 Interested subjects who meet the entry criteria for the study will be scheduled for four sessions of approximately 30 minutes duration each. Informed consent obtained. Baseline measurements of visual acuity and corneal and conjunctival physiology will be recorded. An examination of the endothelium of the corneas will be conducted using the specular microscope, readings obtained at 5 locations on each cornea: one in the centre and one in each of the superior, inferior, nasal and temporal peripheral regions, approximately 2mm from the limbal margin. The assigned lenses will be inserted according to a fixed-allocation randomization schedule, where each session follows an optimized 2- period simultaneous crossover design, which specifies lenses to be used in each of the four sessions. Lenses will be worn for 20 minutes and then removed. Endothelial specular microscopy will be conducted at 20 minutes with the lenses on. A final evaluation of corneal and conjunctival physiology will be performed prior to subject clearance from the study. 