Abstract
Abstract: :
Purpose: To determine the change in ocular redness (measured objectively) accompanying ocular surface heating and cooling. Methods: Bulbar redness (CIE u`) on the temporal conjunctiva was measured continuously using a computer controlled Photoresearch Spectrascan650® Photometer under fixed illumination. The illuminant, 35 cm from the subject, was a 120 W incandescent source. An infra-red filter could be interposed in front of this source. Bulbar conjunctival temperature was measured using a Tasco-THI 500 infrared thermometer. The temperature and redness data were acquired on the same time scale at 5Hz using software written in MATLAB. In ten subjects the temperature and redness was measured in three, 2 minute phases first with fluorescent illumination, then with the incandescent lamp turned on and finally with the incandescent lamp output filtered using the infrared filter. Since the infrared filter causes change in the chromaticity only the slopes of increasing and decreasing redness were considered for analysis. Results: Ocular surface temperature increased during the period of incandescent illumination by approximately 2 degrees with a mean time constant of 31.3 sec. When the infra red filter was in place, the surface temperature reduced to baseline, with a time constant of 38.4 sec. During the phase of temperature increase, ocular surface redness monotonically increased and during the time the infra red filter was in place, redness steadily decreased. Slopes of increasing redness and decreasing redness without and with the filter respectively, were statistically different (p = 0.000). The absolute rate of decline in redness was also statistically different from the rate of increase in redness (p = 0.034). Conclusion: Changes in bulbar conjunctival redness occur simultaneously with changes in the temperature of the ocular surface. Ocular redness increases with ocular surface heating and decreases with a return to normal ocular surface temperature but the dynamics of the increase and decrease is not the same.
Keywords: conjunctiva • anterior segment • cornea: tears/tear film/dry eye