A Comparative Study Of Visual Performance Before And After LASIK And LASEK For Low To Moderate Myopia

Purpose:To evaluate the visual performance including the change of contrast sensitivity and visual acuity pre-postoperative laser in situkeratomileu-sis (LASIK) and Laser subepithelial keratomileusis(LASEK) for low to moderate myopia.Methods:Fifty two patients (112 eyes) that matches the low to moderate myopia were randomly divided into two groups (LASIK group and LASEK group),26 patients (52 eyes) in each group. Routine examination including visual acuity, objective refraction, non-contact tonometry, anterior segment examination, funds examination and corneal topography were taken preoperational and in lm,3m,6m,12m postoperatively. The contrast sensitivity was also test with Optec 6500 Vision Tester pre-postively. Contrast sensitivity test cards (FACT) were examined including night, night plus peripheral glare, day, day plus peripheral glare under the conditions of the four contrast sensitivity.Results:1.In LASEK group, Haze appeared in patients at the ratio of 10.71%.2. There was no statistically significant difference on BCVA between LASEK group and LASIK pre-postoperatively (p> 0.05).3. Contrast sensitivity test (1) In LASIK group, each segment CSVA spatial frequencies were significantly lower than that of preoperative values 1m after operation (p <0.01); The 6 frequency bands was lower than that of preoperational in 3m post-operation (p<0.05) while other spatial frequencies were significantly lower than preoperative levels (p<0.01); There was no statistically significant difference on segment of the spatial frequency value in 6m and 12m after operation; (2) In LASEK group, compare to the pre-operation, all CSVA values of spatial frequency band were significantly lower in lm post-operation (p <0.01). The 1.5 band CSVA value was significantly lower in 3m after operation (p<0.01) while the 3 band lower than that of pre-operation (p<0.05). But values in other special frequency band are not significantly different between pre-postoperative (p> 0.05); There were no statistically significant difference on segment of the spatial frequency value of CSVA in 6m and 12m after operation (p> 0.05); (3) Comparation of LASIK group and LASEK group: There was no significant difference on the spatial frequencies CSVA between these two group before operation (p> 0.05); compare to LASEK group, there was significant difference on all spatial frequencies in 3m post-operation of LASIK group (p<0.05); and there were no statistically significant difference on all spatial frequencies between the two groups in 6m and 12m after operation (p> 0.05).Conclusions:(1) In LASEK group, Haze appeared in patients at the ratio of 10.71%, which indicated that there was much risk for the post-operation of causing haze. (2) The postoperative visual acuity would be the same as or better than the best corrected visual acuity before operation, whichever procedure be chosen, LASEK or LASIK; (3) The visual contrast sensitivities (CSVA value) of low to moderate myopia were lower than preoperative levels in lm and 3m after operation both in LASIK and LASEK group, and would be returned gradual in 6m; (4) There was no significantly difference on visual contrast sensitivity (CSVA value) between the two group in lm post-operation. From the 1m after surgery, spatial frequency contrast sensitivity of LASEK group was higher than that of LASIK group. There are larger fluctuations of the spatial frequencies of visual contrast sensitivity (CSVA value) in LASIK group than that of LASEK group in 3m after operation.