The effect of modification procedures on rigid gas permeable contact lenses: the UM-St. Louis Study

The purpose of this study is to evaluate the effect of frequently performed modification procedures on quality of vision, surface wettability, optical quality and subjective response. One subject was optimally fitted with both silicone/acrylate (S/A) and fluoro-silicone/acrylate (F-S/A) lens materials of identical design. Two methods of surface polishing, edge polishing and repowering were used in addition to three different spindle speeds. Each pair of lenses was worn by the subject for a period of 4 hours and the subjective response was then compared to the baseline or premodification data. In addition, both low magnification photography and Scanning Electron Microscopy (S.E.M.) were performed on each lens. The results showed that the addition of 0.50D minus power reduced visual acuity, contrast sensitivity function and optical quality with one of the methods used. Front surface polish and edge polish procedures did not appear to affect short-term performance. Controlling polish, application and tool pressure on certain procedures resulted in similar findings. Further studies would be beneficial to evaluate the effect of longer wearing periods and the use of other modification procedures. The authors conclude that S/A and F-S/A lens materials can be successfully modified in-office with adherence to recommended guidelines.