Abstract
Purpose::
We developed a new analysis system for quantitative assessment of corneal irregular astigmatism using autorefractive keratometer. The aim of the present study wasto evaluate the availability of this system to quantitate corneal irregular astigmatism.
Methods::
A software was developed for analysis of the asymmetry index (KAI) and irregularity index (KRI) over a region extending approximately 3 mm of the corneal center, based on data of the corneal center obtained from the alignment light source and the corneal shape obtained from eight corneal light sources using an autorefractive keratometer (RC-5000, Tomey Corporation, Nagoya, Japan), which was commercially available. Using this software, KAI and KRI were compared with the results of Fourier analysis of cornel topography (TMS-4, Tomey Corporation, Nagoya, Japan) in 565 eyes of 320 subjects, including normal cornea and eyes with irregular astigmatism ranging from mild to severe. After informed consent was obtained, all patients underwent the measurements of both RC-5000 (KAI and KRI) and TMS-4 (Fourier analysis).
Results::
By TMS-4 Fourier analysis, the asymmetric component was 0.78 ±1.18 D (mean ± standard deviation), which showed a significant correlation with KAI obtained with RC-5000 (r = 0.9510, p < 0.001). The higher order irregularity component was 0.21 ±0.26 D, which showed a significant correlation with KRI (r = 0.7783, p < 0.001).
Conclusions::
RC-5000 (KAI and KRI) and TMS-4 (Fourier analysis) showed a significant correlation in the measurements of corneal irregular astigmatism. The new software on RC-5000 system appears to be useful as a simple and easy screening method of corneal irregular astigmatism, such as mild and early keratoconus.
Keywords: astigmatism • keratoconus • refraction