Ioannis G. Pallikaris

BACKGROUND: The purpose of this research was to study the visual outcome of excimer laser photorefractive keratectomy and laser in situ keratomileusis (LASIK) for the correction of moderate and high myopia. METHODS: Twenty partially-sighted eyes of 20 patients were divided into two groups, LASIK and photorefractive keratectomy. Ten eyes underwent LASIK and the other 10 photorefractive keratectomy. Follow up was at 1, 3, 6, and 12 months. The LASIK technique included a nasally based, 150 microns thick, 8.0 x 9.0 mm diameter, truncated, disc-shaped corneal flap created with a microkeratome; and the ablation of the stroma with a 193-nanometer ArF excimer laser. The flap was returned to its original position and held in place by apposition. The photorefractive keratectomy technique included mechanical removal of the epithelium and ablation of the stroma with a 193-nanometer ArF excimer laser. RESULTS: LASIK series: One eye had a ruptured globe during the second postoperative month and was excluded from the study. The preoperative spherical equivalent refraction ranged from -10.62 to -25.87 diopters (D). The attempted correction ranged from -8.00 to -16.00 D. Postoperative refraction and corneal topography stabilized between 4 and 12 weeks. Spectacle-corrected visual acuity was within 1 Snellen line of preoperative in all eyes. The refraction in six eyes (66.6%) was within +/- 1.00 D of the intended correction, and in eight eyes was within +/- 2.00 D (88.8%) at 12 months. The mean attempted correction (11.40 +/- 2.60 D) was close to the mean achieved correction at 12 months (11.96 +/- 3.10 D). The mean postoperative refractive astigmatism (1.50 +/- 0.97; range, 0.25 to 3.50 D) was close to the preoperative astigmatism (1.70 +/- 1.15; range, 0 to 3.75 D). Endothelial cell density at 12 months showed an average 8.67% of cell loss. All eyes showed a clear interface. Photorefractive keratectomy series: The preoperative spherical equivalent refraction ranged from -10.75 to -23.12 D. The attempted correction ranged from -8.80 to -17.60 D. Postoperative refraction showed regression throughout the follow-up period, and corneal topography did not stabilize. Spectacle-corrected visual acuity was within 1 Snellen line in eight eyes. Two eyes lost 2 and 3 Snellen lines. One eye was within +/- 1.00 D, and three eyes (30%) were within +/- 2.00 D of the intended correction at 12 months. The achieved correction mean (7.17 +/- 5.29 D) was 61% of the attempted mean (11.72 +/- 2.81 D) at 12 months. The postoperative refractive astigmatism (1.80 +/- 0.95; range, 0.50 to 4.00 D) was very close to the preoperative (1.90 +/- 1.33; range, 0 to 5.00 D). Endothelial cell density showed an average of 10.56% cell loss at 12 months. The mean haze at 12 months was 1.2 (0 to 4 scale). CONCLUSION: LASIK, although more complicated because of the use of a microkeratome, was more effective than photorefractive keratectomy in higher myopes. LASIK created less corneal haze. The refraction was more stable with LASIK in the correction of high myopia. Its predictability was three times that of PRK.

PURPOSE: To identify factors that can lead to corneal ectasia after laser in situ keratomileusis (LASIK). SETTING: University refractive surgery center. METHODS: In this retrospective study, the charts of all patients (2873 eyes) who had LASIK between May 1995 and November 1999 were reviewed. Fourteen patients (19 eyes, 0.66%) developed post-LASIK ectasia. The mean follow-up was 16.32 months (range 6 to 42 months). RESULTS: No patient with an attempted correction less than 8.00 diopters or a residual corneal bed thickness greater than 325 microm experienced post-LASIK ectasia. There was a statistically significant positive correlation between corneal residual bed thickness and increasing patient age. CONCLUSION: Despite the limitations of the small sample size, the study's results suggest that parameters besides residual corneal bed thickness (eg, age, attempted correction) may have to be considered to avoid post-LASIK ectasia.

PURPOSE: To measure the rigidity coefficient of a large number of subjects at clinically encountered intraocular pressures (IOPs) and to examine the possible correlation of ocular rigidity with other factors, such as the age of the patients, ocular parameters (axial length and corneal thickness), and pathologic conditions affecting the eye. METHODS: The pressure-volume relationship and the ocular rigidity coefficient (K) were determined in 79 eyes undergoing cataract surgery, by injecting 200 microL of saline solution (in steps of 4.5 microL) through the limbus into the anterior chamber, while continually monitoring the IOP with a transducer, up to the limit of 60 mm Hg. Data within an IOP range of 10 to 35 mm Hg were used to calculate the scleral rigidity coefficient. All measurements were taken at the same time of day, to eliminate any possible diurnal variation. RESULTS: The mean ocular rigidity coefficient was 0.0126 mm Hg/microL (95% confidence interval [CI], 0.0112-0.0149). A statistically significant positive correlation between the rigidity coefficient and age of the patient was found (P = 0.02), whereas similar findings were not observed for the examined ocular parameters (axial length, P = 0.09; and corneal thickness, P = 0.12). No correlation was found for patients with diabetes mellitus (P = 0.39), age-related macular degeneration (P = 0.55), and hypertension (P = 0.45). CONCLUSIONS: The present study provides quantitative data on the ocular rigidity coefficient based on measurements in a large series of living human eyes. A positive correlation between the ocular rigidity coefficient and the patient's age was documented.

Using a modified microkeratome, nasally based central corneal flaps were created on six human blind eyes at a depth of 300 microns. The flaps were allowed to heal with a bandage soft contact lens, using neither sutures nor bioadhesives. The optical quality of the corneas was evaluated with biomicroscopic examination, computer-assisted topography, and optical pachometry during a 3-month follow-up period. The maintenance of transparency and lack of distortion of the corneal surface 3 months after surgery support the concept that the flap technique may be useful in laser in situ keratomileusis.