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Objective evaluation of refractive data and astigmatism: quantification and analysis.

ABSTRACT: The aim of this study was to present methods to improve the analysis of refractive data. A comparison of methods is used to analyse refractive powers using individual powers and aggregate data. Equations are also developed for the representation of the average power of a lens or refractive data as a univariate measure, which includes spherical, coma, and/or other aberrations. The equations provide a precise representation of refractive power, which is useful for comparing individual and aggregate data. Average lens power in the principal meridian can be adequately computed as can the average lens power through orthogonal and oblique meridians, providing a good univariate representation of astigmatism and refractive power. Although these formulae are perhaps not as easy to use as, for example, the spherical equivalent, they are more precise and superior in principle involving fewer approximations and are not subject to systematic bias. These effects are of significance when dealing with high-powered lenses such as intraocular lenses or the cornea. They need to be taken into account particularly for calculations of intraocular lens power, toric intraocular lenses, and cornea refractive surgery, especially if outcomes are to be improved. Such issues are of particular importance when dealing with aggregate data and determining statistical significance of treatment effects.

SUBMITTER: Kaye SB

PROVIDER: S-EPMC3930272 | biostudies-other | 2014 Feb

REPOSITORIES: biostudies-other

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Project description:This study aimed to assess refractive astigmatism, in phaco-canaloplasty (PC) vs phaco-non-penetrating deep sclerectomy (PDS) in a randomized, prospective study within 24 months. Patients were randomized pre-operatively, 37 underwent PC and 38 PDS. The following data was collected: BCVA, IOP, number of antiglaucoma medications, refraction with autokeratorefractometry. The assessment of astigmatism was simple arithmetic and vector analysis (calculations included cylinder with axis in form of centroids) and included double angle plots and cumulative refractive astigmatism graphs. Pre-operative mean BCVA in PC was 0.40 ± 0.43 and was comparable to BCVA in PDS 0.30 ± 0.32logMAR (P = 0.314). In the sixth month follow-up, mean BCVA showed no difference (P = 0.708) and was 0.07 ± 0.13 and 0.05 ± 0.11, respectively. However, 2 years after the intervention mean BCVA was better in PC 0.05 ± 0.12 than in PDS 0.12 ± 0.23 and it was statistically significant (P = 0.039). Mean astigmatism in PC at baseline was 1.13 ± 0.73Dcyl, at 6 months it was 1.09 ± 0.61 and at 2 years 1.17 ± 0.51. In PDS at baseline 1.35 ± 0.91 at 6 months 1.24 ± 0.86 and at 2 years 1.24 ± 0.82. There were no differences between the groups in mean astigmatism throughout the study. Centroids (mean of a cylinder with axis) in PC were pre-operatively 0.79D@172˚ ± 1.10Dcyl, at 6 months 0.75D@166˚ ± 1.01 and at 24-months 0.64D@164˚ ± 1.11 and in PDS pre-operatively 0.28D@10˚ ± 1.63D at 6 months 0.26D@11˚ ± 1.5 and at 24-months 0.47D@20˚ ± 1.43. The direction of mean astigmatism was against the rule in all analyzed time points. The mean baseline IOP in PC was 19.4 ± 5.8 mmHg and 19.7 ± 5.4 mmHg in PDS(P = 0.639). From the 6-month IOP was lower in PC, at 24-months it was 13.8 ± 3.3 mmHg in PC and 15.1 ± 2.9 mmHg in PDS(P = 0.048). In both groups preoperatively patients used median(Me) of three antiglaucoma medications(P = 0.197), at 24-months in PC mean 0.5 ± 0.9 Me = 0.0 and 1.1 ± 1.2 Me = 1.0 in PDS(P = 0.058). Both surgeries in mid-term observation are safe and effective. They do not generate vision-threatening astigmatism and do not even change the preoperative direction of mean astigmatism. Refractive astigmatism is stable throughout the observation.

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Objective evaluation of refractive data and astigmatism: quantification and analysis.

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