Esophoria patients having a low AC/A ratio will have less esophoria at near than at distance. This combination causes the problem to be improved at near and, additionally, added lens power will not greatly change the near phoria because of the low AC/A ratio (that is, each diopter of lens power will result in a unit change in accommodation that is associated with only a small amount of accommodative vergence).
After correcting the refractive error to improve sensory and motor fusion one needs to consider, not added lens power, but vertical prisms (that neutralize any vertical deviation present with the eyes in the fused position) for further improvement of sensory and motor fusion.
Prisms prescribed to neutralize even small amounts of vertical phoria can overcome symptoms and enhance horizontal fusion. Whether to consider prescribing lateral prisms at this point depends on the distance esophoria. For the rarely seen patient with esophoria at distance and a low AC/A ratio, base-out prisms are characteristically helpful at distance but may be overcorrecting at near --- requiring two pairs of glasses or specialty prism segments. Measures of the associated phoria (prism power that reduces fixation disparity to zero) usually indicate that nearly the full amount of any (disassociated) vertical phoria or esophoria needs to be corrected with prism.
Any amblyopia should be treated with passive occlusion and/or active training, primarily under binocular conditions. Suppression, which is usually slight and confined to the central retina, must also be treated whether or not amblyopia is present. The ultimate goal here is to eliminate any amblyopia and suppression so that sensory and motor fusion training can be maximally effective; however, sensory and motor fusion training can be introduced as the amblyopia and suppression are being eliminated.
Indeed, fusional training can be additionally effective in breaking down suppression and amblyopia. As is the case for all phoria patients, both of the vergence functions and accommodative facility need to be trained. Even though accommodative facility is readily achieved for both esophores and exophores, overall clinical success through training is more often achieved for exophores than esophores because convergence is more readily improved than is divergence.
Surgery is rarely recommended for distance esophoria patients having a low AC/A. The reason is that optical and training procedures are so often successful long-term, and further that surgical procedures frequently result in overcorrection with ensuing diplopia for several weeks or even months (von Noorden, 1985, p. 400).