Life expectancy of rigid gas permeable and high water content contact lenses.
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PURPOSE: The purpose of this study was to evaluate the life expectancy of various rigid gas permeable (RGP) lens materials used on a daily wear basis and to compare these results with the life expectancy of a matched group of soft lens wearers. METHODS: We retrospectively analyzed the records of 600 contact lens wearing patients (300 soft contact lens users and 300 RGP lens users fit between September 1987 and September 1994. None of the subjects wore lenses on a planned replacement system. For the purpose of the study, RGP lenses were divided into three groups: < or = 40 Dk were considered low-Dk; 41-89 Dk were considered mid-Dk; and > or = 90 Dk were considered high-Dk. All soft lenses were high water content lenses (> or = 60% water content). Lenses were included if they were replaced due to loss, breakage, deposition, or poor wettability but not if replaced because of changes in fit or prescription. RESULTS: The mean (+/- SD) life-spans of each lens type in months were 19.9 +/- 17 for low-Dk RGP lenses, 15.9 +/- 13.3 for mid-Dk RGP lenses, 9.0 +/- 8.2 for high-Dk RGP lenses, and 6.4 +/- 5.2 for high water content soft lenses. Statistical analysis using a one-way ANOVA on ranks indicated that these results were statistically significant (P < 0.0001). CONCLUSIONS: Patients should be informed that high-Dk lenses (RGP and soft) provide substantial clinical benefits and that they should except to replace high-Dk RGP lenses after approximately 6 months. This lends further credence to the use of high-Dk lenses on a planned replacement basis.
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