Researches On The Relationship Between Wavefront Aberrations And Visual Quality Of Human Eyes

Objective: The rapid development of refractive surgery has made people expectmore of it. People are not only satisfied with the correction of low order aberrations (defocus and regular astigmatism). Recent researches have focused on how to reduce the influence of high order aberrations (irregular astigmatism) on visual quality. In this paper, we study the relationship between high order aberrations and visual quality. This research may provide some reference for wavefront-guided ablation and further studies of myopia treatment with laser technology.Method: A total of 182 eyes from 91 patients were included. Patients' age rangedfrom 18 to 36 years(mean SE: 22.34 3.82 years).Preoperative spherical refraction ranged from 2 to 11 diopters (D)( mean SE: 5.02 2.01D) and cylinder refraction ranged from 0.25 to 5 diopters (D)( mean SE: 1.04 0.84D). Contrast sensitivity was measured (CSV-1000, Vector Vision, USA) under no-glare and glare condition. Corneal topography was evaluated (Orbscan II, Bausch &Lomb , USA) and wavefront aberrations were obtained (Allegretto Wavefront Analyzer, Lumenis, Germany).Results:1. When the pupil size is 4mm, only Z20 influences the irregularity of the cornea, linear regression equation is Irreg=5.713Z20+1.478. When the pupil is 5mm, Irreg=3.165Z20+3.315Z42+2.424. When the pupil size increases to 6mm, spherical aberration(Z40) is the main factor, linear regression equation is Irreg=5.576Z40+2.959 Z44+1.869. More higher order aberrations such as Z60, Z55,Z6-4 affect the Irreg when the pupil is 7mm and linear regression equation is Irreg= 10.851Z60+4.089 Z55+2.326 Z6-4+3.786.2. Under no-glare condition, high order aberrations do not affect contrast sensitivity(CS) when spatial frequency is 3cpd and only affect CS of 6cpd, 12cpd and 18cpd. Under glare condition, high order aberrations influence CS of 12cpd and 18cpd. And the items of acting aberrations reduce. Compared with no-glare condition, CS of 3cpd, 12cpd and 18cpd increase under glare condition. The difference between them is statistically significant(t values are 3.113, 3.016, 3.398 respectively and P values are 0.002, 0.003, 0.001).3. Sphere error is positively correlated with spherical-shape aberration(S4) and higher order aberrations 85, 85; correlation coefficients are 0.390(P<0.01)> 0.176(P<0.05), 0.408(P<0.01) respectively. Astigmatism also has weak positive correlation with S3,S4 ,S5 and S6 ; correlation coefficients are 0.248 (P<0.01 ), 0.175(P<0.05),0.206(P<0.05),0.213(P<0.05). The high- myopia group(sphere error 6.0D) has higher aberrations(S4,S5 ,S6 and total high-order aberration Sh) than the medium-myopia group and low-myopia group. The differences between them are of statistical significance(F=l 1.749 P<0.01; F=4.008 P<0.05; F=9.433 P<0.01; F=6.492 P<0.01). The group with less than 1.0D astigmatism has opposite spherical aberration(Z40) and less Z44 compared with the other two groups(astigmatism between l.0D and 2.0D, astigmatism 2.0D). The group with more than 2.0D astigmatism has higher aberrations (S3 , S4 , S5, S5 and Sh) than the other two groups.Conclusion:1. The irregularity of the cornea is affected by wavefront aberrations and the itemsare different for different pupil sizes. Low order aberrations are the main cause of the irregularity with small pupil size. When pupil is dilated, high order aberrations especially spherical aberrations (Z4 ) become the main cause.2. Under no-glare condition, high-order aberrations only influence contrast sensitivity of high spatial frequency and don't affect CS of low spatial frequency. The effect reduces under glare condition. And CS increases compared with no-glare condition.3. Low-order aberrations(sphere error and astigmatism) have positive correlation with high-order aberrations. The groups with high myopia or high astigmatism have more aberrations than the other groups with lower myopia and astigmatism.