The effect of corneal wavefront aberrations on corneal pseudoaccommodation.
OBJECTIVE
To determine the effect on corneal pseudoaccommodation of anterior corneal wavefront aberrations in normal corneas and corneas with prior myopic or hyperopic photorefractive keratectomy (PRK) or laser-assisted in situ keratomileusis (LASIK).


METHODS
Theoretical study.


METHODS
In 220 normal eyes, 102 myopic-PRK eyes, and 106 hyperopic-LASIK/PRK eyes, anterior corneal higher-order aberrations (HOAs, third to sixth order, 6- and 4-mm pupils) were computed from the Atlas corneal elevation data using the VOL-CT program. Using the ZernikeTool, corneal optical image quality was evaluated by the polychromatic modulation transfer function with Stiles-Crawford effect. Defocus from -3.0 diopters (D) to +3.0 D was added to corneal HOAs, and depth of focus was defined as the ranges over which the polychromatic modulation transfer function maintains 80% of the peak value (DOF80) and 50% of the peak value (DOF50). The depth of focus values between groups were compared, stepwise multiple regression was used to assess if any Zernike terms significantly contributed to the depth of focus, and correlation analysis was performed to evaluate the correlation between depth of focus and corneal HOAs.


RESULTS
The depth of focus varied widely between corneas, especially in corneas with prior hyperopic-LASIK/PRK. For 6-mm pupil, mean depth of focus values in myopic-PRK and hyperopic-LASIK/PRK corneas were significantly greater than those for normal corneas, and for 4-mm pupil, depth of focus values in hyperopic-LASIK/PRK corneas were greater than those in normal and myopic-PRK corneas. Zernike terms significantly contributing to both DOF80 and DOF50 were fourth- and sixth-order spherical aberration and fourth- and sixth-order astigmatism in normal corneas, third-order vertical coma and fourth-order tetrafoil in myopic-PRK corneas, and third-order vertical coma and fourth-order astigmatism in hyperopic-LASIK/PRK corneas. Depth of focus had weak to moderate positive correlation with HOAs (Pearson correlation coefficient r ranged from 0.300 to 0.583).


CONCLUSIONS
These theoretical calculations suggest that certain corneal wavefront aberrations affect corneal pseudoaccommodation. To predict corneal pseudoaccommodation, the most important Zernike term is spherical aberration in normal eyes and coma in eyes with prior laser corneal surgery.
Cullen Eye Institute, Department of Ophthalmology, Baylor College of Medicine, Houston, Texas 77030, USA. yeu@bcm.edu
Elizabeth
E
Yeu
Li
L
Wang
Douglas D
DD
Koch
D000065:Accommodation, Ocular / Q000502:physiology*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002387:Cataract Extraction; D003315:Cornea / Q000503:physiopathology*; D057108:Corneal Wavefront Aberration / Q000503:physiopathology*; D003867:Depth Perception / Q000502:physiology; D005260:Female; D006801:Humans; D006956:Hyperopia / Q000601:surgery; D020731:Keratomileusis, Laser In Situ; D019654:Lens Implantation, Intraocular; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000601:surgery; D018903:Photorefractive Keratectomy; D019591:Pseudophakia / Q000503:physiopathology*; D055815:Young Adult