[Visual quality evaluation on changes of MTF and wavefront aberration after laser in situ keratomileusis].

Objective: To investigate the changes of the Modulation Transfer Function (MTF) and its effect on visual and optical quality with or without low and higher order wavefront aberration after conventional and wavefront guild laser in situ keratomileusis.

Methods: It was a comparative case series. An aberrometer with Hartmann-shark sensor was used to measure the monochromatic aberration of eyes. One hundred and two cases entered the study; 38 cases were randomized to LASIK and 64 were randomized to WFG-LASIK. MTFs of optical system were calculated at various pupil size (3, 4, 5 and 6 mm) respectively and compared pre and 3 month postoperatively between conventional and wavefront guide ablation with or without higher order aberration.

Results: There was a significant increase in MTF positively compared with preoperative values at all spatial frequency (5-60 cycles per degree, c/d ), P < 0.05. MTF values got more improvement without spherical aberration than without coma aberration after LASIK surgery and there was significant different at a spatial frequency of 5 c/d. Higher MTFs were showed in the WFG-LASIK group although there were no significant difference between conventional LASIK group and WFG-LASIK group. However, there were apparently changed without high order aberration as compared to that with high order aberration at all spatial frequency (5-60 c/d. ) in WFG-LASIK group and higher MTFs were showed in the WFG-LASIK group compared with conventional LASIK group and there were significant different (P < 0.05) by calculation and evaluation.

Conclusion: Spherical aberration have more negative role on visual quality than coma aberration after LASIK surgery. With the optical benefits expected from correcting higher aberration, wavefront guide ablation have shown a great benefit for low and high order aberration but it still leave a small amount of high order aberration and need further investigation. MTF is a sensitive and extensive in demonstrating the optical quality in refractive surgery.