Accuracy of OCT-derived net corneal astigmatism measurement

Abstract

Purpose: To assess the repeatability and accuracy of corneal astigmatism measurement with a spectral-domain optical coherence tomography (OCT) system (Avanti, Optovue) and compare them with Scheimpflug imaging (Pentacam HR, Oculus) and swept-source optical biometry (IOLMaster 700, Carl Zeiss Meditec AG).

Setting: Casey Eye Institute, Oregon Health & Science University, Portland, Oregon.

Design: Prospective cross-sectional observational study.

Methods: 60 pseudophakic eyes with monofocal nontoric intraocular lens that previously had refractive surgery were analyzed. To assess accuracy, simulated keratometry (SimK) and net corneal astigmatism, obtained from each device, were compared with subjective manifest refraction astigmatism. Repeatability for corneal astigmatism was assessed for OCT and Pentacam HR by the coefficient of repeatability from 3 repeated measures.

Results: Compared with manifest refraction, SimK readings produced with-the-rule astigmatic bias that was reduced for net astigmatism for the 3 devices. Except for OCT net astigmatism, all instruments significantly overestimated the magnitude of the astigmatism (linear mixed-effects model [LMM], P < .05). OCT net astigmatism showed the highest accuracy for manifest astigmatism prediction with the smaller 95% confidence ellipse for the mean difference vector. OCT net mean absolute difference was 0.57 diopters (D), significantly smaller than that of the other modalities (LMM, P < .05). Net corneal astigmatism measured with OCT showed the best repeatability (coefficient of repeatability = 0.29 D).

Conclusions: OCT has the capability to measure net corneal astigmatism with higher precision and accuracy than Pentacam HR Scheimpflug imaging and IOLMaster 700 swept-source optical biometry in postrefractive subjects.