Heterophoria and Fusional Reserves Changes after Photorefractive Keratectomy for Myopia

The goal of this study was to compare differences in the mean heterophoria and fusional amplitudes before and after photorefractive keratectomy (PRK) for myopia. In a prospective controlled study, myopic patients were treated with aspheric and wavefront-guided (personalized) PRK. The manifest refraction, visual acuity, fusional amplitudes and heterophoria were evaluated preoperatively and at three and six months postoperatively. Fusional amplitudes were measured at far (six meters) and near (40 centimeters) by rotary prism and heterophoria was evaluated at nearby Maddox wing. A total of 48 cases (96 eyes, 68.75% female) were treated, with a mean age of 26.70±4.89 years (18-34 years). In the fusional reserves, comparisons between preoperative and six months postoperative means showed that far and near convergence reserves (or base out recovery points) and near divergence (or base in recovery point) were decreased significantly (p-values were 0.013, 0.002 and 0.008, respectively). In heterophoria measurements, contrary to the rest of the deviations, exophoria was increased, but not significantly (p=0.063). Findings of this study imply that far and near convergence amplitude (or base out reserves) were decreased significantly after keratorefractive surgery. The other fusional reserves were similarly decreased at three months postoperatively and returned to the preoperative values at six months.