Optical Analysis of Visual Improvement after Correction of Anisometropic Amblyopia with a Phakic Intraocular Lens in Adult Patients

Abstract

To analyze possible reasons for an increase in visual acuity observed in myopic patients with anisometropic amblyopia after implantation of a phakic intraocular lens (PIOL) using a theoretical eye model. Retrospective case series. Fifty-nine eyes of 48 patients with anisometropic amblyopia implanted with an angle-supported PIOL. Inclusion criteria were anisometropia of at least 3 diopters (D) and a best spectacle-corrected visual acuity (BSCVA) of 0.7 or less in the best eye. Follow-up was performed at 1, 3, 6, and 12 months and then annually for up to 10 years. The theoretical analysis of mechanisms to explain the visual improvement was performed using a theoretical eye, based on the Kooijman model, in which the measured values of radii and thickness of the different surfaces were substituted. The magnification and spot size were calculated by a ray tracing process. Uncorrected visual acuity, improvement in best spectacle-corrected visual acuity, and spherical equivalent. Mean gain in visual acuity was 3 lines (range, 0-7 lines). Fifty-four eyes (91.5%) gained at least 1 line of visual acuity, whereas no eyes lost lines of vision. The change in BSCVA did not correlate with preoperative BSCVA (Pearson coefficient, r = 0.19) or with the degree of anisometropia (Pearson coefficient, r = 0.23). The calculations using a Kooijman eye model corrected with spectacles and with a PIOL accounted for the full increase in visual acuity in terms of the magnification (increased by a factor of 1.2) and the spot size (reduced by a factor of 2). After implantation of a PIOL, the visual acuity of myopic patients with anisometropic amblyopia showed a significant increase. This increase was explained using a theoretical eye model not only in terms of magnification but also including changes in aberrations. An evident role of neuroprocessing in this visual improvement was not identified.