REDUCTION OF EVAPORATIVE TEAR WATER LOSS FROM THE OCULAR SURFACE BY MEANS OF A LIPID CONTAINING TEAR SUBSTITUTE

Abstract

Abstract: : Purpose: Prevention of evaporative water loss from the ocular surface could result in maintenance of a higher fluid volume over the ocular surface and reduction in the osmolarity shift typical of evaporative dry eyes. The aim of the study was to evaluate whether a lipid containing tear substitute could be of help in decreasing tear water evaporation loss in normal eyes, in the presence of artificially induced lipid layer inefficiency. Methods: By means of a "Stress Test Evaporimeter" (1) which allows evaluation of the resistance of tear film to evaporative stress in a reproducible controlled setting, the tear water evaporation of one eye of 16 normal subjects was studied in "normal" physiological conditions, after instillation of 0.4% oxybuprocaine chlorhydrate (a tensioactive anaesthetic commonly used in ophthalmology) and after instillation of oxybuprocaine chlorhydrate (6 minutes before) and a carbopol –trglycerid containing tear substitute (Lipovisc, Bausch & Lomb Oftal, Catania, Italy) (5 minutes before). The controlateral eye underwent the same procedure but received a carbopol tear substitute without the lipid compound. The differences in tear evaporation behaviour between the two eyes of each subject were measured and the difference of the means was statistically evaluated using Student’s t–Test. Results: The average Relative Humidity values after 1 minute were 1.23± 0.35 (S.D.) x10^–7gcm²/sec in normal conditions, 3.907± 0.7x10^–7gcm²/sec after 0.4% oxybuprocaine chlorhydrate, 3.22± 0.43x10^–7gcm²/sec after carbopol only tear substitute and 2.43±0.43x10^–7g cm²/sec (p<0.01) after carbopol–triglycerid containing tear substitute. Conclusions:Evaporative stress on tear film is a common feature of our way of life (air conditioning in the home, office, cars and planes, video work, windy or acid air environmental conditions, etc...). The instillation of a lipid containing carbopol–triglycerid tear substitute can significantly reduce evaporative tear water loss. Increased tear water evaporation, possibly the result of a defective tear lipid layer function, is a frequent feature in both evaporative and aqueous deficient dry eyes. A reduction in evaporative tear water loss could be of significant help for dry eye patients in whom an osmolarity shift is a characteristic feature and a possible source of chronic inflammation and epithelial damage. (1) Barabino S. et al. Adv Exp Med Biol 2002; 506:1153–7.

Keywords: cornea: tears/tear film/dry eye • clinical research methodology