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[GDx before and after LASIK in middle and high myopia].

AIM
To evaluate, if there are statistically significant changes in the RNFL (retinal nerve fibre layer) after LASIK. To evaluate, if the changes in the corneal structure caused by LASIK involve the results of the RNFL by means of GDx VCC.


MATERIAL AND METHODS
The group consisted of 100 eyes of 51 patients (32 women, 19 men); the mean age was 28.55 +/- 5.1 years (18-50 years). The average refractive error in spherical equivalent (SE) was -5.46 +/- 1.40 D (dioptres). The group was divided into two subgroups: subgroup A (69 eyes with SE from -3.25 D to -6.0 D), and subgroup B (31 eyes with SE from -6.25 D to -12 D). The patients underwent the LASIK procedure to correct the myopia. The thickness of the RFNL was measured by means of GDx analyzer with variable corneal compensator. The measurements were performed before and 1, 3, 6, and 12 months after the LASIK procedure. The results of the measurements were statistically evaluated by means of the Mann-Whitney U test.


RESULTS
The statistically significant difference in the RNFL thickness (p < 0.05) was found in "Superior Average" 3 and 12 months after LASIK (p = 0.016, p = 0.018), in "Inferior Average" in all controls (p = 0.047, p = 0.0001, p = 0.0003, p = 0.001) and in "NFI" after 12 months (p = 0.039). The values of difference in RNFL thickness in separate measurements after LASIK between both subgroups A and B were evaluated by means of Mann-Whitney U nonparametric test. Statistically significant difference in "Inferior Average" was found 1,6, and 12 months after LASIK (p = 0.01, p = 0.01, p = 0.04); in "TSNIT Average" after 6 months (p = 0.01); in "NFI" values after 1 month (p = 0.03). In "Superior Average, no statistically significant difference was found.


SUMMARY
In our group we have found statistically significant decrease of RNFL thickness after LASIK in every single quadrant. Clinically, the differences in RNFL thickness before and after LASIK were minimal. We suppose the measurements by means of GDX are influenced by changes in the polarization features of the cornea caused by LASIK procedure.