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A comparison between subjective refraction and aberrometry-derived refraction in keratoconus patients and control
Amit Jinabhai1, Clare O'Donnell, Hema Radhakrishnan
1Faculty of Life Sciences, The University of Manchester, Manchester, United Kingdom.
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.
