Characterization of Keratoconjunctivitis Sicca in the Rat Model

Abstract

Purpose: : Keratoconjunctivitis Sicca (KCS) results in decreased tear production and irritation of the anterior segment. An animal model is necessary for understanding the pathophysiology of the disease and for developing new therapy. Furthermore, an extended study of the dry eye model is necessary to observe the chronic effects of the disease.

Methods: : A rat model for dry eye was developed through denervation of the trigeminal nerve by a reliable and reproducible method. A radiofrequency probe was inserted ventrally to thermally ablate the V1-V2 junction using stereotaxic surgery. Corneal sensation was tested and tear production was measured in each eye prior to surgery and on the tenth, fifteenth, and twentieth day after surgery using phenol red tear threads.

Results: : All animals were treated with radiofrequency ablation and lost corneal sensation.The experimental eye showed significantly less tear production compared to the control eye. Prior to trigeminal denervation, baseline tear production in both eyes were similar (6.3 ± 1.4 mm vs 6.6 ± 1.2 mm, p=.42, n=33). However, tear production in the treated left eye was 29% less than the control eye on the 10^th postoperative day (4.7 ± 1.8 mm vs. 6.6 ± 1.8 mm, P<0.01, n=33), 60% on the 15^th postoperative day (3.1 ± 0.6 mm vs. 7.7 ± 0.7 mm, p <0.01, n=9), and 36% on the 20^th postoperative day (4.7 ± 1.2 mm vs. 7.4 ± 1.3 mm, p <0.01, n=9). Postoperative day 10 showed that tear production in the treated left eye decreased by 25% compared to preoperative values (4.7 ± 1.8 mm vs. 6.3 ± 1.4 mm, P<0.01, n=33), by 51% on the 15^th day (3.1 ± 0.6 mm vs. 6.3 ± 1.4 mm, p <0.01, n=9), and by 25% on the 20^th day (4.7 ± 1.2 mm vs. 6.3 ± 1.4 mm, p <0.01, n=9). The control eyes showed no significant difference in tear production compared to baseline. Significant decrease in tear production in the treated eye compared to the control eye was determined by an unpaired student’s T-test assuming unequal variance. Prior histopathologic data of the conjunctiva and the cornea after radiofrequency trigeminal nerve ablation revealed decreased tear-producing goblet cells in the conjunctiva and the presence of inflammatory cells beneath the cornea epithelium.

Keywords: cornea: tears/tear film/dry eye