title: Quantitative analysis of tear film fluorescence and discomfort during tear film instability and thinning.
abstract: OBJECTIVE
  The purpose of this study was to test the association between tear film fluorescence changes during tear break-up (TBU) or thinning and the concurrent ocular sensory response.
  
  
  METHODS
  Sixteen subjects kept one eye open as long as possible (MBI), indicated their discomfort level continuously, and rated ocular sensations of irritation, stinging, burning, pricking, and cooling using visual analog scales (VAS). Fluorescence of the tear film was quantified by a pixel-based analysis of the median pixel intensity (PI), TBU, and percentage of dark pixels (DarkPix) over time. A cutoff of 5% TBU was used to divide subjects into either break-up (BU) or minimal break-up (BUmin) groups.
  
  
  RESULTS
  Tear film fluorescence decreased (median PI) and the percentage of TBU and DarkPix increased in all trials, with the rate significantly greater in the BU than the BUmin group (Mann-Whitney U test, P < 0.05). The rate of increasing discomfort during trials was highly correlated with the rate of decrease in median PI and developing TBU (Spearman's, r ≥ 0.70). Significant correlations were found between corneal fluorescence, MBI, and sensory measures.
  
  
  CONCLUSIONS
  Concentration quenching of fluorescein dye with tear film thinning best explains decreasing tear film fluorescence during trials. This was highly correlated with increasing ocular discomfort, suggesting that both tear film thinning and TBU stimulate underlying corneal nerves, although TBU produced more rapid stimulation. Slow increases in tear film hyperosmolarity may cause the gradual increase in discomfort during slow tear film thinning, whereas the sharp increases in discomfort during TBU suggest a more complex stimulus.
authors.affiliation: Indiana University School of Optometry, Bloomington, Indiana 47405, USA. cbegley@indiana.edu
authors.forename: Carolyn
authors.initials: C
authors.lastname: Begley
authors.forename: Trefford
authors.initials: T
authors.lastname: Simpson
authors.forename: Haixia
authors.initials: H
authors.lastname: Liu
authors.forename: Eliza
authors.initials: E
authors.lastname: Salvo
authors.forename: Ziwei
authors.initials: Z
authors.lastname: Wu
authors.forename: Arthur
authors.initials: A
authors.lastname: Bradley
authors.forename: Ping
authors.initials: P
authors.lastname: Situ
mesh_terms: D000328:Adult; D001767:Blinking / Q000502:physiology*; D003315:Cornea / Q000378:metabolism* / Q000503:physiopathology; D015352:Dry Eye Syndromes / Q000175:diagnosis / Q000378:metabolism / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D013666:Tears / Q000378:metabolism*; D055815:Young Adult