title: Validating a new device for measuring tear evaporation rates.
abstract: OBJECTIVE
  To calibrate and validate a commercially available dermatology instrument to measure tear evaporation rate of contact lens wearers.
  
  
  METHODS
  A dermatology instrument was modified by attaching a swim goggle cup such that the cup sealed around the eye socket. Results for the unmodified instrument are dependent on probe area and enclosed volume. Calibration curves were established using a model eye, to account for individual variations in chamber volume and exposed area. Fifteen participants were recruited and the study included a contact lens wear and a no contact lens wear stage. Day and diurnal variation of the measurements were assessed by taking the measurement three times a day over 2 days. The coefficient of repeatability of the measurement was calculated and a linear mixed model assessed the influence of humidity, temperature, contact lens wear, day and diurnal variations on tear evaporation rate. The associations between variables were assessed using Pearson correlation coefficient.
  
  
  RESULTS
  Absolute evaporation rates with and without contact lens wear were calculated based on the new calibration. The measurements were most repeatable during the evening with no lens wear (COR = 49 g m⁻² h) and least repeatable during the evening with contact lens wear (COR = 93 g m⁻² h). Humidity (p = 0.007), and contact lens wear (p < 0.01), significantly affected the tear evaporation rate. However, temperature (p = 0.54) diurnal variation (p = 0.85) and different days (p = 0.65) had no significant effect after controlling for humidity.
  
  
  CONCLUSIONS
  Tear evaporation rates can be measured using a modified dermatology instrument. Measurements were higher and more variable with lens wear consistent with previous literature. Control of environmental conditions is important as a higher humidity results in a reduced evaporation rate.
authors.affiliation: Brien Holden Vision Institute, Sydney, Australia; School of Optometry and Vision Science, University of New South Wales, Sydney, Australia.
authors.forename: Athira
authors.initials: A
authors.lastname: Rohit
authors.forename: Klaus
authors.initials: K
authors.lastname: Ehrmann
authors.forename: Thomas
authors.initials: T
authors.lastname: Naduvilath
authors.forename: Mark
authors.initials: M
authors.lastname: Willcox
authors.forename: Fiona
authors.initials: F
authors.lastname: Stapleton
mesh_terms: D000328:Adult; D002138:Calibration; D003261:Contact Lenses / Q000009:adverse effects; D003880:Dermatology / Q000295:instrumentation; D003941:Diagnostic Techniques, Ophthalmological / Q000295:instrumentation*; D015352:Dry Eye Syndromes / Q000175:diagnosis*; D004867:Equipment Design; D005260:Female; D006801:Humans; D008297:Male; D015203:Reproducibility of Results; D013666:Tears / Q000737:chemistry*; D014835:Volatilization; D055815:Young Adult
keywords: contact lens; lipid layer; tear evaporation; tear film; validation