Muscular asthenopia and eccentric ablation after photorefractive keratectomy

PURPOSE: To investigate the relationship between muscular asthenopia and ec centric ablation after photorefractive keratectomy (PRK). METHODS: Sixteen eyes of eight myopic patients whose muscular asthenopia wa s corrected by subjectively accepted spectacle prism after PRK, with visual acuity better than 0.8, were followed for 6 to 14 months. On the basis of preoperative and postoperative data and corneal topography, we calculated t he total corrected corneal power using the Holladay formula and then measur ed the ablation eccentricity (h, millimeters) and its direction. According to the formula delta congruent to Dh, the prism effective value (delta) cau sed by the eccentric ablation was computed and compared with the objectivel y accepted spectacle prism. RESULTS: The subjectively accepted spectacle prisms were similar to calcula ted values from the formula. Mean difference was 0.10 +/- 0.25(Delta). The direction of the subjectively accepted prism was in the direction of the ab lation deviation. CONCLUSIONS: Eccentric ablation is an important cause of muscular visual as thenopia after PRK, The asthenopia may be corrected by spectacle prism, The spectacle prism value may be estimated by the formula delta congruent to D h.