Abstract
Purpose :
To determine the repeatability and accuracy of corneal astigmatism measured with a spectral-domain optical coherence tomography (SD-OCT).
Methods :
The SD-OCT (Avanti, Optovue, Inc) with a speed of 70,000 axial-scans/second and an axial resolution of 5 µm was used. The cornea of 20 pseudophakic eyes with nontoric monofocal intraocular lens were imaged using a radial scan pattern that performs cross-sectional OCT in 16 meridians along the central 5 mm centered on the pupil. Net corneal power was calculated in each meridian from the anterior and posterior corneal curvature. Fourier series harmonic analysis was applied to the meridional corneal power profile to determine the net corneal astigmatism. Two OCT scans per eye were acquired to estimate the repeatability by pooled standard deviation (SD). The true net power output of Scheimpflug imaging topography (Pentacam, Oculus Optikgerate GmbH) was used for comparison purposes. Manifest refraction was performed with a phoroptor and converted to the corneal plane.
Results :
OCT measured net corneal astigmatism had a repeatability of 0.17 D, 0.14 D, 0.24 D for cardinal component, oblique component, and cylinder magnitude, respectively. There was a small against-the-rule astigmatism bias (p >0.05, paired t-test) for both OCT and Scheimpflug, compared to MR (Table 1). Referenced to MR, OCT astigmatism measurement was closer than Scheimpflug astigmatism. The magnitude of the vector differences was 0.25 ± 0.60 D for OCT and 0.30 ± 0.66 D for Scheimpflug. The Pearson correlation coefficient (cardinal, oblique) for OCT v. MR was 0.567 (p=0.09), 0.590 (p=0.006), and for Scheimpflug v. MR was 0.589 (p=0.06), 0.479 (p=0.032).
Conclusions :
OCT net corneal astigmatism measurement has good repeatability. Compared to Scheimflug, OCT astigmatism measurement agreed better with MR.
This is a 2020 ARVO Annual Meeting abstract.