Extended wear lens problems —Are they all eye wash?

Abstract

We have, the Croydon Eye Unit, always had a special interest not only in the development of modern cataract surgery but also the clinical and social management of the problems that arise immediately after operation. It was this interest which led us to be involved in the use of daily wear soft lenses for the aphakic patient in the early 70s (for example our work with Bausch & Lomb and the early Saufion 70). We soon became aware of the clinical and administrative difficulties of such lens systems. It was therefore a logical progression for us to become involved in the initial trials of extended wear lenses and these should have overcome many of the inherent problems of daily wear lenses. We were quite gratified with the results of these trials. Of the patients fitted at operation 84% were still happily wearing their lenses the end of the trial period. Following definitive fitting 78% of patients successfully completed the trial. When followed for a further two years 88% of the patients were still wearing their lenses. That is to say some of the patients had been using their lenses for between three and four years and a few patients had kept their lenses in for up to two years without a change! This was indeed encouraging but we were., by now, well aware of the two major problems which are probably linked and are associated with extended lens wear namely the red eye and the problem of deposition on the lens. We found an early stage in our work and have already reported that deposits and red eye syndrome accounted for about haft of the lenses that required to be replaced. Morgan (according to Kreiner) in Ontario, discussing the wearing of soft lenses in general, has estimated that deposits can cause 80% of the complications. Phillips, in his recent address to this Association, said that deposits were the greatest single complication of soft lenses and their rate was five times that of any other problem. That the problem remains still reflects on the materials and lens care systems that are currently available. Although the basic components of HEMA and PMMAare similar the HEMA material has a number of free hydroxyl groups which gives the material a high polarity and reactivity as well as a high water uptake, and the addition of PVP (Poly-vinyl-pyrrolidone) not only increases water uptake and oxygen permeability but also increases the material's reactivity. As a consequence these materials, so suitable for extended wear but of high polarity and reactivity, attract deposits and can indeed even incorporate them in their structure. Let us next consider the relationship of lenses of these materials to the tear film. Within the layered system of the tears are to be found proteins, lipids, mucins and inorganic substances and these can be adsorbed on to a soft lens lying within this environment. Also the lens causes changes to the physio-chemical status of the tear film which may favour the formation of precipitates. Attempts to resolve the problem of deposition on soft lenses have led to a plethora of solutions and cleaning regimes and systems, some of which can be summarized as follows: Cleaning Agents Actual ingredients in cleaning and soaking solutions