title: Effectiveness of dry eye therapy under conditions of environmental stress.
abstract: OBJECTIVE
  Dry eye is often characterized by increased tear evaporation due to poor tear film quality, especially of the lipid component of the tear film. Using an environmental chamber to induce environmental stress, this study compared the effect of three lubricant eye drops on various aspects of tear physiology in a crossover design (evaporation was the principal outcome measure).
  
  
  METHODS
  Three eye drop formulas were tested: 0.5% carmellose sodium (Drop C), 0.5% carmellose sodium with added lipid (Drop C-L) and 1.0% glycerine with added lipid (Drop G-L). Nineteen control and 18 dry eye subjects used each product for 2 weeks, three times per day, in a random order, with a minimum 1-week washout between treatment periods. Tear evaporation, break up time, osmolarity, tear structure (by interferometry) and patient symptoms were assessed with the subjects adapted for 10 min in an environmental chamber controlled at 20% relative humidity and 22 °C. The treatment effects were analyzed using general linear model repeated measures analyses of variance.
  
  
  RESULTS
  In dry eye subjects, evaporation, break up time, osmolarity and symptoms improved for all formulas (p < 0.05). Normal subjects showed some improvements: evaporation with C-L, osmolarity with C and symptoms with C-L and G-L. Change in evaporation was greater for both C-L and G-L versus C (p < 0.05), and there was a trend for C-L to reduce evaporation more than G-L (p < 0.11). There were no significant treatment effects on tear film structure.
  
  
  CONCLUSIONS
  Overall, the eye drop formula containing both carmellose sodium and lipid (C-L) produced a greater treatment effect on tear evaporation than the other formulations containing only one of these ingredients. This study also demonstrates the utility of a controlled environmental chamber in showing the difference in performance between dry eye treatments.
authors.affiliation: Vision Sciences, Glasgow Caledonian University, Glasgow, UK. a.tomlinson@gcu.ac.uk
authors.forename: Alan
authors.initials: A
authors.lastname: Tomlinson
authors.forename: Louise C
authors.initials: LC
authors.lastname: Madden
authors.forename: Peter A
authors.initials: PA
authors.lastname: Simmons
mesh_terms: D002266:Carboxymethylcellulose Sodium / Q000008:administration & dosage; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004337:Drug Carriers / Q000008:administration & dosage; D015352:Dry Eye Syndromes / Q000188:drug therapy* / Q000378:metabolism; D004781:Environmental Exposure; D005990:Glycerol / Q000008:administration & dosage; D006801:Humans; D006813:Humidity; D007368:Interferometry; D009883:Ophthalmic Solutions / Q000008:administration & dosage*; D017060:Patient Satisfaction; D013312:Stress, Physiological; D013666:Tears / Q000378:metabolism; D016896:Treatment Outcome
chemical_list: D004337:Drug Carriers; D009883:Ophthalmic Solutions; D002266:Carboxymethylcellulose Sodium; D005990:Glycerol