PURPOSE. This experiment was to determine the aberrations found in keratoconic eyes, with and without RGP contact lens correction.
METHOD. Three aberration measurements (COAS Wavefront Science Inc.) were taken on twenty eyes of ten diagnosed keratoconic subjects (7 male, 3 female) with a mean age of 39.2 (range: 25-63), and a mean steep simulated keratometry reading of 47.68±4.3 (range: 41.2-59.5). Measurements were taken for all subjects without contact lens correction and for 13 of these subjects with their habitual gas permeable contact lens correction. Data were analyzed for a 4mm pupil diameter, and wavefront variances were changed to equivalent power in diopters (Me) using the equation: Me=(4*sqrt(3)*pi*RMS error)/pupil area.
RESULTS. As expected, these keratoconic subjects possessed significant defocus and astigmatism. The oblique astigmatism (J45=0.53±0.31D) was greater than expected in normals, but about the same magnitude as horizontal/vertical astigmatism (J0= 0.59±0.59D). Third order aberration, dominated by vertical coma (Z3\+1) was the second most pronounced aberration in all keratoconic eyes (total third=0.56±0.3D, vertical coma (Z3\+1)=0.41±0.32D, compared with 0.18D and 0.06D in normal eyes respectively). Spherical aberration was relatively small in these subjects (total fourth=0.17±0.07D, spherical aberration (Z4\0)=0.03±0.04D, compared with 0.11D and 0.08D in normal eyes respectively). The contact lens correction effectively reduced defocus and astigmatism, and in most eyes significantly reduced the amount of vertical coma (total third: from 0.56±0.30D to 0.28±0.12D, vertical coma: from 0.41D±0.32D to 0.15±0.11D). Contact lens correction only had a small effect on horizontal coma (from 0.15±0.12D to 0.12±0.08D), spherical aberration (from 0.03±0.04D to 0.02±0.03D), and total fourth order aberration (from 0.17±0.07D to 0.10±0.05D).
CONCLUSIONS. Although keratoconic subjects possess significantly higher amounts of oblique astigmatism and vertical coma than the normal population, standard gas permeable contact lens corrections successfully reduce this in most subjects.