The effect of surgery on the AC/A ratio.

The accommodative convergence/accommodation (AC/A) ratio is used clinically as a diagnostic tool in the assessment of convergence excess and near esotropia and the differentiation of true and simulated divergence excess. An abnormally high AC/A ratio has been implicated in the aetiology of some forms of strabismus but the evidence for alteration in the ratio following surgery is inconclusive. In a prospective study of 38 patients the effect of routine squint surgery was investigated in concomitant strabismus. The AC/A ratio was found to decrease significantly after surgery in both esotropes and exotropes. Furthermore a trend was demonstrated which suggested an increased risk of overcorrection in esotropes with a high (> or = 7:1) pre-operative AC/A ratio.