This was a non-randomized controlled trail conducted in El-Hekma Eye-LASIK center, Menoufia governorate, Egypt. The study methods adhered to the tenets of the Declaration of Helsinki for use of human participants in biomedical research and were approved by ethical committee of Menoufia medical college. The assignment of patients was done according to the expected ablation depth and estimated residual stromal bed thickness with allocation ratio 2:1 in aberration free and corneal WFG groups respectively.
Enrollment in the study was restricted to those 21 years or older with stable refraction for more than 1 year, off soft contact lens for minimum 14 days prior to preoperative examination, preoperative central corneal thickness at least 480 µm, estimated residual stromal bed thickness at least 350 µm and total corneal HOAs ≥0.35µ. None of the patients in this trial had history of using rigid lenses.
Exclusion included any patient with any of the followingocular diseases; severe dry eye, blepharitis, corneal disease, contact lens warpage, cataract, uveitis and posterior segment anomalies involving the macula or optic nerve or any of the following systemic conditions; diabetes mellitus, connective tissue disease, pregnancy or nursing. Also, any patient who had previous ocular surgery including keratorefractive surgery was excluded.
Preoperative assessment included uncorrected distance visual acuity (UDVA) andbest spectacle corrected distance visual acuity (CDVA) utilizing Landolt C chart expressed in 20/20 and decimal notations for statistical analysis, manifest refraction and cycloplegic refractions using Topcon auto-refractometer 5500 (Topcon Inc., Japan), corneal topography, thorough slit lamp examination, and intraocular pressure measurement using Goldmanapplanation tonometer done after manifest refraction, CDVA and corneal topography to avoid bias. Corneal topography was carried out utilizing corneal wavefront topographer Schwind Sirius (SCHWIND eye-tech-solutions, Kleinhostheim, Germany) which combines a rotating scheimpflug camera with a placido disc and involves integrated pupillometry. Corneal wavefront map of the anterior corneal surface was obtained from corneal wavefront topographerSchwind Sirius up to the 7th order of Zernike polynomial at 6 mm diameter and expressed as root mean square (RMS) values, measured in micrometer (µm) mainly total, coma, spherical and trefoil aberrations. These measures were repeated 6 months postoperatively.
In this study, a procedure was labeled successful if achieved the desired outcomes in terms of efficacy and safety.Efficacy index was defined as the ratio between the postoperative UDVA to the preoperative CDVA while safety index was defined asthe ratio between the postoperative CDVA and the preoperative CDVA. Efficacy index around 1 and safety index more than 1 were desired. Failure was considered when the above outcomes failed to be achieved along with persistence or development of any of the following complications at 6 month postoperative follow up; corneal haze, persistent epithelial defects, ectasia, sterile infiltrate, infectious keratitis, central toxic keratopathy and steroid induced complications.
Planning for surgery
Organized Refractive Keratectomy Custom Ablation Manager (ORK CAM) software (SCHWIND eye-tech-solutions, Kleinostheim, Germany) was used to plan corneal wavefront customized treatments and aberration free aspheric treatments. Aberration free aspheric treatment involved ablation with optimized aspheric profile centered on the pupil center and the software compensated for the peripheral loss of energy while corneal wavefront mode involved ablation with corneal topography centered on the corneal vertex. Emmetropia was targeted in all patients.The entire manifest refraction was entered.
All patients underwent TransPRK using excimer laser system (SCHWIND AMARIS®500E, SCHWIND eye-tech-solutions, Kleinhostheim, Germany), with 500 Hz repetition rate for faster treatments and scanning spots and with smart pulse technology. Eye-tracking during laser ablation was achieved using a 1050 Hz infrared eye tracker centered on the pupil. Static cyclotorsion control (SCC) compensation was obtained for all patients in corneal WFG group and patients with astigmatism more than 1 D in aberration free group. Dynamic cyclotorsion control was implemented automatically for all treatment types. The optical zone was chosen by the surgeon. It ranged from 6mm to 7 mm in aberration free group and 6.5mm to 6.8 mm in corneal WFG group. The transitional zone was determined by ORKCAM software.The zone size for epithelial laser scrape was 8 mm.
After the patient being prepped, topical Benoxinate hydrochloride (BENOX®0.4%, Sterile Ophthalmic Solution, Eipico, Egypt) anesthetic drops were placed in the eye. Lid speculum was placed in the operative eye and a patch was placed over the fellow eye to avoid cross-fixation. The amount of desired correction, accounting for the vertex distance, was entered into the laser and the patient was asked to fixate on the laser centration light, then the excimer laser was used to remove the epithelium estimating that the central epithelial thickness of a normal cornea is 55µ at the center and 65µ at 4mm from the center, then continued to ablate the corneal stroma in non-touch technique. Topical Mitomycin-C (Mitomycin-C, kyowa Inc., Japan) 0.2 mg/ml was employed in all cases according to diopteric correction, with minimum 20 sec and maximum 60 sec at the end of the laser exposure followed by generous irrigation of the eye with room temperature balanced salt solution (20 seconds was used for corrections less than 3 diopters and 60 seconds for more than 3 diopters). After the surgery, a bandage contact lens was applied.
Postoperative treatment included a broad spectrum antibiotics eye drops,Moxifloxacin 0.5% (Vigamox, sterile ophthalmic solution, Alcon, USA) and lubricants eye drops,Hyaluronic acid (Hyfresh, JamjoomInc, KSA). Topical steroid drops, Prednisolone acetate 1% (PredForte, ophthalmic suspension, Allergan, Inc., Irvine, CA, USA), were added on the 2nd day postoperative starting with high frequency for one week, and then tapered gradually over two weeks. The bandage soft contact lens was removed 3-5 days postoperative.
IBM SPSS for Windows (Version 22.0, Armonk, NY: IBM Corp) was used. Categorical data was expressed as number and percentage, while numerical variables were expressed as mean ± SD. Normality of data variables were checked. For normally distributed data, preoperative and postoperative values were compared using paired t-test, while student t-test was used to compare the means between both study groups. Corresponding non-parametric tests (Wilcoxon rank test and Mann-Whitney test) were used if data didn’t follow a normal distribution. Correlation analysis was conducted between intended and achieved outcomes of interest. For all tests, p value of 0.05 or less was considered statistically significant.