Comparison of thermal sensitivity of the forehead, lip, conjunctiva and cornea

¹ Department of Psychology, Florida State University, Tallahassee, Florida

The cornea is innervated by bare nerve endings of greater density than skin. If these act as thermal receptors, the cornea should be more sensitive to thermal stimulation than skin because of its dense innervation, surface proximity of the nerve terminals and absence of vascular system. Comparisons were made of the thermal sensitivities of the upper lip, forehead, conjunctiva and cornea. Although no thermal sensations were obtained from the cornea by applications of temperatures ranging from 20° to 55°C, all observers reported sensation changes at certain points on the temperature continuum. These were described in terms of irritation, whereas similar temperatures applied to the other sites felt cool, warm or hot. Comparison of the cool, warm and hot thresholds of the lip, forehead and conjunctiva showed them to be generally similar (P > 0.05). Stimulus temperatures at which corneal sensations changed were significantly different (P < 0.002) from the thresholds obtained at the other test sites. It is concluded that the cornea differs both quantitatively and qualitatively in its response to thermal stimulation from the other regions tested.

Note:
(With the Assistance of B. P. Childers and R. Webb)

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