Dynamics of Monocular Blur Driven Accommodation in Children and Young Adults

Abstract

Purpose:: The main sequence of accommodation (MS of ACC) plots peak velocity as a function of amplitude. Recently, it has been suggested that the shape of the MS of ACC changes with age. Young adults (22 -23 yrs) showed a steeper main sequence compared to older adults (38-42 yrs) ¹. This study examines the main sequence of accommodation in school aged children.

Methods:: A total of 15 individuals comprising of 5 young adults (mean age=27.8±1.63 yrs), 5 older children (Mean age = 10.2±1.64 yrs) and 5 young children (mean age = 6.4±0.5yrs) participated in the study. Monocular accommodative responses were recorded by a digital high speed photorefractor at 75Hz while participants changed focus from a high contrast target fixed at 1m to three different near positions (2, 3 and 4D amplitude). Response dynamics were analyzed offline using image analysis software (Image Pro Plus, Media Cybernetics). The functions best describing, MS of ACC, peak acceleration and latency were defined by curve fitting (Prism, GraphPad Inc.) and compared between the three groups.

Results:: For all groups, the MS of ACC was best described by an exponential relationship (Young children: y=13.36*(1-exp^(-0.59x)), R²=0.28; Older children: y=16.77*(1-exp^(-0.25x)), R²=0.53; Adults: y=13.82*(1-exp^(-0.32x)), R²=0.39). Statistical comparisons of the curve fits between groups showed that the MS of ACC for young children was significantly steeper compared to older children and adults (F_(4,162)=10.67, p<0.0001). Peak acceleration of accommodation as a function of response amplitude remained constant for all groups (Young children, y=11.04x+115.2, R²=0.01, p>0.05; Older children, y=8.06x+62.43, R²=0.07, p>0.05; Adults, y=7.44x+74.23, R²=0.03, p>0.05). Mean latencies (across stimulus demands) were significantly lower for adults than children (Adults: 287.5±108.3, children (young and old): 324.6± 64.37, Welch’s unpaired t-test, p=0.007).

Conclusions:: Age related changes in peak velocity likely reflect age dependent properties of the crystalline lens while differences in the response latencies may reflect age related differences in higher order processing.(1). Kasthurirangan and Glasser. Vis Res (2006):46: 1507-1519.

Keywords: refraction • visual development