الفهرس 
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Abstract
SUMMARY
Corneal laser refractive surgery reshapes the cornea based on the preoperative corneal curvature to reduce or eliminate refractive errors of the eye. Currently, LASIK is the most successful surgical treatment for the refractive error. The advantages are submicron precision of reduction of the ablation and minimal side effects .Standard ablation profiles for the correction of myopic astigmatism are based on the removal of tissue lenticules with sphero-cylindrical surfaces with the sequential delivery of laser pulses to remove the appropriate volume of corneal tissue.
It is of significant interest that a surgeon can rely on the calculated laser ablation depth readout to maintain the highest level of safety for the individual patient and still keep the number of “borderline cases” at an acceptable level.
Pentacam and optical coherence tomography (AS-OCT) allow the measurement of corneal thickness. The principle of Scheimpflug imaging uses optical sectioning of the cornea with maximum depth of focus, whereas OCT uses low coherence interferometry to measure corneal thickness.
In this study we compared between scheimpflug imaging system and anterior segment optical coherence tomography in measuring intended versus achieved ablation depth in laser in situ keratomileusis for myopia and myopic astgimatism.
Forty LASIK candidates were included in this study, the study included patients seeking LASIK aged 18 years old or more and younger than fifty, complaining of myopia and myopic astigmatism. All patients had normal corneal topography.
Exclusion criteria included patients below 18 years old, those with thin abnormal cornea, other ocular diseases or history of previous refractive surgery.
Preoperative preparation started with full history taking, and then every candidate was subjected to full ophthalmic examination, UCVA and BCVA measurement, K reading measurement, CCT measured by pentacam and AS-OCT.
Intended ablation depth calculated by wavelight EX500 software was recorded to be compared with clinically observed ablation depth calculated by Pentacam & AS-OCT 3rd month post-operative.
Corneal flap was created using Moria® M2 90,130-μm single use head according to thickness. Laser ablation was performed in the three groups using WaveLight® EX500 excimer laser system.
Postoperatively, all patients received standard treatment of antibiotic- steroid combination eye-drops in addition to artificial tears. In the first day postoperatively, all patients were subjected to UCVA measurement. Later on, UCVA was checked at first week, first month and third month follow up visits.
Clinically observed ablation depth was the main target to be evaluated in this study; CCT and ablation depth were measured using OPTOVUE® AS-OCT & ALLEGRO OCULYZER Pentacam at third month postoperatively.
Collected data were subjected to statistical analysis and the following results were obtained:
1. Better visual acuity results were obtained at 3rd month follow up visits than preoperative.
2. There was no statistical significant difference between intended ablation depth and clinically observed ablation depth 3rd month post-operative that means WaveLight EX500 excimer laser (Alcon) is predictable and accurate in treatment of myopia and myopic astigmatism.
3. Ablation depth readout calculated by the WaveLight EX500 excimer laser (Alcon) computer software when planning corneal refractive surgery is reliable.
4. Although both pentacam and AS-OCT are accurate, sensitive and specific in measuring the CCT and calculation of ablation depth Pentacam show slightly higher accuracy, sensitivity and same specificity as AS-OCT.