Extended wear of contact lenses has led to a significant increase in serious complications, including infections and corneal ulcerations. Many practitioners suspect that poor cleaning and handling of the lenses at the time of their relatively infrequent removal may be a major factor in these problems. To date, virtually all extended-wear lenses have been soft hydrogels, inherently hydrophilic in nature. Recently, the first rigid gas- permeable (RGP) lens was approved for extended wear; many will follow. Although such lenses can have high oxygen permeability, rivaling or exceeding soft materials, and possess many of the advantages of the old, hard, PMMA lenses, they have hydrophobic surfaces, and wetting characteristics can be crucial to their successful wear. Even in daily wear, a common problem is 3- and 9-o'clock fluorescein staining of the epithelium, thought to be due to excessive drying of the corneal surface in these areas. We will examine the detailed wetting performance (in terms of tear film thickness distribution and breakup time) and coating and deposit buildup on in vivo RGP contact lens surfaces. In particular, we will examine the effects of 4 major variables on wettability and deposit severity: lens type (low, high, and super- high oxygen permeable); cleaning regimen (standard, and a more rigorous technique using thorough wiping with a cleaner-soaked cotton swab); type of patient (normals, and marginal dry-eyed); and wearing regimen (daily and extended wear). The methods depend upon the use of a recently developed specular reflectometer-interferometer assembled by the Principal Investigator. Preliminary studies have proven the unique capabilities of this new instrument to reveal in vivo wetting factors that determine the interactions of contact lenses with the tear fluid, lids, and cornea. A key procedure will be determination of prelens tear film thickness distribution and the manner and time course of its thinning and breakup during interblink periods. Concurrently, an ordinal system of lens deposit grading will allow correlation between the two factors. Over 300 lenses will be worn for 10-month periods, involving 4 scheduled examinations per lens.
