The Role of Damage Associated Molecular Patterns in Dry Eye Inflammation

Purpose: It has been shown that inflammation is an important part of dry eye disease (DED), which may lead to degradation of visual quality and the ocular surface. Toll-like receptors (TLR) have been shown to stimulate the production of dry eye associated inflammatory cytokines and matrix metalloproteinase (MMP). The purpose of this thesis was to determine if (1a) damage associated molecular patterns (DAMPs) which are thought to activate TLRs are increased on the ocular surface in dry eye subjects and to assess whether a low humidity environment (LHE) can modulate (1b) DAMP ocular surface levels (n=9 DED subjects) and (2) higher order aberrations (n=33 normal subjects).

Methods: Ocular surface disease index (OSDI), corneal and conjunctival staining, phenol red thread test (PRTT), osmolarity, sodium fluorescein tear break up time (TBUT), conjunctival erythemia, and/or meibomian gland expression were analyzed in each subject. The tear film (10-20µl) was collected and analyzed for HMGB-1 (ELISA) and HSP 27, 60, 70, 90 (Luminex Assay). Conjunctival impression cytology (CIC) samples were analyzed for cytokine and MMP mRNA or DAMP protein analysis. These data were collected under normal building temperature and humidity conditions (1) or following 2hr LHE (2a). To examine changes in visual performance, high and low contrast Log MAR visual acuity was measured and corneal topographies of the subject’s right eye were measured using the Nidek OPD Scan III and the Topcon KR-1W before and after 1hr LHE (2b).

Results: (1a) Thirty normal (n=15) or DED (n=15) subjects qualified for the study. In the DED subjects, there was a statistically significant increase in OSDI, TBUT, corneal staining and conjunctival staining (p ≤0.05). HMGB-1 was found to have significantly higher levels in the tear film of DED subjects compared to normals (p≤0.05) while there no difference in HSP-27, HSP-60, HSP-70, HSP-90α. In the CIC samples, there was no difference in HMGB-1, HSP-27, HSP-60 and HSP-90α, while HSP-70 levels were significantly decreased in DED subjects (1b). Following 2hr LHE, corneal staining was significantly increased and MMP-9 mRNA significantly upregulated in the conjunctiva by 2.4 ± 1.0 fold. There was no significant change in HMGB-1 or HSPs tear levels. There was no significant difference between visual acuity or third, fourth, and the third-sixth higher order aberrations using the KR-1W or the OPD-Scan III following LHE (2).

Conclusions: Dry eye subjects had higher levels of HMGB-1 in their tear film (1a) and LHE (2hrs) did not increase HMGB-1/HSPs levels despite additional corneal damage and increased MMP-9 mRNA expression in DED patients. (1b). LHE (1hr) did not increase HOA or alter visual acuity which may be a result of the short LHE duration (1hr vs 2hr) (2). These data suggest the DAMPs maybe involved in DED, but their ability to stimulate inflammation remains to be determined.