Contact Lens Wear and the Development of Squamous Metaplasia of the Surface Cells of the Conjunctiva

Abstract

To review the reported effects of contact lens wear on the surface epithelial cells of the human conjunctiva as assessed by conjunctival impression cytology (CIC). A literature search was undertaken to identify reports on the conjunctival health after contact lens wear, principally as assessed using CIC. Of 26 reports identified, 22 examined the bulbar conjunctiva, and 2 examined the tarsal conjunctiva. Just 16 reports provided data from which mean squamous metaplasia grades could be calculated, with the overall grade being just 0.7 on a 0 to 3 scale. Only 13 of these studies provided unambiguous data on the duration of contact lens wear, and only an apparent trend was evident in that grades of squamous metaplasia increased over early years of lens wear. Such a trend was not statistically significant either up to 6 years of average lens wear (P>0.05) or over all studies (P>0.5). The estimated variability in squamous metaplasia was substantially greater when low grades were reported, an observation that either reflects the heterogeneity in the cell response or highlights the difficulty in assigning low grades to cell samples. Based on subjective grading, CIC studies reveal no clearly definable relationship between the duration of contact lens wear and the extent of development of conjunctival squamous metaplasia. Logically, therefore, objective methods to assess squamous metaplasia are needed. Various options for quantitative CIC are discussed, including the use of in vivo confocal microscopy.