Posterior and total corneal astigmatism measured with optical-coherence-tomography-based biometer and dual-Scheimpflug analyzer.

PURPOSE To compare corneal astigmatism obtained from OCT-based biometer (OCT) and Dual Scheimpflug Analyzer (DSA). SETTING Cullen Eye Institute, Baylor College of Medicine, Houston, TX. DESIGN Retrospective case series. METHODS We reviewed consecutive cases with both OCT and DSA measurements. Three parameters were analyzed with OCT and DSA: 1) standard keratometric astigmatism (K vs. SimK), 2) posterior corneal astigmatism, and 3) total corneal astigmatism (TK vs. TCP). We compared the magnitudes of corneal astigmatism obtained from the two devices. Vector analysis was used to assess differences in corneal astigmatism between devices. RESULTS We measured 530 corneas in 530 patients. Compared with the DSA, the OCT produced a lower mean magnitude of posterior corneal astigmatism (-0.19 vs. -0.29 D) and a higher percentage of eyes with magnitude ≤0.25 D (75.5% vs. 41.9%) (P<0.05). Comparing TK and TCP, we found: 1) TK was greater in magnitudes (1.03 vs. 0.98 D); 2) 84.3% of eyes had differences in magnitude of ≤0.50 D; 3) in eyes with TK astigmatism ≥0.5 D, 34.5% and 60.1% of eyes had differences in steep meridian of ≤5° and ≤10°, respectively, and 4) 59.2% of eyes had vector differences of ≤0.50 D. In WTR and ATR eyes, respectively, the vector differences between TK and TCP were 0.16 D@83° and 0.17 D@12°, and in posterior corneal astigmatism, 0.06D@173°; and 0.15 D@175°. CONCLUSION There were clinically significant differences in total corneal astigmatism obtained from OCT and DSA devices. Compared to DSA, the OCT produced lower values for posterior corneal astigmatism.