Night vision and glare vision thresholds and recovery time in myopic and hyperopic eyes

Abstract

The purpose of this study was to compare night vision and glare vision thresholds and recovery times in myopic and hyperopic eyes. Using a Night Sight Meter, these three parameters were measured in 44 myopic and 44 hyperopic eyes of Black male subjects age-matched 20.8 years ± 1.67 and 21.6 years ± 1.05 old respectively and compared. Thresholds were measured first by assessing the eye’s ability to see under conditions of low illumination and in the presence of a glare source. Glare recovery time was determined by measuring the minimum time neededto adjust to low levels of light illumination after exposure to a glare stimulus. Descriptive, two-sample t-test and Pearson correlation statistics were used to analyze and compare the sets of data from the two groups. The mean refractive error in the myopic eyes was –2.15 D ± 1.41 (range = –0.50 D to –4.50 D) and 1.76 D ± 1.22 (range = 0.50 D to 4.00 D) in the hyperopic group. The mean night vision thresholds for the myopic eyes was 32 cd/m2 ± 4.69 (range = 23 cd/m2 to 42 cd/m2) and 28.97 cd/m2 ± 4.90 (range = 18 cd/m2 to 37 cd/m2) for hyperopic eyes. The difference between the mean night vision thresholds of the myopic and hyperopic eyes wasstatistically significant (p < 0.05). For glare vision threshold, the mean for myopic eyes was 64 cd/m2 ± 5.81 (range = 53 cd/m2 to 78 cd/m2), while the mean for hyperopic eyes was 44.84 cd/m2 ± 5.69 (range = 32 cd/m2 to 59 cd/m2). Also, the difference between the mean glare vision thresholds of the myopic and hyperopic eyes was statistically significant (p < 0.05). The recovery times ranged from 0.45 s to 3.10 s for the myopic eyes and 0.30 s to 2.25 s for the hyperopic eyes. The mean glare recovery time for the myopic eyes (mean = 1.41 s ± 0.77) was significantly longer (p < 0.05) than the times for hyperopic eyes (mean = 1.04 s ± 0.65). There was a significant positive correlation between recovery times and the magnitude of myopia (r = 0.93, p < 0.05) while the relationship between recovery times and the magnitude of hyperopia was significantly negatively correlated (r = –0.76,  p < 0.05). These findings suggest that myopic persons would have more difficulty seeing under conditions of low illumination and in the presence of glare than hyperopic eyes. This could probably be due to aberrations resulting from larger pupils in the myopic eyes. (S Afr Optom 2010 69(3) 132-139)