Estimation of Osmolarity within Areas of Tear Breakup

Title Estimation of Osmolarity within Areas of Tear Breakup
Author, Co-Author Jun Zhang, Carolyn Begley, Richard Braun, Ping Situ
Program Number
Indiana University School of Optometry
Abstract Purpose:  Previous studies showed that tear breakup (TBU) was associated discomfort (Varikooty et al, 2009; Begley, 2013) and that increased hyperosmolarity within areas of TBU may be a factor in causing the discomfort (Liu, 2010).  The purpose of this study was to estimate tear film osmolarity by fluorescence intensity within areas of TBU using the pain response as a reference.

Methods: The tear film fluorescence of 10 subjects was monitored during blink suppression while subjects turned a “pain knob” (0-10 scale) to indicate discomfort level. The percent changes in pixel intensity (PI) within the leading areas of TBU were analyzed by custom MATLAB programs. Due to the uncertainty of the initial fluorescein concentration, tear film osmolarity within TBU was estimated by percent tear thinning using both PI and square root of PI (Nichols, 2012) versus the pain response as a reference (Liu, 2010).

Results: TBU ranged from 0.41% to 76.4% of the corneal area, with an average of 13.0%±17.0%. The range and average slope of the pain knob, the TBU% area and the %PI was 0.9-2.9/sec (average of 1.5±0.6sec), 0.01 to 7.86%/sec (average of 2.81±2.41), 2.87-18.35% (average of 7.41±4.87), respectively. Tear film osmolarity estimates within TBU ranged from 400-500mOsm/Kg at pain level 4, 450-600mOsm/Kg at level 6, 500-900mOsm/kg at level 8 and 600-1000mOsm/Kg at level 10, depending on whether PI or square root of the PI was used to determine thinning. The range of estimated osmolarity within TBU at the end of trials was 392-2500 mOsm/Kg using PI and 343-866 mOsm/Kg using the square root of the PI.

Conclusion:  This method uses fluorescence intensity and the pain response to estimate increases in the level of hyperosmolarity within areas of TBU. More accurate estimates could include other factors, such as local fluid flow, osmosis and diffusion (Braun 2014).
Affiliation of Co-Authors Indiana University, School of Optometry, Department of Mathematical Sciences,University of Delaware, Indiana University, School of Optometry