A Comparison between Subjective Refraction and Aberrometry-Derived Refraction in Keratoconus Patients and Control Subjects

Purpose: This study compares the differences in the magnitude of the subjective refraction and three aberrometry-derived refractions along with visual acuity achieved with these refractions in a group of keratoconic patients and age-matched normal subjects. Materials and Methods: Subjective refraction and Hartmann-Shack aberrometry was performed on six keratoconus patients and 12 normal subjects. In addition, the logMAR visual acuity achieved using the subjective and aberrometry auto-refraction data were measured in the six keratoconic subjects. Results: The subjective and aberrometry-derived spherical equivalent refraction data were significantly different in the keratoconus group (p = 0.015) but not in the normal group (p = 0.10). In the keratoconic patients, subjective refraction data gave better logMAR acuity than the aberrometry-derived auto-refraction data. The magnitudes of vertical coma and higher-order RMS (root mean square) error showed significant correlations with the subjective refraction logMAR visual acuities. Significant correlations were found between the magnitudes of manifest vertical coma and higher-order RMS error and the difference in the M (the mean equivalent sphere) power vector terms between the subjective and aberrometry-derived auto-refraction data in the keratoconic group. Conclusions: The subjective and aberrometry-derived spherical equivalent refraction data were significantly different in the keratoconus group. The larger the magnitude of the higher-order aberrations in keratoconic eyes, the poorer the subjective refraction logMAR acuity and the larger the difference between the subjective and aberrometry-derived M power vector terms. Further investigation into deriving objective refraction data from aberrometry measurements is warranted in keratoconus.