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First Author: I.Remesnikov KAZAKHSTAN
Co Author(s): V. Kim
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The use of femtosecond (FS) laser gets more clinical distribution in keratorefractive surgery because of the opportunity to create ultrathin corneal flaps with 90-100 ṁm thickness. In cases of high myopia and/or thin cornea Sub-Bowmens Keratomileusis (SBK) treatment can be performed as FS-LASIK-SBK. The purpose of the study is to examine visual acuity outcomes and accordance between the intended preoperative and resultant postoperative values of central corneal thickness (CCT) after FS-LASIK-SBK.
Astana Vision, Astana, Kazakhstan.
The retrospective study of the consecutive 42 bilateral myopic FS-LASIK-SBK treatments with the 3 month follow-up period was made. The group consisted of 21 patients: 8 males and 13 females, mean age 27.8 years (range 19 to 42 years). Excimer laser system Allegretto Wave Eye-Q 400 Hz and FS laser Allegretto FS-200 (Alcon) were used. Pachymetry measurements before and after treatment were made with rotating Scheimpflug camera Allegro Oculyzer (Pentacam II (Oculus), as well as with anterior segment optical coherent tomography (AS-OCT) Cirrus HD-OCT 400 (Zeiss) after treatment. The average value for the manifest refractive spherical equivalent (MRSE) was -6.79 ±2.00 D, (-1.25 to -11.5 D); mean values of refraction on cycloplegic exam with auto kerato-refractometer KR-8900 (Topcon) was: sphere: -6.46 ±2.14 D, (-0.50 to -10.50 D); cylinder: -1.84 ±1.93 D (0.00 to -7.75 D) before treatment. The average best-corrected distance visual acuity (BCDVA) before treatment was 0.145 logMAR, 71.4% eyes had visual acuity 0.1 logMAR and above, 16.7% had visual acuity 0.3 logMAR and below. Average preoperative pachymetry was 523.9 ±3.63 ṁm (476 to 575 ṁm).
In all cases after treatment we achieved emmetropia (MRSE = 0.00 D), with mean uncorrected distance visual acuity (UCDVA) 0.0595 logMAR. 92.9% eyes had visual acuity 0.1 logMAR and above and 4.8% had visual acuity 0.3 logMAR and below. Only in 1 case we note 1 line lost of UCDVA/BCDVA relatively to preoperative 0.00 logMAR BCDVA. Wilcoxon signed-rank test shows that the difference of preoperative BCDVA and postoperative UCDVA is within the significant value. The preoperative intended mean value of CCT was 414.98 ±24.73 ṁm (358 to 471 ṁm) and postoperative resulting mean CCT with Oculyzer was 401.91 ±27.76 ṁm (345 to 461 ṁm), with a mean difference -13.07 ±2.49 ṁm (-34 to +10 ṁm); postoperative resulting mean CCT with AS-OCT was 405.83 ±26.33 ṁm (352 to 460 ṁm), with a mean difference -10.19 ±6.26 ṁm (-31 to +11 ṁm). Wilcoxon test shows that the difference between the pre- and postoperative CCT is in the area of significance for the both methods. Spearman"s rank correlation analysis shows the correlation is in the area of significance between the ablation depth and CCT difference measured with Oculyzer and not reach it for AS-OCT difference.
High visual acuity outcomes of FS-LASIK-SBK method in the correction of myopia, also with the presence of a significant astigmatic component were received. The resulting lower level of CCT after treatment should be taken into account while planning the FS-LASIK-SBK procedures, exactly in cases with high ablation volume.