Patients having a distance exophoria and a high AC/A ratio will have less exo at near than at distance. For these exophores, their problems are usually worse at distance. Although added lenses are especially effective in changing vergence because of the high AC/A ratio, vision therapy is generally superior in eliminating the symptoms and is the initial therapy of choice after any indicated vertical prism correction has been prescribed.
The high AC/A ratio dictates prompt attention to the benefits of added lenses --- which is different for patients with low or normal AC/A ratios. Thus, immediately after assessing the refractive error and how corrective lenses facilitate sensory and motor fusion, consideration should be given to prescribing added minus power for the distance exophoria; and, perhaps, a plus addition for any eso at near. The calculated AC/A ratio gives a good indication of the actual vergence change that will take place.
Prisms are considered next, especially for any vertical deviation indicated on the associated phoria test. Prisms prescribed to neutralize even small amounts of vertical phoria can overcome symptoms and enhance horizontal fusion. 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 needs to be corrected with prism. In general, lateral prism correction should be deferred until after the effects of vision therapy have been determined.
These points about added lenses and prisms notwithstanding, it is necessary to recognize that in the management of high AC/A patients large distance exophorias usually require vision training in addition to any optics. After considering the various optical options for managing these high AC/A patients, their further management like that for all phoria patients and utilize treatment of amblyopia and suppression as well as training fusion and accommodation.
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.
For patients with distance exophorias and high AC/A ratios, vision training of fusional vergence is typically quite effective and is the initial treatment of choice. Additionally, fusional training can also be effective in breaking down suppression and amblyopia. As is the case for all phoria patients, both of the vergence functions (base-in and base-out) as well as accommodative facility needs to be trained. Even though vergence and accommodative facility is readily achieved for both esophores and exophores, overall clinical success through training alone is more often achieved for exophores because convergence is more easily improved than is divergence.
Surgery is not often advised for high AC/A phoria patients because of the problem of an ensuing postsurgical diplopia at one distance or the other. It is rarely undertaken because optical and training methods are so successful for these patients. On the rare occasion when they fail, controlled surgery with prompt followup for possible optics and training can be considered.