To evaluate the tear film layer in patients with dry eye and in normal subjects by measuring the corneal temperature with infrared radiation thermography.

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.

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).

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.