The rate of change of accommodative convergence with accommodation (AC/A ratio) is of considerable practical, as well as theoretical, importance. It is the purpose of this study to report the effect of incomplete cycloplegia induced by systemic medication.
The complex mechanism of convergence consists of 4 components: tonic, proximal, fusional, and accommodative convergence. Experimentally, by eliminating change in tonic, fusional, and proximal convergence, one may measure the change in convergence which results from accommodative stimulus. The AC/A ratio, or rate of change of accommodative convergence with accommodation, is computed by dividing the change in lateral phoria in prism diopters by the change in stimulus to accommodation in diopters.Two basic techniques have been used in the clinical measurement of the AC/A ratio: the variable distance method and the gradient method. In the variable distance method the changes in stimulus to accommodation are produced by changes in the
PEMBERTON JW, BROWN DJ. Accommodative ConvergenceA Study of the Effect on the AC/A Ratio of Partial Cycloplegia Induced by Systemic Medication (Orphenadrine Citrate). Arch Ophthalmol. 1962;68(3):348-352. doi:10.1001/archopht.1962.00960030352009