The Effect of Lid Closure upon the Ocular Temperature Gradient.

The effect of lid closure and opening upon the ocular temperature gradient was studied in the rabbit eye by determining the changes in temperature of the anterior surface of the central cornea, the pupillary area of the anterior chamber, and the midiris area of the posterior chamber. With lid closure the temperature of all three areas rose to a similar level of 37.7° C. so that the ocular temperature gradient was essentially abolished. The time for rise of temperature with lid closure was greater than the time for fall ivith lid opening in the posterior chamber. As an incidental observation, it tuas noted that loith the lids open the mean temperatures of all three areas were generally lower in the horizontal head position (visual axis perpendicular to the ground) than those in the vertical head position (visual axis parallel to the ground). This observation is interpreted as due to a decreased heating of the cornea by the lack of a flmoing tear film because of pooling in the conjunctival cul-de-sac with the head in the horizontal position. The physiologic position of the lids will also create in the anterior segment of the eye, superiorly and inferiorly, a peripheral to central ocular temperature gradient in addition to the existing posterior to anterior gradient. The blink reflex is too infrequent in the rabbit to influence the ocular temperature gradient, but closure of the lids such as during sleep will abolish the temperature gradient while lid retraction or globe protrusion will increase the temperature gradient.