Effects of Orthoptic Treatment on the CA/C and AC/A Ratios in Convergence Insufficiency

PURPOSE: To evaluate the effect of orthoptic treatment on the AC/A (A, accommodation; C, convergence) and CA/C ratios in subjects with convergence insufficiency (CI). METHODS: The change in AC/A and CA/C ratios after a 12-week period of home-based orthoptic treatment was examined in 10 subjects (mean age, 25.4+/-4.1 years [SD]). Both the AC/A and CA/C ratios were measured by using gradient response methods. For the AC/A ratio, the gradient phoria method was used, and for the CA/C ratio the prism-induced change in accommodation was measured with a refractometer. RESULTS: No change in the AC/A and CA/C ratios (P>0.05) were found after orthoptic treatment. However, improvements were found (P<0.05) in the fast and slow vergence mechanisms. CONCLUSIONS: Despite improvements in the fast and slow vergence mechanisms no change was found in the AC/A and CA/C ratios after orthoptic treatment in CI subjects. This finding is unexpected in light of the present understanding of CI, and an alternative theory is proposed.