Contact Lens Design & Materials

A Complex Relationship

By Neil Pence, OD, FAAO

There is increasing speculation that various lens materials or designs might be associated with an increased frequency of corneal infiltrates. It has also been discussed that the care system used, or lack of one in the case of daily disposable lenses, may play a role as well. Finally, some presentations have suggested that certain lens/lens solution combinations may demonstrate an increased risk for infiltrates (Kislan and Hom, 2010). This column will attempt to shed some light on the complexity of this issue.

Examining the Data

For demonstration purposes, let's suppose there are three contact lens designs (1, 2, 3), all in different materials, used in a particular practice or clinic. The patients who return for follow-up visits or subsequent annual visits also report using mainly three different disinfecting solutions (A, B, C).

Now let's find all the cases in which a contact lens patient has a recorded corneal inflammatory event at that practice or clinic over some particular time frame (one year, two years, etc.). The contact lens type and disinfecting solution is identified, and Table 1 shows the resultant number of cases of infiltrates.

Looking at the data, you might be concerned that a large number of the corneal infiltrative events involve Lens 1 and Solution A, far more than any other combination. As these events are taken very seriously by practitioners, it would seem normal to re-evaluate the use of this particular lens/solution combination. We might also feel obligated to share this data with other practitioners.

Consider the following factors: 60 percent of the lens patients in this practice wear Lens 1; 25 percent in this practice wear Lens 2; 10 percent of patients in this practice wear Lens 3; 60 percent of the patients in this practice use Solution A; 30 percent of the patients in this practice use Solution B; 10 percent of the patients in this practice use Solution C.

Now consider that every combination in our scenario has exactly equal likelihood of corneal infiltrative events. For a given number of patients and a given number of corneal inflammatory events/patient years of contact lens wear, the results in Table 1 show exactly what should be true simply based upon the percentages of use. If many patients wear one particular lens, and a large number uses one particular lens solution, the odds of a patient presenting with a corneal infiltrate and showing that particular lens/solution combination are much higher. Simply looking at the number of patients with infiltrates who use a particular lens/solution combination is not useful unless you know the percentages of use for both the lens and the disinfection solution.

It's Complicated

I do not know if there is an increased risk of corneal infiltrates with any contact lens/disinfection solution combination. The goal of this column is to provide a glimpse of how difficult it can be to answer this question. Add to that the difficulty in determining consistently just exactly what is or is not an inflammatory corneal event, the uncertainty of whether patients always report their solution accurately, etc., and we begin to appreciate how complicated it can be to arrive at an accurate answer. This is an important issue, and one we shall hope to explore further in future issues. CLS

For references, please visit www.clspectrum.com/references.asp and click on document #186.

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Dr. Pence serves as executive director, Clinical and Patient Services, Indiana University School of Optometry in Bloomington, Ind. He is a consultant or advisor to B+L, Ciba Vision, and Vistakon and has received research funding from AMO. You can reach him at pence@indiana.edu.