Synkinesis of accommodation and vergence in late-onset myopia

The accommodative response (AR) to disparity-vergence and blur stimuli was determined for 45 subjects; 15 emmetropes, 15 late-onset myopes (LOM's), and 15 early-onset myopes (EOM's). The accommodative response was measured at approximately 1-s intervals for 50 s using an objective infrared optometer. Disparity-driven accommodation was induced by a 4 delta base-out prism at accommodative stimulus levels of 2.50 and 3.25 D. LOM's show significantly higher levels of disparity-induced accommodation when compared with the other two refractive groups. Blur-induced accommodation was produced by increasing the accommodative stimulus from 2.50 to 3.25 D with no concomitant change in vergence stimulus. EOM's exhibit less blur-induced accommodation compared with LOM's and emmetropes. These results are discussed with reference to differences in accommodation-vergence synkinesis between LOM's and EOM's, and in relation to the etiology of late-onset myopia.