Effect of a near-vision task on the response AC/A of a myopic population.

The effect of a 14 minute near-vision task on the response accommodative convergence/accommodation (AC/A) ratio was investigated for three refractive groups (each comprising N = 17)--emmetropes, early-onset myopes (EOM), i.e. myopia onset prior to 15 years of age, and late-onset myopes (LOM), i.e. onset 15 years or later. AC/A ratios were derived from accommodative stimuli of 3.0, 3.9 and 4.6 D. Accommodation was measured using an objective infra-red autorefractor which allowed unrestricted viewing through a semi-silvered mirror and this permitted concomitant vergence changes to be assessed using a Maddox rod and tangent scale. EOMs exhibit a significantly higher response AC/A ratio than the two other refractive groups. The implications of these modifications in response AC/A are discussed with reference to current models of accommodation-vergence interaction.