Comparison of Corneal Topographic Measurements by Placido ring and Anterior Segment OCT in Eyes With Keratoconus

• Published in: JAPANESE ORTHOPTIC JOURNAL Vol. 44; pp. 149 - 156
• Main Authors: Yamamura, Aya, Suzuki, Sayori, Noritake, Rina, Okada, Akane, Uno, Yunako, Kataoka, Takahiro, Kojima, Takashi
• Format: Journal Article
• Language: Japanese
• Published: JAPANESE ASSOCIATION OF CERTIFIED ORTHOPTISTS 2015
• Subjects: anterior segment optical coherence tomography; corneal topography; keratoconus; placido ring
• ISSN: 0387-5172; 1883-9215
• DOI: 10.4263/jorthoptic.044F016

[Purpose] To compare the corneal topographic measurements taken by a placido-ring system and anterior segment optical coherence tomography (OCT) in keratoconic eyes. [Subjects and Methods] Seventy eyes of 39 patients (24 males, 15 females; average age, 41±19.2 years) with keratoconus were enrolled in the study. Based on the Amsler-Krumeich classification, the eyes were categorized into the low-stage (stage 1 and 2) and high-stage (stage 3 and 4) groups. Keratometric values of axial power map, average corneal refractive power, corneal astigmatism, and asymmetric/higher-order irregularity components by Fourier analysis in the 3 mm from the central cornea were assessed and compared between a placido-ring system (TMS-4 Advance, TOMEY Co.) and an anterior segment OCT system (CASIA, TOMEY Co.). Wilcoxon signed rank test was performed for statistical analysis, and a p-value less than 0.05 was considered statistically significant. [Results] The respective average differences (TMS minus CASIA) in the low- and high-stage groups were 0.55±1.0 D (P = 0.049) and 2.87±0.7 D (P = 0.005) for corneal astigmatism, and 0.18±1.3 D (P = 0.02) and 0.72±0.4 D (P = 0.004) for higher-order irregularity component. The measurements by the TMS-4 were significantly greater than those by the CASIA. OCT system in both groups. On the other hand, the average difference in asymmetric component was -1.52±0.8 D in the high-stage group, showing a significantly greater measurement by the CASIA (P = 0.03). [Conclusion] In keratoconic eyes, differences in the corneal topographic measurements were observed between the placido-ring and anterior OCT systems. This suggested that measurements using the same system are preferred when assessing the changes of corneal refractive power over time.