It is the long-term objective of the study to investigate the basic biophysical nature of the human tear film, to examine the effects of the presence of a contact lens upon this fluid layer, and determine correlations between these effects and the physiological consequences to the anterior segment of the eye.More specifically, the study will determine the interactions of the in vivo tear fluid with hydrogel contact lenses and correlate this interaction with the wetting performance, in-eye desiccation, rate and type of lens surface deposits and problems associated with lens wear. This knowledge will aid in understanding the underlying reasons why such complications occur.Over four million people in the U.S. use extended-wear soft contact lenses,and over nine million use daily-wear soft contact lenses. Many eye-care practitioners believe, largely based upon their personal experience, that such complications as giant papillary conjunctivitis (GPC), infection, corneal ulceration, etc., are more prominent with this type of lens than with the rigid gas permeable materials. The less frequent cleaning of the extended-wear lenses results in a higher level of contamination of the lens surface on average at any given point in the lens-wearing/cleaning cycle (after the first day) than with daily wear lenses compromising the stability of the tear film. Once this reaches the point where breakup times consistently fall below the average length of interblink periods, debris and contaminated lipid an mucous from the tear fluid and lid margins are left behind on a dry lens surface. This leads to irritation of the lids and accelerated generation of cellular debris in the tear fluid, further adversely affecting the tear film stability. Thus, a progress of self-perpetuating events can occur which lead to an increasingly unstable tear film, notable discomfort, and the potential for serous infection. In this study, two types of daily wear soft contact lenses will be compared with two types of disposable lenses worn on both a daily-wear (with two-week replacement) and extended-wear (with one-week replacement) basis. The same patients will use all lens types and wearing modalities.It will be determined how the factors of lens type (daily-wear only vs. disposable), cleaning/disinfection (for daily wear), and wearing conditions (daily vs. extended wear) affect the in vivo interactions between the tear fluid and the lens surfaces and the physiological response of the eye and lids to that wear. This response will be monitored in terms of change sin the surface wetting of the lenses, their in-eye desiccation, the buildup of deposits and coatings on the lenses, and any other problems of the anterior segment which occur. The key feature of the methodology is the use of the tear film interferometer developed by the Principal Investigator. Its use has been notably successful and effective in allowing the actual visualization of the in vivo tear film and its interactions with contact lens surfaces.
