Corneal irregular astigmatism and contrast sensitivity after photorefractive keratectomy.

OBJECTIVE

To investigate the relation between contrast sensitivity and corneal irregular astigmatism in eyes after photorefractive keratectomy (PRK).

DESIGN

Prospective observational case series.

PARTICIPANTS AND CONTROLS

Seventy-nine eyes without corneal haze 6 months or more after PRK and 30 normal control eyes.

METHODS

Videokeratography was taken with TMS-1 (Computed Anatomy Inc. New York, NY), and contrast sensitivity for day and night vision was measured using a Multivision Contrast Tester 8000 (Vistech Consultants, Inc., Dayton, OH).

MAIN OUTCOME MEASURES

Regular and irregular astigmatism (asymmetry and higher order irregularity components) were computed using Fourier series harmonic analysis of the videokeratography data. Area under the log contrast sensitivity function (AULCSF) was calculated from the contrast sensitivity data taken at five spatial frequencies.

RESULTS

After PRK, AULCSFs were significantly smaller for day vision (P = 0.007, unpaired t test) and night vision (P = 0.020) compared with normal controls. AULCSFs for day vision were significantly negatively correlated with asymmetry (Pearson's correlation coefficient, R = -0.23, P = 0.049) and higher order irregularity (R = -0.33, P = 0.004) components but not with the regular astigmatism component (P > 0.3). AULCSF for night vision correlated significantly with asymmetry (R = -0.31, P = 0.013) and higher order irregularity (R = -0.30, P = 0.016) components but not with the regular astigmatism component (P > 0.3).

CONCLUSIONS

Corneal irregular astigmatism after PRK significantly influences contrast sensitivity.