To evaluate the relationship between contrast sensitivity, surgical treatment zone, and clearance (ablation or clear zone — pupil diameter), photorefractive keraectomy (PRK) and radial keratotomy (RK).
Saint Louis University Eye Institute St. Louis, Missouri, and Hunkeler EyeCenter, Kansas City, Missouri, USA.
Thirteen patients had PRK and 20, RK. Contrast sensitivity was measured with the Stereo Optical F.A.C.T. (F.A.C.T.) and VectorVision CSV 1000 (V.V) charts Pupils were measured with the Rosenbaum card.
In the PRK group, W contrast sensitivity at 6 and 12 cycles per degree(cpd) correlated withthe ablation zone (r2 = 0 18 and 0.22, respectively) while visual acuity and F.A.CT. contrast sensitivity did not correlate. In the RK group both W and F.A.C.T. contrast sensitivity contrast sensitivity at 6 cpd correlated with clearance (r2 = 0.29 and 0.12, respectively). Pupils were larger with the W test than with the F.A.C.T. chart because ambient chart luminance was less in the former
Contrast sensitivity is likely a more sensitive indicator of visual function than acuity in refractive surgery. The W system unmasks aberrations, from the transition zone of ablated and unablated cornea in PRK; Larger samples are needed to determine the critical ablation clearance of the pupil to avoid loss of visual function.