).<br /> Of 85 eyes in the high myopia group younger than 20 years old, 19 eyes (22%) demonstrated temporal enlargement of blind spot, which was not correspondent to the myopic temporal crescent (Fig. 1, 2). Their bio-parameters were significantly different from rest of the eyes in the same age group, including visual acuity (0.39±0.27 vs 0.87±0.3, P<0.05), SE (-15.54±2.98D vs -7.74±3.07D, P<0.05), and axial length (29.8±1.8mm vs 26.73±1.28mm, P<0.05).
Conclusions
The results of this study suggested high myopic eyes had decreased central visual field qualities. The central 30 degree visual field sensitivity declined as the refractive error increased. An unusual visual field pattern with temporal enlargement of the blind spot was found in a subgroup of younger high myopes and associated with higher refractive errors. This pattern may indicate early impairment of retina nasal to the optic nerve in extremely high myopic eyes.