الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Laser in situ keratomileusis (LASIK) is one of the most popular techniques for the correction of refractive errors that has increased rapidly because of its effectiveness in correcting myopia with relatively few serious complications. Despite the overall success of LASIK, potential vision-threatening complications remain.
One of these, iatrogenic Keratectasia, is considered an important issue in the field of refractive surgery. Some mild degrees of post-LASIK keratectasia may be better detected at the level of posterior corneal surface. The posterior corneal shape is mainly used for early recognition of this pathologic condition. Thus, it is prudent to be able to accurately evaluate any changes in the posterior cornea after LASIK.
The Pentacam HR (Oculus, Germany) is a relatively new instrument that images the anterior and posterior corneal surfaces employing a rotating Scheimpflug camera. Measurements of corneal thickness and posterior elevation with the Pentacam rotating Scheimpflug camera have been reported to be highly reproducible and repeatable
In this study, 50 right eyes of 50 cases which have had uneventful LASIK correction for myopia and myopia with astigmatism were included, 10 cases were males and 40 cases were females, their age ranged from 18 to 36 years. All surgeries were performed by one surgeon, using the same excimer laser system, ablation profile and same intended flap thickness. Preoperative manifest refraction spherical equivalent ranged from -9 to -1 diopters. The patients were examined by Scheimpflug camera ( Pentacam HR) preoperatively and at one, three, six and twelve months postoperatively.
This study was conducted aiming for evaluating the posterior corneal changes after myopic LASIK correction, as well as trying to identify preoperative factors that may be correlated to the posterior corneal forward shift after LASIK which has been agreed to be one of the earliest signs of post–LASIK ectasia, using the Sheimpflug imaging system (Pentacam HR).
Several parameters were extracted and statistically analyzed:
1. The corneal thickness at the thinnest point.(CTmin)
2. Anterior corneal mean radii of curvature.(RmA)
3. Posterior corneal mean radii of curvature.(RmP)
4. Anterior corneal surface elevation off the best fit sphere at the thinnest point.(AET)
5. Posterior corneal surface elevations off the best fit sphere at the thinnest point.(PET)
6. The mean Q-value of the anterior corneal surface in the central 8 mm zone. (Q-Front)
7. The mean Q-value of the posterior corneal surface in the central 8 mm zone. (Q-Back)
8. The anterior chamber depth.(ACD