Ocular Surface Temperature in Sjögrens Syndrome -- a Case Control Study

Abstract

Purpose: To study the interblink changes in Ocular Surface Temperature (OST) using thermal imaging in subjects with Sjögren’s syndrome (SS) compared to age-matched controls under standardized ambient temperature (75° F) and relative humidity (RH = 40%) conditions within a controlled environmental chamber.

Methods: 14 eyes of subjects with Sjögren’s syndrome (7 subjects) were included in the study along with 14 eyes of age-matched normal subjects. All patients included in the SS group fulfilled the AECG criteria for classification of SS. Normal eyes comprised of patients that reported no subjective dry eye symptoms. Images were taken in our controlled environmental chamber at 40% RH and 75 °F with a non-invasive infrared thermal camera (Thermovision SC325, FLIR System, sensitivity <0.05°C at 30 °C). The camera is sensitive to subtle temperature changes, has high magnification and resolution to capture the small palpebral aperture and detect subtle rapid changes of the OST. Thermal data was analyzed using custom software to calculate the OST in the central 9 mm of the cornea over the five sec. blink interval. Ocular outcome measures included: initial temperature, mean ocular surface temperature over the interval, and time segmented cooling rates. Statistical analyses were performed using t-tests.

Results: The average age of patients with SS was 54 years, and 55 years in control subjects. The mean OST over the 5 second blink interval was warmer in the normal eyes (34.66 ± 0.08°C) than in the dry eyes (34.18 ± 0.18°C) ( p<0.0001), with the normal group having a higher initial temperature (34.96 ± 0.59°C) in the first frame immediately after a blink than the Sjögren’s group (34.73 ± 0.48°C)(NS). Time segmented measures of ocular surface cooling showed that maximum decrease in OST happened within the first 0.5 seconds after a blink. This rate of cooling was greater in the Sjogren’s Syndrome group than in normals; -0.59°C /0.5 sec and -0.38°C /0.5 sec respectively (p<0.05). Both groups’ cooling rates stabilized after 2.5 seconds, though the Sjogren’s group maintained a greater rate of decline than the normal (-0.053°C in SS vs. -0.021°C over the 2 sec interval from 3-5 secs.

Conclusions: Ocular surface cooling rates are greater in subjects with SS compared to age-matched controls. This may reflect greater tear evaporation or the thinner tear film layer. Further research is needed to understand the clinical relevance of these findings.

Keywords: 486 cornea: tears/tear film/dry eye • 479 cornea: clinical science • 468 clinical research methodology