Twelve patients wore J&J "Acuvue" lenses for two weeks and Bausch & Lomb "SeeQuence" lenses for four weeks on a daily-wear basis, whilst using a chlorine release care system with the Acuvue lenses and a chlorhexidine-based tablet system with the SeeQuence lenses. Prior surfactant cleaning was undertaken with each system. High contrast visual acuity levels were higher with the Acuvue lenses at both initial (p=0.05) and final visits (p>0.02), whilst low contrast acuity was no different initially (p=NS), but higher with the Acuvue lens on the final visit (p=0.01). Whilst the acuity with the Acuvue lens remained constant during the period of the trial, visual acuity was seen to reduce with time with the SeeQuence lenses. Visual quality, comfort, handling performance, simplicity of the care regimen and overall satisfaction was assessed. In all aspects except the care regimen (p=NS), Acuvue lenses were judged to be superior (p>0.03). Whilst in-vivo slit-lamp microscopy revealed no statistically significant difference in the degree of deposition, independent laboratory-based assays of lipid and protein revealed that the Acuvue lenses exhibited greater amounts of protein deposition (p>0.0005) and that SeeQuence had increased levels of lipoidal spoilation (p=0.01). Correlation between the measured reductions in visual acuity and the measured deposits indicate that it is primarily protein which causes the reduction in acuity seen with the Acuvue lens (p=0.02), which can best be detected with low contrast charts, and that lipid is primarily responsible for reducing acuity with SeeQuence lenses (p>0.02), which can be detected with both high and low contrast charts.Slit-lamp examination indicated that conjunctival staining was significantly greater with the Acuvue lenses (p>0.04). Study funded by Bausch and Lomb.