Conjunctival and corneal pneumatic sensitivity is associated with signs and symptoms of ocular dryness.
Situ P, Simpson T, Fonn D, Jones LW.
Invest Ophthalmol Vis Sci. 2008 Apr 4 [Epub ahead of print]
Purpose: To investigate the relationships between dry eye symptoms, corneal and conjunctival sensitivity to pneumatic stimulation, tear film stability and clinical ocular surface characteristics in symptomatic and asymptomatic subjects.
Methods: 97 subjects were enrolled and grouped by a questionnaire based single score for symptom of ocular dryness (none to trace= "non-dry", mild to severe= "symptomatic"); 43 were symptomatic and 54 were non-dry. Corneal (K) and conjunctival (C) sensitivity were measured using a computer controlled Belmonte pneumatic (room temperature) stimulus. Symptoms were assessed using Ocular Surface Disease Index (OSDI). Ocular surface staining with fluorescein (FL) and Lissamine Green (LG), non-invasive tear film break-up time (NIBUT), and the Phenol Red Thread test (PRT) were assessed.
Results: The symptomatic group showed lower K and C thresholds (p0.01), greater corneal FL staining and conjunctival LG staining, and shorter NIBUT than the non-dry eye group (all others p0.05). OSDI scores were higher in the symptomatic group (p0.001). K and C thresholds, NIBUT were inversely correlated with OSDI scores and corneal and conjunctival staining (all p0.05). K and C threshold and NIBUT (all p0.01) were positively correlated. Stepwise multiple regression analysis showed that ocular surface sensitivity and NIBUT were significant predictors of OSDI scores.
Conclusion: Ocular irritation assessed using OSDI is associated with ocular surface hyperesthesia to cooling, corneal epitheliopathy and tear film instability. Although cause and effect are unclear, our analysis shows that altered corneal and conjunctival sensory processing and tear film attributes are essential aspects of what characterizes dry eye.