Subjects
This study involved the consecutive patients (high-resolution group) who underwent wavefront guided LASIK using the iDESIGN REFRACTIVE STUDIO [12] at the Baptist Eye Institute, Kyoto, Japan between 2012 and 2015, and who were followed up for 6-months postoperative. The control group (early custom group) underwent custom LASIK at Baptist Eye Institute between 2002 and 2007, and in whom the correction amount and patient age were matched to the patients in the high-resolution group. Approval for this study was obtained from the Institutional Review Boards of Kyoto Prefectural University of Medicine and the Baptist Eye Institute, Kyoto, Japan, and prior to enrollment, written informed consent was obtained from all patients in accordance with the tenets set forth in the Declaration of Helsinki.
Indication
Indication criteria for LASIK were as follows, the preoperative corneal topography deemed normal, corrected distance VA (CDVA) better than decimal 0.5, and the residual corneal bed more than 250 μm in depth. As it was required for the preoperative examination, all patients were strictly instructed to discontinue hard contact lens use for 3 weeks prior to surgery, and soft contact lens use for 2 weeks prior to surgery. Wavefront-sensor examination was performed 3 times for natural pupils and 3 times for dilated pupils. Among the wavefront data of the natural pupils, the one with the least excessive accommodation was selected and used as a data source for the corneal ablation profile. If there was excessive accommodation, the measurement was once-again performed on the day of the operation, and the measurement with the smallest difference from the subjective refraction was used for the surgery.
Surgical Procedure
In the high-resolution group, all wavefront-guided LASIK surgeries were performed using the iDESIGN REFRACTIVE STUDIO and iFS ADVANCED FEMTOSECOND LASER (Johnson & Johnson). When the corneal thickness was ≥550 μm, the flap formed was 130 μm, and when the corneal thickness was <550 μm, the flap formed was 120 μm. In the early custom group, LASIK was performed using the EC-5000 (NIDEK Co., Ltd., Gamagori, Japan) excimer-laser system (optimized aspheric transition zone ablation) [16], the VISX STAR S4 (Abbott Medical Optics, Santa Ana, CA) excimer-laser system (wavefront-guided ablation), [17] and the TECHNOLAS 217z (Bausch & Lomb, Rochester, NY) excimer-laser system (wavefront-guided ablation) [11] in 15, 8, and 28 eyes, respectively. A mechanical microkeratome was used in the LASIK procedure for flap creation (Table 1).
Pre and Postoperative care
Three days prior to surgery, all patients recieved 0.5% cefmenoxime hydrochloride eye drops (BESTRON; Senju Pharmaceutical Co. Ltd., Osaka, Japan) 4 times per day and 100mg of oral cefcapene pivoxil hydrochloride hydrate (FLOMOX; Shionogi & Co., Ltd., Osaka, Japan) 3 times per day. LASIK was performed under topical anesthesia. For the first postoperative week, all patients initially received 0.1% fluorometholone eye drops (FLUMETHOLON Ophthalmic Suspension 0.1; Santen Pharmaceutical) and 0.3% gatifloxacin hydrate eye drops (GATIFLO Ophthalmic Solution; Senju Pharmaceutical) 4 times per day.
Ophthalmic examinations
Prior to surgery and for 6-months postoperatively, spherical equivalent refractive error (SER) using Landolt C charts, uncorrected distance Visual Acuity (UDVA), CDVA, contrast sensitivity (CS) at 3, 6, 12, and 18 cycles per degree (cpd) using a CS testing instrument (CSV-1000; VectorVision, Greenville, OH), and HOA in a 4-mm and 6-mm area of the dilated pupil (0.5% tropicamide, phenylephrine hydrochloride) using an optical diagnostic instrument (OPD-Scan; NIDEK Co., Ltd.)18 were examined in each operated eye. All examinations were performed using the same equipment.
CS and Visual Acuity (VA) were subjected to a logarithmic transformation and analyzed as a continuous variate with log CS and logMAR. The predictability was calculated from the difference between the target and the refractive error measured 6 months post LASIK. The obtained wavefront data was fitted to a six-order Zernike polynomial, total HOA, coma-like aberration (third order + fifth order), and spherical-like aberration (fourth order + sixth order), with the spherical aberration then being calculated. Changes in the CS and HOA values were calculated by subtracting the preoperative values from the postoperative.
Statistical Analyses
The mixed-effect model was used to analyze study variables and changes (i.e., CS at 3 cpd, 6 cpd, 12 cpd, 18 cpd, and in 4mm and 6mm total HOA, Coma-like aberration, spherical-like aberration, spherical aberration) prior to surgery and at 6 months postoperatively with the preoperative and postoperative changes in both eyes as the objective variables, an identification (ID) number as the random effect, and each group as a fixed effect. The proportion was tested by the Fisher's direct test. The confidence level of the confidence interval was 95%, and a P-value of <0.05 was considered statistically significant. Linear regression analysis was used to clarify the relationship between the HOA change and the CS changes. Statistical analysis was performed with JMP PRO VERSION 14 STATISTIC SOFTWARE FOR WINDOWS (SAS Institute Inc., Cary, NC).