Mesopic contrast sensitivity function after laser in situ keratomileusis.

PURPOSE: To evaluate contrast sensitivity under mesopic conditions in patients who have undergone uncomplicated bilateral laser in situ keratomileusis (LASIK) for myopia. METHODS: Best-corrected monocular contrast sensitivity was measured with the Stereo Optical F.A.C.T. chart at 1.5, 3, 6, 12, and 18 c/deg in 20 patients (20 left eyes) before and after bilateral LASIK (with the Nidek EC-5000 excimer laser and the Automated Corneal Shaper). Mean preoperative refractive error was -6.40 ± 1.28 D (range -4.00 to -8.00 D) and postoperative mean refractive error was -0.41 ± 0.45 D (range -0.75 to +0.50 D). Contrast sensitivity function was measured before and 6 months after surgery using four different chart luminances: 85, 5, 2.5, and 0.1 cd/m 2 , the first being a photopic level and the rest mesopic. Log contrast sensitivity values at each spatial frequency were used for statistical analysis and normalized values for graphical representation. RESULTS: Contrast sensitivity of postoperative LASIK eyes did not differ from preoperative values at a photopic level (85 cd/m 2 ). However, under mesopic conditions (5 cd/m 2 or less) a statistically significant reduction (P .01 for 1.5, 3 and 6 c/deg). CONCLUSIONS: LASIK induced significant reductions in contrast sensitivity under mesopic conditions only at high spatial frequencies, even though the photopic contrast sensitivity function was normal.