Reserch On Visual And Optical Quality Evaluation Based On Wavefront Aberration And Modulation Transfer Function (MTF) Before And After Corneal Refractive Surgery

Section 1 Optical Quality Analysis after Surface Excimer Laser Ablation:Relationship between Wavefront Aberration and subepithelial HazePurpose:To investigated the relationship between the mild and moderate corneal haze and higher order distribution of wavefront aberration after surface excimer laser ablation.Methods:Ten eyes with corneal haze and twenty-six eyes without corneal haze 6 months or more after photorefractive keratectomy were analyzed. The wavefront aberrations were measured using a psychophysical wavefront sensor. Topography, PSF and MTF maps were obtained for equating optical image using NIDEK OPD-Scan.Results:The total higher-order aberration was slightly higher but no statistically significant in the corneal haze group than control group.. The ocular coma-like (3rd Third order) aberration showed higher than control group, spherical aberration (4th Fourth-order),however, was found lower than control group, The t-values are 1.05,-0.38,-1.10,-0.08, and -0.23, for 3rd,4th,5th,6th and 7th order respectively and no statistically significant. In term of Zernike coefficient, C3-1 andC31 showed greater mean RMS for haze group(0.33,0.35) than that for control group (0.26,0.23) (t=0.71,p=0.49;t=0.84,p=0.43). Z40, however,was less mean RMS for haze group(0.18) than that for control group(0.28), although still no statistically significant.Conclusion:Optical aberrations after PRK with corneal haze are given a various effects the amount and character of the higher-order aberration. In the corneal haze eye, higher coma might be caused by the slightly corneal wrinkled and less spherical aberration agreement with histological remodeling and stromal thickening with corneal haze after excimer laser ablation Section 2 Higher-order Aberration and Low Contrast Vision Function in Myopic Eyes at Mesopic ConditionPurpose:To investigate relationship between high-order aberration and low contrast visual acuity (VA) in myopic eye at mesopic condition.Methods:In this prospective observational case series. Fifty-two subjects (29 female, 23 male) of age 18-35 years were collected. Ocular higher-order aberration was measured in mesopic condition using the Hartman-shack wavefront analyzer and high (100%) and low contrast (25%,10%,5%) visual acuity was measured using Multi-Function Visual Acuity Tester at the same condition.Results:Multiple linear regression analysis revealed that spherical aberration were significantly associated with low contrast VA at low contrast level. The correlate coefficient of S4 were 0.419,0.315 and 0.393 at 25%,10% and 5% respectively (P =0.002,0.023,0.004). The correlate coefficient of C40 were 0.373 at 5% contrast level (P=0.006). However, coma and other higher order aberration didn't show the statistical correlation (P>0.05).Conclusion:There are relation between spherical-like aberration (S4) and spherical aberration(C40 of the eye and low contrast visual acuity. The larger spherical aberration is, the more significant the effect on lower contrast visual acuity is. Suggesting that the less spherical aberration may provides the optimal visual function at night condition. Section 3 Optical Quality Evaluation and Changes of MTF after Laser in Situ KeratomileusisPurpose:To investigate the changes of optical system and its characteristics in the Modulation Transfer Function (MTF) after laser in situ keratomileusis.Methods:Prospective observation cases series. A aberrometer with Hartman shark principle was used to measure the monochormatic aberration of 102 eyes. MTF of optical system were calculated at various pupil size (3,4,5,6 mm) respectively and compared at pre-post condition and between conventional and wavefront guide ablation.Results:There was a significant increase in MTF positively compared with preoperative value at all spatial frequency (5-60 cycles per degree, c/d), P<0.05. MTF value got more improved without spherical aberration than without coma aberration after surgery. There was significant different at a spatial frequency of 5 c/d. Higher MTF were showed in the WFG-LASIK group although there are no significant different between conventional LASIK group and WFG LASIK group. There are apparently change as compared to that for with high order aberration at high spatial frequency.Conclusions:With the optical benefits expected from correcting higher aberration such as spherical aberration, wavefront guide ablation have showed a potential benefit but it is still complex and need more expensive consideration. MTF is a sensitive in demonstrating the optical quality in refeactive surgery.