Comparison of Corneal Thickness Measurements Between Orbscan Topography System and Ultrasonic Pachymetry before and after LASIK

PURPOSE: To report the difference of the values of the corneal thickness measurement measured by Orbscan topography system and ultrasonic pachymetry is different between pre-LASIK and post-LASIK. METHODS: The corneal thickness measured by these two methods was compared in 32 pre-LASIK eyes of 18 subjects and 31 post-LASIK eyes of 20 subjects passed 3 months after laser in situ keratomileusis (LASIK). RESULTS: In the pre-LASIK eyes, the cornea measured thicker by Orbscan topography system than by ultrasonic pachymeter (16.94+/-13.1 microgram, average +/- standard deviation, p=0.001). In the post-LASIK eyes, there was no statistically significant difference in the values of corneal thickness measurement between two methods (-9.58+/-27.88 microgram, p=0.0653). CONCLUSION: We must give attention to the interpretation of values of corneal thickness measurement measured by Orbscan topography system and ultrasonic pachymetry because the correlations between the two methods in pre and post-LASIK eyes are different. We assume that differences of the values of measurement between the two methods may result from either technical errors of the measurers , interference of corneal interface, or change of tear film.

Factors Associated with the Posterior Corneal Surface Elevation in Mmyopic Eye

PURPOSE: To know the factors associated with the posterior corneal surface elevation in myopic eye. METHODS: The posterior corneal surface elevation (PCSE), keratometry, central corneal thickness (CCT), peripheral corneal thickness (PCT), thinnest corneal thickness (TCT) were measured in 64 right myopic eyes with the Orbscan topography system. The correlation between PCSE and age, refractive error, intraocular pressure (IOP), keratometry, CCT, TCT, PCT, PCT-CCT, PCT/CCT, PCT-TCT, and PCT/TCT was evaluated. RESULTS: The posterior corneal surface elevation has correlation with CCT (r:.0.3306, p:0.0071), TCT ( r :.0.4094, p:0.0007), PCT-CCT(r:0.3326, p:0.0068), PCT/CCT (r:0.3759, p:0.0020), PCT-TCT (r: 0.4750, p:0.0001), and PCT/TCT (r:0.5145, p:0.0001) but does not have correlation with age, keratometry, refractive error, IOP (r:.0.0627, p:0.6225), and PCT. CONCLUSIONS: In myopic eyes, the posterior corneal surface elevation correlates with central corneal thickness and specifically the ratio PCT to TCT.

Flap Complications of LASIK

Laser in situ keratomileusis[LASIK]for myopia reduces the risk of corneal haze but adds to the risk of flap complications. We assessed the incidence of flap complications overall, the management, the impact of the complications on best corrected visual acuity[BCVA], and the trend in these complications during the surgeon's learning curve in the series of 621 eyes undergoing LASIK.Twenty[3.2%]of 621 eyes had flap-related complications.The incidence of intraop-erative complications was fourteen eyes[2.2%], and it included irregular keratectomy in ten eyes[1.6%], incomplete keratectomy in four eyes[0.6%].The incidence of postoperative complications was six eyes[1.0%], and it included epithelial ingrowth in five eyes[0.8%], and diffuse lamellar keratitis in one eye[0.2%].There weren't grave complications such as infectious keratitis or corneal perforation.There was no change between preoperative and postoperative BCVA in seventeen eyes[85%].No eye lost 2 or more lines of BCVA because of flap complications. In conclusion, flap complications after LASIK were relatively uncommon, and rarely lead to a permanent decrease in visual acuity.Physician experience with the microkeratome and the careful handling of the corneal flap may be important to decrease the incidence of flap mplications.But even though it occurs, proper management and treatment will result in good surgical outcomes without grave visual impairment.