Abstract
Purpose: :
To compare the ocular surface temperature (OST) in severe dry eyes secondary to Sjogrens and healthy normal eyes.
Methods: :
14 Sjogrens subjects (28 eyes) with severe dry eye (Tear break up time ≤ 4 seconds) and 14 normal subjects (28 eyes) were selected. After 20 minutes acclimation inside a controlled chamber of 24 ºC temperature / 45% humidity, a non-invasive infrared thermal camera was positioned in front of each eye to capture a 25 seconds video clip. The camera sensitivity to emitted radiation was 0.08ºC. The subjects were trained to blink only every 5 seconds and to stabilize their heads and eyes. Three Sjogrens subjects (6 eyes) were measured again after 30 minutes acclimation in the same chamber with 24ºC and much higher humidity of 85%. A modified Matlab software was used to select 5 specific areas for analysis on the ocular thermograph of fully opened eye. Temperature values of these spots were retrieved, plotted and analyzed.
Results: :
When comparing Sjogrens and normal groups, root of nose body reference temperatures were similar P=0.547. Initial immediate after-eye-open OST were also similar between the 2 groups. OST drop rates were significantly faster at all 4 ocular surface locations in Sjogrens than normals. At the central cornea location, the initial OST in Sjogrens was 34.07±0.64 vs. normals 34.03±0.51 ºC without significant difference. The drop rate of Sjogrens -0.276±0.099 was significantly faster than normal of -0.065±0.033 ºC/sec, P=0.000. The largest drop in Sjogrens was at 1 and 2 second while for normals, only the 1st second drop had significance. At the end of blink cycle, the central Sjogrens OST was significantly lower than normal (32.79±0.82 Vs 33.73 ±0.49), P=0.000. The temperature difference between the central and peripheral cornea location in Sjogrens group (1.19±0.42 ºC, peripheral warmer) was significantly greater than normal group (0.39±0.32, peripheral warmer), P=0.000. For the 6 dry eyes in higher humidity at the central cornea location, the OST had a significantly smaller drop rate (-0.177±0.040 ºC/sec) than in normal humidity environment, P=0.010.
Conclusions: :
The OST of dry eyes secondary to Sjogrens has a much faster decrease than normals after blink. Much of the cooling occurs immediately after eye opening and more evident in the central location. High humidity environment decreases tear evaporation and improves dry eye condition. Infrared thermal imaging can be used as a clinical tool.
Clinical Trial: :
http://www.clinicaltrials.gov NCT01228929
Keywords: cornea: tears/tear film/dry eye • imaging/image analysis: clinical • autoimmune disease