Optical consequences of asymmetries in normal corneas.
A survey of videokeratographs of normal corneas shows many with substantial peripheral asymmetries. For sufficiently large pupils (5.5 mm in this study) these asymmetries lead to coma-like axial aberrations large enough to produce measurable losses in vision in a number of cases. Starting from the output of a videokeratographic instrument, a method of estimating the optical effects of corneal asymmetries using Zernike circle polynomials is outlined. It is further shown that in a first approximation corneal asymmetries can be identified with the primary aberration coma and that this aberration is approximately due to a uniform gradient of refractive power across the cornea. Calculations for a representative case predict that a significant improvement in modulation transfer would follow from correction of this aberration.
Hemenger
R P
RP
Southern California College of Optometry, Fullerton, CA 92631, USA.
Tomlinson
A
A
Oliver
K
K
D000293:Adolescent; D000328:Adult; D003315:Cornea / Q000033:anatomy & histology*; D003627:Data Interpretation, Statistical; D006801:Humans; D012029:Refraction, Ocular; D014786:Vision Disorders / Q000209:etiology* / Q000503:physiopathology