[Contrast sensitivity and higher order aberration after conventional LASIK treatment].

AIM

The aim of the prospective study was to evaluate photopic high-contrast visual acuity, mesopic contrast sensitivity, and high order aberrations, to compare changes and post-operative development of those parameters and to analyze the dependence among aberrations and contrast sensitivity after conventional LASIK treatment.

MATERIALS AND METHODS

The authors followed-up patients treated by means of refractive LASIK treatment during the period from November 2006 to November 2007. The authors analyzed 51 eyes (31 patients). The average age of the group was 28.5 +/- 5.4 years (range, 18 - 41 years), preoperative average spherical equivalent was -4.95 +/- 1.24 D (from -3 to -8,25 D). Before the treatment and 1, 3, 6, and 12 months after LASIK treatment we evaluated the visual acuity (Snellen optotypes), contrast sensitivity under mesopic circumstances (CSV-1000E, VectorVision) and monochromatic aberrations (aberometer Zywave, Bausch & Lomb).

RESULTS

One year after the treatment the average uncorrected visual acuity was 1.07 +/- 0.15, index of effectiveness 0.99, and index of safety 1.02. The contrast sensitivity was in month 12 significantly decreased comparing to the preoperative level at the frequency 12 c/deg, in other already tested frequencies after 3-6 moths did not differed from preoperative values. During the follow-up period the curvature of contrast sensitivity average values was in the upper half of the normal interval range. Conventional LASIK treatment significantly induced the higher order aberration (twice), as well as the spherical aberration (four times).The same level of higher order aberrations root mean square (HOA-RMS), or increased maximally by 0.1 microm was detected by 10 % of cases; the spherical aberration was, compared to the preoperative value, lower, or increased maximally by 0.05 microm in almost one half of the cases. The increase of the higher order aberrations depended directly proportionally to the preoperative value of the spherical equivalent. Before the treatment, the values of total aberrations correlated to the contrast sensitivity of low space frequencies; however, there was not found any correlation between the higher order aberrations and contrast sensitivity. Six months after the LASIK treatment the values of higher order aberrations correlated to the contrast sensitivity except of the lowest frequency tested. The higher order aberrations increased together with decreasing contrast sensitivity. The data from the one-year follow up control did not show statistically significant correlation between the contrast sensitivity and the higher order aberrations. There was not found any correlation between the contrast sensitivity and the spherical aberration at any follow-up control after the surgery.

CONCLUSION

Although after the conventional LASIK treatment the curve of mesopic contrast sensitivity was located in the upper half of the normal range, in the medial space frequency it remained decreased comparing to the preoperative stage. The induction of higher order aberrations was twice as much and was directly correlated to the degree of the laser correction. The spherical aberration was four-times higher comparing to the preoperative values and was independent to the level of the initial refractive error. Significant correlation between the contrast sensitivity and the higher order aberrations was not proven.