Change in Fluorescein clearance and Tear Film Stability following Laser in situ Keratomileusis

PURPOSE: To study the change in corneal sensitivity, tear film stability, tear clearance and blink rate after LASIK. METHODS: The authors have performed LASIK to correct the visual acuity in myopia of 3 males and 18 females(42 eyes). The corneal sensitivity(Cochet-Bonnet esthesiometer), tear film break-up time, fluorescein clearance and blink rate were measured prior to operation, 2 weeks, 1 and 3 months after LASIK. RESULTS: There was decrease in corneal sensitivity after LASIK, which did not recover to the pre-operative level by 3 months after LASIK. To restore corneal sensitivity, more time was needed for regrowth and maturation of the nerve fiber. The decrease in BUT scores 1 and 3 months after LASIK was statistically significant. The decrease in blink rate after LASIK was also statistically significant. The increase in FCT concentration grade was not statistically significant. There was a trend toward a reduction in blink rate in the group with more correction. CONCLUSIONS: Symptoms suggestive of relative tear deficiency such as foreign-body sensation, visual fluctuation and absence of reflex tear have described after LASIK. Change in corneal sensitivity, tear film stability and blink rate were associated with such dry eye symptoms.

Multiple Logistic Regression Analysis of Factors in Refractive Outcome of Photorefractive Keratectomy(PRK)

PURPOSE: The purpose of our study was to evaluate the preoperative factors associated with refractive outcome of photorefractive keratectomy. METHODS: 113 eyes of 84 patients were observed for 1 year after PRK. We examined the outcome of PRK with efficacy, predictability, and stability and analyzed data through multiple logistic regression analysis to evaluate the independent association of multiple preoperative factors with each of three principle results. RESULTS: Lesser intended correction and lesser intraocular pressure were associated with an increased likelihood of achieving 20/25 or better uncorrected visual acuity. Greater intraocular pressure and lesser corneal opacity were associated with increased predictability. Lesser intended correction was associated with an increased likelihood of stability. Preoperative factors associated with postoperative uncorrected visual acuity are amount of intended correction and intraocular pressure. Predictability is associated with intraocular pressure and degree of corneal opacity. Stability is associated with greater amount of intended correction. CONCLUSIONS: If we consider these factors, we can expect more exact outcome in patient selection, determining timing of fellow eye surgery.

Differences in Keratocyte Apoptosis Between Laser and Mechanical Removal of Corneal Epithelium for PRK in Rabbits

PURPOSE: To evaluate the effects of different corneal epithelial manipulations in PRK procedure on keratocyte apoptosis. METHODS: Rabbit cornea was examined qualitatively and quantitatively after epithelial scraping(Group I), epithelial scraping followed by PRK(Group II) and transepithelial PRK(Group III). Each of them were compared with that of unwounded control. RESULTS: The number of anterior stromal keratocytes had decreased significantly and TUNEL-positive cells were significantly increased in the anterior stroma in group I and group II on POD 3 days compared with control group(p<0.05). There was a statistically significant increase in the number of anterior stromal keratocytes in group II compared with group III on POD 1 month(p<0.05). In group I and II, keratocytes that had morphologic changes consistent with apoptosis were detected with transmission and scanning electron microscopy on POD 3 days. But in group III, there were many normal appearing keratocyte in the anterior corneal stroma, and few keratocytes undergoing apoptosis. CONCLUSIONS: Transepithelial PRK induced lower levels of keratocyte apoptosis in rabbit cornea compared to those induced from epithelial scraping followed by PRK. This suggests that transepithelial PRK could be useful in preventing or minimizing refractive regression and corneal opacity, especially in cases of myopia or retreatment after regression.