Response AC/A ratios are elevated in myopic children.

In children little is known about the relationship between the AC/A ratio and the development of myopia, although they have been linked in adults. The purpose of this study was to investigate the interaction between accommodation and convergence and its relationship to refractive errors in children. Accommodation was measured for the right eye using the Canon R-1 autorefractor, and concomitant changes in vergence were assessed using a Maddox rod and a Risley prism before the left eye. Thirty-three myopic and 68 emmetropic children were tested wearing best subjective correction while looking at a distant (4.0 m) letter array and a near (0.33 m) one through additional plus and minus lenses. Lens-induced and distance-induced response AC/A ratios were calculated from the data. Both types of AC/A ratios are elevated in myopic children, who show reduced accommodation and enhanced accommodative convergence. Myopic children with esophoria underaccommodate at near. This suggests that a child who is esophoric must relax accommodation to reduce accommodative convergence and maintain single binocular vision. The reduction in accommodation could produce blur during near work, which could induce myopia as in animal models.