We reviewed the records of patients who underwent Q value guided refractive surgery (including LASIK and LASEK) at Shanghai Sixth People's Hospital during 2007 and who had a postoperative follow-up at year 3 after surgeries. Aspheric LASIK was performed on 34 eyes of 17 patients (8 eyes of 4 males, 26 eyes of 13 females), and aspheric LASEK was performed on 36 eyes of 18 patients (4 eyes of 2 males, 32 eyes of 16 females). The study protocol was approved by Ethics Committees of the hospitals and shanghai Jiaotong University. Written informed consent was obtained from each subject. Patient demographics are summarized (Table 1). All the patients in this study were given information about the surgical procedure and possible complications. Inclusion criteria were the patients without pathologic myopia or other eye disease and without related systemic diseases, such as diabetes mellitus, preoperative manifest refraction greater than -6.00 diopters (D) and astigmatism up to -2.50 (D). Exclusion criteria included patients whose uncorrected distance visual acuity (UDVA) was less than 20/20 (6/6) with suboptimal visual outcome, complications following surgery such as dry eye or haze. All surgeries were performed by one surgeon (J.Z), who had extensive experience with refractive surgery.
All patients underwent refractive surgeries using the ALLEGRETTO WAVE Eye-Q 400-Hz excimer laser ((Wave-Light AG, Erlangen, Germany) with the fine adjusted-customized ablation treatment (F-CAT) algorithm. The targeted Q value was set according to the mean of Q1 and Q2, which were calculated by the corneal eccentricity of two main meridians within 30 degrees. The preoperative K-value and Q-value determined by corneal topography were used for aspheric ablation.
Surgical procedure: In the LASIK procedure, a corneal flap (thickness of approximately 110–130 μm) was created using an auto mechanical microkeratome (Moria 90, France). In the LASEK procedure, the corneal epithelium was incised with a trephine placed centrally, and 20% alcohol was applied for 15#x2013;20 s and then detached an epithelial flap. After these procedures, laser ablation was performed to manifest the refraction.
All patients were examined before and at year 3 after the surgery. The evaluations included Q value changes of the anterior corneal surface, safety and efficacy of the operation, residual refractive errors, topography regularity indices (including index of surface variance [ISV], index of vertical asymmetry [IVA], index of height asymmetry [IHA]) and corneal higher order aberrations (spherical aberration and coma). Safety was evaluated in terms of a calculated safety index (= mean postoperative corrected visual acuity/mean preoperative corrected visual acuity). Efficacy was determined by calculating an efficacy index (= mean postoperative uncorrected visual acuity/mean preoperative uncorrected visual acuity).
Corneal topography was recorded using an Allegro topolyzer (Allegro topolyzer, Wavelight, Germany). The topographic maps of each eye were examined by one observer and three topographic maps were recorded for each eye. From the corneal topography, the wavefront errors of the anterior corneal surface at 6 mm pupils were calculated and decomposed into Zernike polynomials to the 7th order. Zn m is the Zernike coefficient of radial order n and angular frequency m. Spherical aberration was expressed as Z4 0 and coma was expressed as Z3 1.
All parameters were recorded as mean ± standard deviation. Student t-test was performed to determine statistically significant differences. The Pearson correlation and multiple linear regression was calculated to determine relevant factors analysis in stepwise method. A P value <0.05 was considered statistically significant. Statistics were calculated using SPSS Version 17.0 (IBM).
BMC Ophthalmol. 2012;12(15) © 2012 BioMed Central, Ltd.