Alterations in Corneal Nerve Fiber Density and Pain Markers during the Progression of Desiccating Stress-Induced Dry Eye Disease

Abstract

Purpose: : Pain is a major symptom of patients suffering from chronic Dry Eye disease. To begin to understand if the immunopathogenesis of desiccating stress (DS)-induced Dry Eye is associated with a pain response, corneal nerve fibers and expression of putative pain markers were evaluated over the course of disease.

Methods: : Dry Eye disease was induced by exposing female C57BL/6 mice to desiccating stress (DS: subcutaneous scopolamine (0.5 mg/0.2ml) TID; humidity <40%; sustained airflow). Ocular surface and central nervous system (CNS) tissues were collected for analysis at various time points. Immunohistochemistry was used to evaluate changes in corneal nerve fiber density and to quantify expression of putative pain markers (e.g. c-Fos, pERK, EGR1) within the CNS at 0, 5, 10, 15, and 20 days of DS.

Results: : Immunohistochemistry on flat mount whole corneas revealed alterations in corneal nerve fiber density in mice with Dry Eye disease. For example, the density of TRPM8 nerve fibers decreased 46% in Dry Eye mice relative to naïve control mice. In addition, the progression of Dry Eye disease was associated with coordinate expression of c-Fos within the CNS. By 15 days of DS the average number of c-Fos+ cells was significantly (p=0.0001) increased in the cerebral cortex (36.1±6.0%) compared to controls (10.9±1.0%). A similar trend was observed in the ventral striatum and hypothalamus of Dry Eye mice at 15 days DS (43.1±3.6% versus 13.8±2.7%; p=0.000001).

Conclusions: : These data suggest that mice develop corneal nerve degeneration and pain during the immunopathogenesis of DS-induced Dry Eye disease.

Keywords: cornea: tears/tear film/dry eye • inflammation • nerve fiber layer