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Ranjini Kottaiyan, Geunyoung Yoon, Gheorghe Salahura, James M. Zavislan, James V. Aquavella; Time-Resolved Ocular Surface Cooling Rate using Thermal Imaging. Invest. Ophthalmol. Vis. Sci. 2012;53(14):110.
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© ARVO (1962-2015); The Authors (2016-present)
To quantify the ocular surface temperature (OST) in real time in normal and dry eye sub-groups.
Fifteen eyes of 5 normal, 5 aqueous deficient dry eyes (ADDE) and 5 with meibomian gland dysfunction (MGD) were chosen for the study based on clinical dry eye evaluation. Normal subjects had a Schirmer’s value ≥ 10mm/5 mins and a fluorescein tear break-up time >5 secs with no surface staining. MGD was diagnosed based on the obstructive findings of the gland orifice on a slit lamp and decreased meibum expression on moderate digital pressure. ADDE subjects had Schirmer’s <10 mm. The subjects were instructed to blink once every 5 seconds and the OST measurements were taken using an infrared thermal camera (FLIR Thermovision), with an acquisition speed of 30 frames/second. The blink intervals were analyzed using custom MATLAB software to calculate the initial temperature immediately after eye opening. Average OST was computed over a central elliptical area on the cornea from which the OST was calculated. The slope of OST over each second was computed to evaluate the OST cooling rate over each second in each of the blinks. Inter-blink variability and OST cooling rates between the groups were studied.
The normal group exhibited very little cooling of the ocular surface over 5 seconds after a blink, with an OST cooling rate of 0.07 oC/sec and 0.04 oC/sec over the first and second seconds respectively with no change in the OST rate after that. The MGD group exhibited a rapid cooling of the ocular surface at a rate of 0.21oC/sec over the first second and 0.07 oC /sec over the second second and these rates were found to be significantly different than in normals (P=0.01 and P=0.04 respectively). There was no significant cooling occurring after 3 seconds in both the groups. The ADDE group also had a rapid cooling of the ocular surface at a rate of 0.25 oC /sec and 0.08 oC/sec in the first and second seconds respectively, and the rate of cooling stabilized after that. This rate over the first second was found to be significantly faster than in normals (P=0.02). Starting 3 seconds onwards, the OST cooling rate stabilized in the dry eye groups and was close to that of the normal group with no significant differences. The initial OST after a blink was significantly higher in the MGD group (35.8 ± 0.4oC) than in the normal (35.4 ± 0.4oC, P=0.03) and ADDE groups (35.1± 0.7 oC, P=0.005) with no significant inter-blink variability within the groups.
Time resolved analysis of the cooling rates using thermal imaging has the potential to provide objective implications of the relationship between tear evaporation and stability in normal and dry eye patients.
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