Actual Depth Ablation in LASIK and FEMTOLASIK Surgeries for Correction of Myopia and Myopic Astigmatism

Document Type : Original Article

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Department of Ophthalmology, Faculty of Medicine [For Girls], Al-Azhar University, Cairo, Egypt

Abstract

Background: Proper calculation of ablation depth associated with LASIK and FEMTOLASIK surgeries is mandatory to estimate the post-refractive surgery remaining stroma to avoid the possibility of post-operative ectasia and to correct the maximum error to meet the patient’s needs and safety.
Purpose: The current work aimed to assess the actual depths of ablation after the LASIK versus the FEMTO-LASIK surgeries.
Patients and Methods: Forty eyes of 20 patients were included in this prospective non-randomized interventional study. They had myopia or myopic astigmatism, and scheduled for LASIK or FEMTOLASIK surgery. Pentacam was used to check the thickness of the thinnest corneal location and to exclude the possibility of keratoconus. They were divided into two groups according to the technique used to correct the error. Group I for LASIK and Group II for FEMTOLASIK surgery. Ablation was performed in all cases using the Allegretto excimer laser machine. After surgery, all patients received a combination of topical tobramycin 0.3% and dexamethasone 0.1% eye drops four times daily for 10 days, and topical Sodium Hyaluronate eye drops [2 mg/ml] four times daily for one month. All patients were examined at one day and one week postoperatively for evidence of flap malposition, striae, epithelial defects, or diffuse lamellar keratitis. Pentacam was used for follow up at 3 months after surgery to re-evaluate the thinnest central location.
Results: In group I, the mean actual tissue ablation per one diopter was 13.3 microns for 6.5 mm treatment zone, and 11.9 microns for 6.0 mm treatment zone, while in group II, it was 13.4 microns for 6.5 treatment zone, and 11.8 microns for 6.0 treatment zone. There was insignificant difference between actual tissue ablation following the LASIK versus the FEMTOLASIK surgeries.
Conclusion: The actual ablation depth should be considered to calculate the remaining stromal depth after LASIK or FEMTOLASIK surgeries for treatment of myopia or myopic astigmatism to avoid the possibility of post- LASIK or FEMTOLASIK ectasia and to correct the maximum error that meets the patient’s needs.

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