Objective Assessment of Optical Quality in Mild Keratoconus with a Double-Pass System

Objective: To analyze the difference in optical quality between a normal cornea and keratoconus using an optical quality analysis system (OQAS). Methods: This cross-sectional study included 32 normal eyes and 27 keratoconus eyes. Optical qualities were measured by OQAS. Modulation transfer function cutoff frequency (MTFcutoff), Strehl ratio and OQAS values (OV-100, OV-20, OV-9) in artificial pupil diameters of 3 mm, 4 mm and 5 mm were analyzed by independent t test or Mann-Whitney U test, the difference among groups was analyzed by ANOVA for repeated measurement and Bonferroni post hoc t test. Results: MTFcutoff, Strehl ratio and OQAS values of the keratoconus group in artificial pupil diameters of 3 mm, 4 mm and 5 mm were all lower than those of the control group (3 mm: t=6.658, 6.695, 6.660, 6.493, 6.778; 4 mm: t=7.106, 6.567, 7.109, 6.802, 6.788; 5 mm: t=6.148, 7.254, 6.158, 6.446, 7.210; all P<0.001). Both in the control group and in the keratoconus group, the MTFcutoff, Strehl ratio, OV-100, OV-20 and OV-9 varied from artificial pupil diameters (control group: F=42.205, 28.335, 42.559, 32.621, 30.372; keratoconus group: F=15.732, 11.533, 15.625, 13.870, 10.495; all P<0.001). Conclusions: The optical qualities of keratoconus measured by OQAS are worse than normal eyes. Both in keratoconus and normal eyes, the optical qualities decline as pupil size increases. Key words: keratoconus; optical quality; pupil; double-pass