A Novel Method of Measuring Tear Evaporation Rates using Infrared Thermography
Andrea Petznick1,
Samantha Sze Yee Lee1, Jen Hong Tan2, U. Rajendra Acharya2,3,4,
Eddie Ng5, Louis Tong1,6,7,8
1Singapore
Eye Research Institute, Singapore
2School
of Engineering, Ngee Ann Polytechnic, Singapore
3SIM
University, Singapore
4Singapore Institute of
Technology – University of Glasgow, Singapore
5School of Mechanical and Aerospace Engineering,
Nanyang
Technological University, Singapore
6National
Eye Centre, Singapore
7Duke-NUS
Graduate Medical School, Singapore
8Yoon
Loo Lin School of Medicine, National University of Singapore
PURPOSE: Dry eye is a very
common medical problem and meibomian gland dysfunction (MGD) may be an
aggravating factor. There is no single reliable diagnostic tool to determine
the presence and severity of dry eye and MGD. The measurement of dynamic tear
evaporation rates would allow for a more objective diagnosis. In this study, we
present a novel non-invasive method of measuring tear evaporation rates using
infrared thermography that is reliable and able to detect changes after heat
therapy.
METHODS: Infrared thermographic sequential images of ocular surface temperature were recorded
from healthy participants
(mean age ± SD: 24±7 years) while remaining in a consulting room with a
temperature of 22.08±0.77°C and humidity of 63.82±0.02%. 1) Repeatability of
the equipment was tested by taking 2 measurements 20 min apart (n=16). 2)
Measurements were taken before and 60 min after 5-min heated eye mask wear
(Eyegiene®, US) (n=10) to test for changes in ocular surface
temperature and tear evaporation. Tear evaporation rates were calculated based
on ocular surface temperature profiles and controlled
for body and room temperature as well as room humidity using principles of
thermodynamics. Statistical comparisons were performed using paired t-test with
p<0.05.
RESULTS:
1) There were significant correlations between the first and
second measurements of ocular surface temperature (r=0.94) and tear evaporation
rates (r=0.98) (p<0.01). The coefficients of repeatability were 0.42˚C for ocular surface temperature and 6.78 Wm-2 for tear
evaporation rates. 2) Ocular surface temperature before heat therapy was
33.66±0.53˚C which significantly decreased to 32.50±0.97˚C after heat
application (p<0.01). Tear evaporation rates significantly increased from
65.64±12.51 to 78.72±21.53 Wm-2 following heat treatment
(p<0.01).
