Corneal topographic changes after noncontact homiun : YAG laser thermal keratoplasty to correct hyperopia

Purpose : To analyze the changes in corneal curvature induced by laser thermal keratoplasty (LTK) to correct hyperopia. Setting : Cullen Eye Institute, Baylor College of Medicine, Houston, Texas. Methods : We performed LTK on nine hyperopic eyes using a noncontact holmium : YAG (Ho :YAG) laser. Five eyes received a single ring of eight spots at the 6 mm zone (Group A) ; four received a second ring of eight at the 7 mm zone (Group B). Computerized videokeratography (CVK) was obtained preoperatively and 1, 30, 90, 180, and 360 days postoperatively. We calculated the net dioptric changes in the following CVK values : corneal curvature at the 1, 3, 5, and 7 mm zones ; effective corneal refractive power (Eff RP) ; and spherical equivalent of subjective manifest refraction (SE SMR). We classified difference maps according to the pattern of induced change. Results : At 1 year, steepening at the 1, 3, 5, and 7 mm CVK zones was 0.5 diopter (D), 0.6 D, 0.1 D, and -0.42 D, respectively, in Group A and 1.5 D, 1.5 D, 1.1 D, and 0.54 D, respectively, in Group B. Effective corneal refractive power increased 0.6 D in Group A and 1.5 D in Group B. Mean change in SE SMR was -0.6 D in Group A and -1.4 D in Group B. Most regression occurred during the first 90 days. Difference maps showed five bow-tie, two irregularly irregular, one semicircular, and one homogeneous patterns. Conclusions : Noncontact Ho :YAG LTK produced peripheral corneal flattening and central corneal steepening. A greater change in curvature was produced using a two-ring treatment.