LENS-INDUCED ANISO-ACCOMMODATION

Despite the evidence for consensual accommodation in response to conse nsual accommodative stimuli, only a few studies have investigated the binocular accommodative response to unequal (aniso) accommodative stim uli. Past studies investigating an unequal binocular accommodative res ponse (aniso-accommodation) to anise-accommodative stimuli have been l imited by viewing conditions and measurement technique making the resu lts, which were equivocal, difficult to interpret. This investigation addressed these limitations by the following design parameters: (1) mo nocular dichoptic blur cues were provided in the binocular stimulus ta rget to provide subjects feedback on their anise-accommodative respons e and to alert the investigator of a monocular blur suppression respon se; (2) a training period was provided; (3) in the subjective method, each eye's stigma was positioned near the dichoptic letter viewed by t he other eye. By this method, a true anise-accommodative response coul d be differentiated from successive consensual responses; (4) a large range of anise-accommodative stimuli was used, 0.50-3.0 D, presented i n incremental steps of 0.5 D, allowing measurement of an average 0.75 D anise-accommodative response for the highest (3.0 D) anise-accommoda tive stimulus; (5) anise-accommodation was measured as a function of v iewing distance. For four of seven subjects, the gain of the anise-acc ommodative response was significantly greater at near than at far view ing distances; (6) anise-accommodation was confirmed objectively with measures of the response to steady state and step anise-accommodative stimuli, using a binocular SRI Dual Purkinje Eye Tracker Optometer Sys tem. The anise-accommodative response to step stimuli showed a very lo ng latency period (about 11 s) and a response time of 4.5 s. A potenti al benefit of anise-accommodation would be to overcome small amounts o f uncorrected anisometropic refractive error. This would preserve fine stereo acuity which is impaired by unequal intraocular image contrast . Anise-accommodation also may provide an appropriate efferent feedbac k signal for each eye's unique refractive error which could be used to guide developmental isometropization (attainment of equal refractive error in the two eyes.) (C) 1998 Elsevier Science Ltd. All rights rese rved.