The effects of experimental tear film removal on corneal surface regularity and barrier function

Purpose: To evaluate corneal surface regularity and asymmetry, corneal thic kness, barrier function, and contrast sensitivity after experimental remova l of the precorneal tear layer. Design: Prospective, clinic-based, nonrandomized (self-controlled) comparat ive trial. Participants: Six eyes of six healthy volunteers (three males, three female s; age range, 29-40 years). Methods: A precorneal tear lesion was created by pressing a sterile Biopore (Millipore, Bedford, MA) Teflon membrane against the central cornea. Corne al topography with both the Topographic Modeling System (TMS-1; Computed An atomy, Tomey Technology, Cambridge, MA) and the Orbscan (Orbscan Inc., Salt Lake City, UT) were performed before the lesion was created and 30 seconds , 1 hour, and 4 hours after the lesion was created. Surface regularity and surface asymmetry indices were evaluated by the TMS-1 topography system. Ma ximum and minimum keratometric readings, corneal fluorescein staining, cont rast sensitivity, and corneal thickness were evaluated before and after the tear lesion. Cytologic membranes were stained for MUC4 mucin using an indi rect immunofluorescent staining technique. Confocal microscopy was performe d to evaluate the integrity of the corneal epithelium in two eyes. Analysis of variance with polynomial contrasts was used to examine time trends of t he outcome variables. Main Outcome Measures: The change in corneal surface regularity and asymmet ry indices, corneal thickness, permeability to fluorescein dye, and contras t sensitivity before and after the lesion was made were compared. Results: The corneal epithelium in the area of the lesion showed intense fl uorescein staining 30 seconds postlesion but appeared normal by 4 hours. Co nfluent, homogeneous staining for MUC4 mucin was observed on the membranes used to create the lesion in all cases. The surface regularity index measur ed with the TMS-1 increased after the lesion was created and decreased towa rd normal by 4 hours (P = 0.017). Corneal thickness measured by the Orbscan instrument significantly increased in the central (P = 0.001), superior (P = 0.006), inferotemporal (P < 0.001) and superotemporal (P = 0.001) cornea immediately following the lesion and returned to normal by 4 hours. The le sion caused a decrease in visual acuity at 6.30%, 4% and 2.5% contrast sens itivities 1 hour postlesion and these measurements returned to prelesion va lues by 4 hours (P = 0.085, P = 0.005, P = 0.043). Conclusions: The precorneal tear layer serves as a permeability barrier and is essential for maintaining a smooth quality optical surface. Ophthalmolo gy 2000;107:1754-1760 (C) 2000 by the American Academy of Ophthalmology.