A main objective of disposing or regularly replacing contact lenses is to ensure that their performance remains optimal throughout their length of use. However, to date, visual performance has not been critically evaluated over the usual length of use for any of these lenses. Such a concern is particularly pertinent for Group IV lenses which are thought to produce a rapidly changing performance because of their ionic nature. The current study has critically measured the visual performance of two groups of 40 subjects, with LogMar VA charts of two contrasts (92% and 6%), under two luminance levels (250 and 2.5 cd/m(2)[superscript]) and by way of a subjective vision questionnaire. One group of subjects wore Group IV lenses, (Acuvue(TM)[trademark superscript]) on an extended wear basis for one week and the other group wore Group IV daily wear lenses (Sureview(TM)[trademark superscript) for two weeks. The results obtained revealed good visual satisfaction and visual performance which remained unchanged for both contact lens types, over the test periods. Conventional LogMar VA (high contrast, normal luminance) was -0.15 (20/15+) for both contact lens types and mean LogMar VA, for all test conditions, was +0.16 and +0.15 respectively, for the extended and daily wear modalities. Our conclusions are that, from the criteria of the visual performance, the replacement periods used are suitable recommendations for an unselected contact lens population. Study funded by Vistakon.