Application of video thermography for the evaluation of tear film layer

Purpose. When tears evaporate, the corneal temperature decreases due to the evaporation heat. Thus the change in corneal temperature reflects the condition of the tear film layer. We applied these funadmentals to tear film layer. Methods. The corneal temperature at a certain period can be described by the following equation.: T=(T₀-T_∞)e^-kt+T_∞ [T: temperature (°c), T₀: temperature just after blink, T_∞: temperature in equilibrium, t: time in second after blink, k: temperature coefficient]. The k shows the steepness of the change in the corneal temperature. The corneal temperature of dry eye patients (N=4) and normal volunteers (N=7) was measured with normal blink every 1/60 second at the center of the cornea by video thermography and ks were calculated. Results. Average inter blinking time of dry eye patients was 1.88±0.41 seconds whereas it was 3.26±2.06 seconds in normal volunteers. With the shortened inter blinking time in dry eye patients less than two seconds, there were no statistical differences in ks between two groups. The calculated ks of each patient varied from blink to blink normal volunteers dry eye patients Average ks -1.88 ± 0.51 -1.54 ± 0.47 (p=0.33) Range of ks -0.97 ∼ -2.21 -0.98 ∼ -2.44 Conclusions. This study demonstrated that as far as the inter blinking time was less than two seconds in dry eye patients, the corneal surface was fully wet during the first two seconds following the blink. Furthermore the thermo-graphic data suggested that the tear film spread over the cornea with certain variation of thickness from blink to blink.