Assessment of the CA/C ratio in a myopic population.

The convergent accommodation/convergence (CA/C) ratio was measured in 30 subjects comprising 10 late-onset myopes (LOM's), i.e., myopia onset at 15 years of age or later, 10 early-onset myopes (EOM's), and 10 emmetropes. The accommodation loop was opened by two methods: (1) the subject viewed a 0.1-mm diameter spotlight at distances of 33 and 100 cm and (2) the subject viewed near-type (viewing distance 33 cm) through 0.5-mm pinholes. Convergence was stimulated by the introduction of 3 and 6 delta base-out prisms before the right eye and the accommodative response of the left eye was measured using an objective infrared optometer (Canon Autoref R-1). There was no significant difference in CA/C between the three refractive groups with either method. The implications of this finding are discussed with reference to previous work on accommodative convergence/accommodation (AC/A) and disparity-induced accommodation and in relation to accommodation-vergence synkinesis in late-onset myopia.