An inverse relationship between accommodative convergence to accommodation (AC/A ratio) and the monocular amplitude of accommodative response was found in ten young patients with accommodative esotropia. Drugs which act on the ciliary muscle caused reciprocal changes in these two measures: a cycloplegic increased the AC/A with a decrease in amplitude, while a miotic lowered the AC/A and raised the amplitude. The suggestion is made that the magnitude of the AC/A in these cases may be determined by the efficiency of the peripheral accommodative mechanism. A high AC/A ratio would indicate a weakness of this mechanism. Thus, greater effort would be necessary to bring about a unit change in accommodation and more accommodative convergence is produced.
Chin NB, Breinin GM. Ratio of Accommodative Convergence to Accommodation: Accommodative Strabismus. Arch Ophthalmol. 1967;77(6):752–756. doi:10.1001/archopht.1967.00980020754007
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