CONTACT LENS MATERIALS, DESIGN, AND CARE

The influence of contact lens materials and designs, including rigid and soft contact lenses in these aforementioned areas, has been of significant controversy in terms of their association or etiologic influence in CLD. Further, there also has been great interest in the role of contact lens care solutions, regimen practices in caring for contact lenses, and wearing schedule differences in terms of their influence on CLD.

The vast majority of today’s market is made up of soft contact lenses (~90%), while rigid lenses make up the remainder of the market. Of soft lenses used, silicone hydrogel lenses now make up the majority of the market share within most major worldwide markets. Through the years, there has been a question about the role of materials and designs on the problem of CLD. This issue was first recognized in the peer reviewed literature in the early 1970s for rigid lens materials and in the 1980s for soft lens materials. Since that time, practitioners and scientists have questioned the influence of polymer chemistry, and various other material attributes that can be measured and quantified. The attributes considered have included the bulk (e.g., water content, dehydration, ionicity, oxygen transmissibility, modulus, and mechanical factors) and the surface (e.g., friction, wettability, surface modification) of contact lens materials. To date, almost none of these attributes, with the possible exception of friction based on early evidence, appears to be associated directly with CLD. Studies evaluating these factors, however, can be difficult to draw conclusions from in that they are confounded with differing designs, lack of rigor, lack of consistent definitions (e.g., of discomfort), and an inability to hold the design constant when testing the influence of a material or its attribute. Lastly, contact lens material chemistry also is known to influence tear film component deposition (proteins and lipid primarily), but the role of deposition in general is equivocal, perhaps again due to difficulties and inconsistencies in measurement and quantification of deposition.

Contact lenses vary in terms of their designs, and there has been some notion that the design of a lens influences the on- eye comfort during wearing. There is no question that the design of contact lenses influences their ability to fit the ocular surface properly, and this is influential in terms of overall performance. For instance, for soft contact lenses, moderate on-eye movement (with tear exchange) and corneal coverage are recognized as being important, but its overall association with CLD is not entirely clear. Likewise, in rigid lens fitting, the influence of the eyelid–edge interaction is recognized as being important in terms of patient comfort, but this relation again is not entirely clear in terms of its overall association with CLD. However, there is even less consensus when considering the influence of various design attributes on CLD. That said, the size, shape, and contour of lens edges appear to be some of the most influential determinants of contact lens comfort for soft and rigid contact lenses.

Lastly, contact lens care solutions, contact lens care practices, and contact lens wear schedules certainly are of interest in terms of understanding their role(s) in CLD. To date, the peer-reviewed literature does not give a clear indication of specific formulations or components that may be associated either with increasing CLD or with improving contact lens comfort. However, most practioners agree that regular contact lens care by contact lens wearers, including rub, rinse, and adequate soaking (disinfection and cleaning) are important in the success of lens wear. Further, most agree that increasing the frequency of replacement of soft contact lenses is ideal for ocular health and potentially improving comfort, although it is difficult to define the ideal replacement schedule. To our knowledge, large-scale, well-controlled studies using contem- porary devices have not been conducted to provide insight into these issues.