In vivo confocal microscopy: Increased conjunctival or episcleral leukocyte adhesion in patients who wear contact lenses with lower oxygen permeability (D_k) values

Purpose: Contact lens wear is known to threaten the health of the ocular surface. In vivo confocal microscopy (IVCM) to visualize leukocyte rolling and extravasation in inflammation was recently described. We tested the hypothesis that contact lens wear is associated with measurable inflammation in superficial vessels. Methods: Leukocyte rolling and sticking (hallmarks of the inflammatory process) were recorded by IVCM. IVCM was performed on conjunctival or episcleral blood vessels bilaterally on 55 contact lens wearers (15 male, 40 female) and 22 non-contact lens wearers (8 male, 14 female). Data were analyzed in 2 ways. Considering each vessel as an independent variable resulted in 132 analyzable vessel segments (13 daily disposable contact lenses, 67 traditional contact lenses, 14 rigid gas-permeable lenses, and 38 controls). Considering each subject as an independent variable resulted in analyzable data for 47 subjects (5 daily disposable contact lens wearers, 22 traditional contact lens wearers, 5 rigid contact lens wearers, and 15 control patients). Free-flowing, sticking, and rolling cells were counted in the vessels. Multiple parameters including mean flow velocity, shear rate, rolling cells/mm²/min, and sticking cells/mm² were calculated. Results: We found no significant difference in leukocyte adhesion between control patients and patients wearing daily disposable, traditional disposable, or rigid gas-permeable lenses in both types of statistical analyses. However, the data regarding vessel segments as an independent variable show that there were more rolling cells in patients who wore contact lenses with oxygen permeability values (D_k) less than 10 as compared to those who wore contact lenses with oxygen permeability values greater than 16 (P < 0.01) or compared to controls (P < 0.01). Conclusion: IVCM is a novel, powerful technique to recognize a critical but subclinical component of inflammation. Although our data indicate that contact lens wear does not markedly increase rolling and sticking of leukocytes in conjunctival or episcleral vessels, there may be subclinical inflammation in association with lenses with the lowest oxygen permeability.