Validity of autorefractor based screening method for irregular astigmatism compared to the corneal topography-a cross sectional study

AIM：To present a method of screening for irregular astigmatism with an autorefractor and its determinants compared to corneal topography.METHODS：This cross-sectional validity study was conducted in 2013 at an eye hospital in Spain.A tabletop autorefractor（test 1）was used to measure the refractive status of the anterior surface of the cornea at two corneal meridians of each eye.Then corneal topography（test 2）and Bogan’s classification was used to group eyes into those with regular or no astigmatism（GRI）and irregular astigmatism（GRII）.Test 1 provided a single absolute value for the greatest cylinder difference（Vr）.The receiver operating characteristic（ROC）were plotted for the Vr values measured by test 1 for GRI and GRII eyes.On the basis a Vr value of 1.25 D as cut off,sensitivity,specificity were also calculated.RESULTS：The study sample was comprised of 260 eyes（135 patients）.The prevalence of irregular astigmatism was 42%[95%confidence interval（CI）：36,48].Based on test 2,there were 151 eyes in GRI and 109 eyes in GRII.The median Vr was 0.75 D（25%quartile,0.5 D）for GRI and1.75 D（25%quartile,1.25 D）for GRII.The area under curve was 0.171 for GRI and 0.83 for GRII.The sensitivity of test I was 78.1%and the specificity was 76.1%.CONCLUSION：A conventional autorefractor can be effective as a first level screening method to detect irregular corneal astigmatism in places where corneal topography facilities are not available.

Vector analysis of Contoura Vision for the correction of myopia and myopic astigmatism

AIM: To evaluate the visual outcomes of Contoura Vision(CV) with automatic eye tracking system in eyes with myopia and myopic astigmatism.METHODS: This prospective study included 160 eyes(80 patients) with moderate myopia and irregular astigmatism between January and August 2018. Subjects were randomly divided into CV group(80 eyes) that under went CV femtosecond laser-assisted in situ keratomileusis(FS-LASIK) and a control group(80 eyes) that underwent wavefrontoptimized FS-LASIK. Visual outcomes and astigmatic vector analysis were evaluated and compared between preoperatively and 3 mo postoperatively. RESULTS: Basic details were similar in both groups(P>0.05). At 3 mo postoperatively, uncorrected distance visual acuity was 20/16, 20/20, and 20/25 in 24, 76, and 80 eyes of patients in CV group, respectively. The CV group was better in predictability of astigmatism correction at 3 mo postoperatively. In CV group, 64 eyes had deviation of astigmatic axis within 15° and 28 eyes had deviation of astigmatic axis within 5°, both were better than those in the control group. The number of eyes with residual astigmatism within 0.5 D were less in CV group(48 eyes) than the control group(40 eyes). Compared with the preoperative, C7 significantly reduced to 0.056±0.030 in CV group at 3 mo after the procedure(P<0.05), and were significantly lower than those in the control group(P<0.05).CONCLUSION: CV with automatic eye tracking system is safe and effective for the correction of myopia and myopic astigmatism.

Assessment of refractive astigmatism and simulated therapeutic refractive surgery strategies in coma-like-aberrations- dominant corneal optics

Background:The aim of the study is to raise the awareness of the influence of coma-like higher-order aberrations(HOAs)on power and orientation of refractive astigmatism(RA)and to explore how to account for that influence in the planning of topography-guided refractive surgery in eyes with coma-like-aberrations-dominant corneal optics.Methods:Eleven eyes with coma-like-aberrations-dominant corneal optics and with low lenticular astigmatism(LA)were selected for astigmatism analysis and for treatment simulations with topography-guided custom ablation.Vector analysis was used to evaluate the contribution of coma-like corneal HOAs to RA.Two different strategies were used for simulated treatments aiming to regularize irregular corneal optics:With both strategies correction of anterior corneal surface irregularities(corneal HOAs)were intended.Correction of total corneal astigmatism(TCA)and RA was intended as well with strategies 1 and 2,respectively.Results:Axis of discrepant astigmatism(RA minus TCA minus LA)correlated strongly with axis of coma.Vertical coma influenced RA by canceling the effect of the with-the-rule astigmatism and increasing the effect of the against-the-rule astigmatism.After simulated correction of anterior corneal HOAs along with TCA and RA(strategies 1 and 2),only a small amount of anterior corneal astigmatism(ACA)and no TCA remained after strategy 1,while considerable amount of ACA and TCA remained after strategy 2.Conclusions:Coma-like corneal aberrations seem to contribute a considerable astigmatic component to RA in eyes with coma-like-aberrations dominant corneal optics.If topography-guided ablation is programmed to correct the corneal HOAs and RA,the astigmatic component caused by the coma-like corneal HOAs will be treated twice and will result in induced astigmatism.Disregarding RA and treating TCA along with the corneal HOAs is recommended instead.