Correlation of wavefront data and corneal asphericity with contrast sensitivity after laser in situ keratomileusis for myopia.
OBJECTIVE
To investigate the relationship between contrast sensitivity (CS), Zernike wavefront aberrations (WFA), and asphericity after laser in situ keratomileusis (LASIK) for myopia.


METHODS
LASIK was performed using the Nidek EC-5000 excimer laser with custom aspheric transition zone (CATz) ablations. Total and high order (HO) WFA of 71 eyes (37 patients) undergoing LASIK in March 2003 were measured before and at 1 month postoperatively with the Nidek OPD-Scan aberrometer at a 4-mm pupil entrance; asphericity was measured at 6 mm (Q index). Preoperative and 1 to 3-month postoperative contrast sensitivity were evaluated with the Vector Vision CSV-1000 at 3, 6, 12, and 18 CPD; the Area Under the Log Contrast Sensitivity Function (AULCSF) was calculated. Uncorrected-visual acuity (UCVA) was evaluated.


RESULTS
One month after LASIK, CS decreased significantly at 6 CPD and above (P<.05), then returned to normal at 3 months (P=.33). Postoperative AULCSF correlated with patient age (P=.04) but not with total WFA (P=.13), HO WFA (P=.50), or asphericity (P=.22). Postoperative Logmar UCVA correlated with postoperative total and HO WFA (P<.05). Postoperative total WFA correlated with spherical equivalent refraction (P<.0001); HO WFA correlated with Strehl ratio (P=.004) and asphericity (P=.03). The HO WFA increase was 0.065 microm (P<.05) and did not correlate with preoperative refraction (P=.40). Increase in asphericity correlated with corneal refractive change and was predicted by the parabolic Munnerlyn equation (P<.0001).


CONCLUSIONS
After LASIK, AULCSF was not dependent on WFA, but mainly on patient age. WFA results correlated well with postoperative spherical equivalent refraction, asphericity, and Strehl ratio. These conclusions support a published hypothesis that postoperative low amount of WFA does not completely fit contrast sensitivity measurements.
Pop
Mihai
M
Cliniques Michel Pop, Montreal (Quebec) Canada. Mihaipop@cmpop.com
Payette
Yves
Y
D000328:Adult; D000368:Aged; D015350:Contrast Sensitivity / Q000502:physiology*; D003315:Cornea / Q000502:physiology*; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology* / Q000601:surgery*; D014792:Visual Acuity / Q000502:physiology