T Kohnen1, S E Husain, D D Koch. 1. Cullen Eye Institute, Department of Ophthalmology, Baylor College of Medicine, Houston, Texas 77030, USA.
Abstract
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 7mm 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.
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 7mm 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.