Ocular Component Correlates of Tonic Accommodation

Abstract

Tonic accommodation (TA) and its adaptation have attracted considerable interest in recent years as putative risk factors for myopia (Ebenholtz, 1983) and TA is currently under investigation in prospective studies of adults (McBrien and Adams, 1989). TA has been widely studied as a function of refractive error. Maddock et al. (1981) found that emmetropes had significantly higher TA values than high myopes. McBrien and Millodot (1987) extended the classification of refractive error in their analysis, differentiating between late and early onset myopes. They found that while early onset myopes and emmetropes did not differ in TA, hyperopes had significantly higher and late onset myopes significantly lower levels of TA. Rosner and Rosner (1989) have demonstrated that the relationship between TA and refractive error in children is similar to that found in adults, with hyperopes having the highest levels of TA, followed by emmetropes, and myopes the lowest values. Correlation coefficients (r) between refractive error and TA have ranged from 0.61 (data on night myopia and refractive error from Irving (1957), 0.48 (Maddock et al., 1981), to 0.24 (McBrien and Millodot, 1987). Regression was not performed on the data from children in Rosner and Rosner (1989).