Corneal Stroma and Endothelial Cell Changes in Contact Lens Wearers Visualized with Confocal Microscopy

Abstract

Purpose: This study was designed to assess corneal microstructure (via confocal microscopy) and determine cellular changes related to clinical covariates during daily wear use of silicone hydrogel contact lenses

Methods: 218 patients were enrolled in the Daily Wear Corneal Infiltrative Event (DWCIE) Study and followed for up to 6 visits over 12 months. At the baseline and 5 month visits, a Nidek ConfoScan 4, 40X probe gel immersion exam was performed. Images were analyzed by experienced technicians. Total and anterior stromal reflectivity in the central and peripheral cornea were measured using Navis software. Immune cells at the sub-basal nerve plexus were counted manually. Endothelial cell density and morphology were analyzed by importing the confocal images into Konan Analysis software and using the Konan Center method. Covariates of interest included microbial bioburden on lenses, storage cases, lids and conjunctivae, tear break up time (TBUT), solution use, and corneal and conjunctival staining. Statistical analyses were performed with t-tests unless the data were not normally distributed, when non-parametric Wilcoxon tests were used.

Results: Immune Cells at the Sub-Basal Nerve Plexus: Patients with shorter TBUTs demonstrated a greater number of immune cells when compared to patients with longer TBUTs (p=0.03). Stromal Reflectivity: A decrease in lid microbial bioburden was associated with a decrease in peripheral total stromal reflectivity over 5 months (p=0.04). Endothelial Cell Density: Relative to baseline, cell density was higher at 5 months in patients with substantial microbial bioburden on lenses (p=0.03).

Conclusions: Short TBUT was associated with a greater number of corneal immune cells which may represent the known immunological response related to dry eye disease and/or higher tear osmolarity. Peripheral stromal reflectivity was decreased when lid bioburden was decreased, suggesting that peripheral stromal cellular infiltration and/or subclinical inflammatory responses are influenced by the presence of microbes. The latter theory is consistent with the association recently reported from the DWCIE study between abnormal lid bioburden and the development of contact lens related corneal inflammatory events.

Keywords: 477 contact lens • 596 microscopy: confocal/tunneling • 484 cornea: stroma and keratocytes