Repeatability of a commercially available adaptive optics visual simulator and aberrometer in normal and keratoconic eyes

Purpose: To evaluate the repeatability of aberration measurement obtained by Hartmann- Shack aberrometer combined with an visual adaptive optics (VAO) simulator in normal and keratoconic eyes.
Methods: Fifty normal eyes and forty-two eyes of grade I and II keratoconus, as per the Amsler-Krumeich classification, were included in the study. To evaluate the repeatability, three consecutive measurements of ocular aberrations were obtained by a single operator. Zernike analyses up to fifth order for a pupil size of 4.5mm were performed. Statistical analyses included the intra-class correlation coefficient (ICC) and within-subject standard deviation (SD).
Results: For intra-session repeatability, ICC value for sphere and cylinder was 0.94 and 0.93 in normal eyes, respectively. The same was 0.98 and 0.97 in keratoconic eyes, respectively. The ICC for root mean square of higher order aberration (HOARMS) was 0.82 in normal and 0.98 in keratoconus eyes. For third order aberrations (trefoil and coma), the ICC values were >0.87 for normal eyes and >0.92 in keratoconus. The ICC for spherical aberration was 0.92 and 0.90 in normal and keratoconus eyes, respectively.
Conclusions: VAO provided repeatable aberrometry data in both normal and keratoconic eyes. For most of the parameters, the repeatability in early keratoconus eyes was somewhat better than the normal individuals. The repeatability of the Zernike terms was acceptable for third order (trefoil and coma) and spherical aberrations. Therefore, VAO was a suitable tool to perform repeatable aberrometric measurements.