The effects of 24-h wear of various Dk-rigid gas-permeable (RGP) contact lenses on the rabbit corneal epithelium were studied by in vivo tandem scanning confocal microscopy (TSCM), and confirmed by scanning electron microscopy (SEM). Lenses used were polymethylmethacrylate (PMMA) (Dk/L = 0), RGP experimental A lens (siloxanylmethacrylate-fluoromethacrylate-methylmethacrylate , 33), experimental B (siloxanylmethacrylate-fluoromethacrylate, 56), and experimental C (siloxanylstyrene-fluoromethacrylate copolymer, 64 x 10(-9)) (cm/s) (ml O2/ml mm Hg) with 0.15-mm thickness (Dk/L measured by polarograph including boundary layer effect). After 24-h PMMA lens wear, TSCM showed no superficial epithelial cells but only exposed, underlying wing cells. The cornea with experimental A showed partial superficial epithelial desquamation. With experimental B wear, slight superficial epithelial cell swelling and desquamation were observed on the surface of the cornea. No changes were observed for the eye with experimental C and control. The observed severity of desquamation of superficial epithelial cells was dependent on the oxygen transmissibility (Dk/L) of RGP lenses worn. All in vivo findings were confirmed by SEM observations. Based on the results of this study, we conclude that (a) although Dk/L = 56 lens B shows no residual overnight corneal swelling, surface damage is still produced; (b) Dk/L = 64 lens C is best for epithelium showing the same corneal images as control; and (c) TSCM is a good way to evaluate the contact lens safety and efficacy in vivo at the cellular level noninvasively.