Laser in situ keratomileusis nomogram development.

BACKGROUND: There is no standard laser in situ keratomileusis (LASIK) nomogram for the Nidek EC-5000 excimer laser when used with current software versions 2.23 or 2.25. Nomogram tables developed by various EC-5000 users differ significantly from one another. METHODS: We analyzed the results of our first 138 eyes treated for myopia and myopic astigmatism with the Nidek EC-5000 excimer laser, model 2b, long working distance. In addition to analyzing standard clinical outcomes, the correction values entered into the laser were compared to the achieved change in refraction for these eyes. A global nomogram parameter was created, incorporating the effect of optical zone size and patient age. After observing initial overcorrections, we elected to treat most of the eyes using a 20% reduction of the attempted spherical correction. RESULTS: The mean value for the attempted change in spherical equivalent refraction was -6.85 D. This correction was achieved with a standard deviation of -0.04 D at 1 month, -0.08 D at 3 months, and -0.09 D at 6 months after LASIK. The postoperative values for the uncorrected and spectacle-corrected visual acuity were similar to other published studies. However, scatterplots comparing the laser settings to achieved postoperative refractions showed a clear 20% trend toward overcorrection. This trend increased with patient age and optical zone diameter. CONCLUSIONS: The basic calibration values (factory standard) for software versions 2.23 and 2.25 are too aggressive for LASIK treatments. When using optical zone diameters of 6 mm and above, the spherical refraction values entered into the laser must be reduced by at least 20%. LASIK nomograms for the Nidek EC-5000 excimer laser should be specific for optical zone diameter and patient age.

Laser in situ keratomileusis for hyperopia.

PURPOSE: To examine the initial results of laser in situ keratomileusis (LASIK) for hyperopia. SETTING: Arzt für Augenheilkunde, Mannheim, and Photoingenieur, Wendelstein, Germany. METHODS: This retrospective study evaluated 43 eyes having hyperopic LASIK using the Automatic Corneal Shaper (Chiron Vision) and the MEL 60 excimer laser (model 94, Aesculap-Meditec). Patients were divided into two groups. Group 1 consisted of 20 eyes with a refraction from +1.00 to +4.00 diopters (D) and Group 2, 23 eyes from +4.25 to +8.00 D. Objective refraction and visual acuity were measured over 12 months. RESULTS: One year after LASIK, Group 1 had a mean spherical equivalent of +0.33 D (range -0.79 to +1.45 D) and Group 2, +1.91 D (range -0.08 to +3.71 D). Best corrected visual acuity remained unchanged in 35.0% in Group 1 and 56.5% in Group 2. Five percent in Group 1 and 7.3% in Group 2 lost more than 2 lines of best corrected visual acuity. CONCLUSIONS: Laser in situ keratomileusis for hyperopia resulted in less regression, minimal haze, and better predictability and stability than surface photorefractive keratectomy. Preoperative corneal radius appeared to be an important factor in eyes with high hyperopia.

Photorefractive keratectomy to treat low, medium, and high myopia: a multicenter study.

This prospective, multicenter study investigated what influence patient age, sex, and time to re-epithelialization after myopic photorefractive keratectomy (PRK) have on stability of achieved correction and intensity of corneal haze. Seven surgeons performed PRK to correct myopia on 325 eyes using the same operative procedure, type of laser, and post-PRK treatment. Follow-up was from six to 12 months. Results indicate that corneal haze intensity is influenced by the time to re-epithelialization of the treated corneal surface. Patient age and sex may also affect haze intensity, although the results from this study were not conclusive.