Assessment of stromal keratocytes and tear film inflammatory mediators during extended wear of contact lenses

Purpose: To monitor quantitative changes in stromal keratocyte density and the level of tear film inflammatory mediators following extended contact lens wear. Methods: Twenty-two subjects aged 32 +/- 11 years participated in this cross-sectional study. Eleven subjects had worn silicone hydrogel (Si-H) lenses on a 30-day continuous wear basis for 12 months. Eleven subjects had worn rigid gas permeable lenses on the same basis for 12 months. Eleven age-matched control subjects were also recruited. Ultrasound pachometry, confocal microscopy, and tear fluid sample collection were performed on all subjects. Tear samples were assayed for epidermal growth factor (EGF), hepatocyte growth factor (HGF) and interleukin (IL)-8. Results: Corneal thickness was similar for all subject groups. Total keratocyte density was not different between the 3 groups; however, keratocyte density was lower for rigid lens wearers in the anterior to mid stroma and lower for Si-H lens wearers in the posterior stroma compared with control subjects. Rigid lens wearers exhibited an irregular keratocyte distribution across the corneal stroma. EGF concentration and rate of release was greater in the tears collected from the rigid lens wearers and Si-H lens wearers, and IL-8 concentration was higher in the samples collected from the rigid lens wearers compared with the samples collected from the control subjects. Conclusions: Mechanical stimulation of the corneal surface due to the physical presence of a contact lens and the consequent release of inflammatory mediators may account for a loss or redistribution of keratocytes.