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Abstract
Excimer laser refractive surgery is currently the most common surgical procedure performed on the central cornea. LASIK involves photoablation of corneal stroma deep to an anterior corneal flap. Flaps have traditionally been created with mechanical microkeratomes, but more recently, femtosecond laser technology has emerged as an alternative for flap creation.(149)
Femtosecond lasers are ultrafast lasers that precisely photodisrupt tissue by using very short duration energy pulses. The low amount of energy imparted to the tissue minimizes collateral tissue damage in theory.(184,185)
In our study, we aimed to evaluate the use of femtosecond laser in flap creation and its implication on the procedure outcomes, as well as to compare it with conventional LASIK. Outcome measures included flap dimensions, visual acuity changes, contrast sensitivity and wavefront changes, as well as device failure rate and related complications.
47 LASIK candidates were included in this study, divided randomly into two groups. The FS group included 30 eyes of 15 patients, and the Moria group included 32 eyes of 32 patients. The study included any patient seeking LASIK aging 18 years or more, complaining of myopia, hypermetropia with or without astigmatism. All patients had normal corneal topography with central corneal thickness 500μ or more. Younger individuals as well as those with thin cornea, other ocular diseases, or history of previous refractive surgery, were excluded from the study.
Preoperative preparation started with full history taking, then every candidate was subjected to full ophthalmic examination, UCVA and BSCVA measurement, K reading measurement, CCT measurement, as well as corneal topography. Also, contrast sensitivity and wavefront measurements were obtained.
Then, in the FS group, flap was created using VisuMax® 200 kHz femtosecond laser system, while in the Moria group, flap was created using Moria® M2 130μ disposable head. Laser ablation was performed in both groups using WaveLight® Allegretto excimer laser system using ablation zone of 6.5 mm.
Postoperatively, all patients received standard treatment of antibiotic – steroid combination eye-DROPs in addition to artificial tears. In the 1st day postoperatively, all patients were subjected to UCVA measurement and epithelial integrity check using sterile fluorescein strips. Later on, UCVA was checked at both 1st and 3rd month follow up visits, while contrast sensitivity and wavefront measurements were evaluated at both 3rd and 6th month follow up visits.
Flap dimensions were the main target to be evaluated in this study. Flap thickness was measured in both groups using US pachymetry intraoperatively, then using AS-OCT at 1 month postoperatively. Flap diameter and hinge length were measured intraoperatively using standard caliper.
Collected data were subjected to statistical analysis and the following results were obtained:
1. Significantly - better visual acuity results were obtained in the FS group at both 1st and 3rd month visits.
2. Significantly - higher than intended flap thickness was obtained in both groups, but to a significantly - lesser extent in the FS group.
3. Larger than intended flap diameter was obtained in the FS group only.
4. Significantly - higher than intended flap hinge length was obtained in both groups, but to a significantly - lesser extent in the FS group.
5. Significantly - higher contrast sensitivity at all spatial frequencies was obtained in the FS group at both 3rd and 6th month.
6. RMS of coma increased only at 6th month in the FS group. No significant difference between both groups at any time point was achieved.
7. Regarding RMS of trefoil, no significant change was found in the FS group, while a non – significant decrease in the Moria group was found.
8. Regarding RMS of spherical aberrations, no significant change in the FS group, while a significant increase at 3rd and 6th months was found in the Moria group. No significant difference between both groups was found.
9. RMS of 2ry astigmatism significantly increased at 3rd month in the FS group, and in the Moria group at both 3rd and 6th month were found. Higher induced 2ry astigmatism in the FS group was found at 3rd month only.
Regarding other published literature, results of this thesis were found comparable in all aspects except for some different outcomes in the wavefront measures. These outcomes are thought to be probably due to small sample size in this thesis.