PURPOSE: To evaluate the tear film layer in patients with dry eye and in normal subjects by measuring the corneal temperature with infrared radiation thermography. METHODS: One eye of each of 13 patients with dry eye and one eye of each of seven normal subjects were evaluated randomly. The corneal temperature was measured continuously with a recently improved infrared radiation thermography technique. We calculated the k value, which reflected the steepness of the corneal temperature change. The bigger the k value was, the more rapid was the decrease in corneal temperature, and this was directly related to increased evaporation. RESULTS: With normal blinking, the mean k value for patients with dry eye (5.6 ± 2.9 per second) was significantly less than that in the control subjects (9.3 ± 5.0 per second; P < .05). Keeping the eyes open after closing the eyes significantly decreased the k values compared with normal blinking in both groups (P < .05). CONCLUSIONS: Our findings demonstrate the usefulness of this method of measuring corneal temperature to evaluate the tear film layer. High-speed, high-resolution thermography detected subtle changes in corneal temperature with enhanced sensitivity and spatial and temporal resolution. We found that the mean k value, and therefore the rate of decline in corneal temperature in patients with dry eye, was significantly less than that in normal subjects. The k value may therefore reflect tear film layer stability. The measurement of the changes in the corneal temperature can thus give us valuable information on the tear film layer.
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