Assessment Methods and Causes of Eye Irritation in Humans in Indoor Environment

Abstract

No model is well established for indoor air induced eye irritation — a consequence of the lack of good models for the common chemical sense in general and even more a consequence of the extreme lack of data. We have to use the understanding from models established in other situations or related to other organs. Existing models suggest that indoor air pollutants may decrease the stability of the tear film either by changing the surface lipid layer or by decreasing the amount of mucus in the water-phase of the film. This may then lead to increased dryness and subsequently damage the corneal and conjunctival epithelium. This may by itself or by increasing sensitivity of the nociceptors in the epithelium lead to increased sensory irritation. Furthermore, inflammatory responses may follow due to release of eg. neuropeptides from the nociceptors. Another mechanism suggested is that inflammatory responses leads to release of mediators triggering nociceptors (histamine release is an example). Reports (epidemiological and and experimental) support that dust and volatile organic substances (VOCs) may induce decreased tear film stability, increased epithelial damage, increased inflammatory responses as well as sensory irritation. Furthermore, there seem to be some association between objective parameters and subjective irritation for Polymorphonuclear neutrophils and tear film stability. This is remarkable results, achieved within the past 5 years. However, data is not sufficient to decide about the reliability of pathophysiological relations suggested in the models. The main future need is to gather more data on these methods and further development and refinement of measurement techniques.