Corneal pain evoked by thermal stimulation

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Abstract
The thermal sensitivity of the eyelid and cornea was compared using an automated apparatus to produce stimulus pulses of known magnitude and duration over the range 33-45.degree. C. Human subjects reported only temperature sensation when the skin of the upper eyelid was tested; corneal stimulation in the same subjects was always perceived as nociceptive. The possibility that other ocular tissues may be involved in the pain responses was unlikely by direct experimentation or by calculation of heat flow in those tissues. Cornea and eyelid thresholds were compared in relationship to the structural and physical properties of these tissues. The nerve endings of the corneal epithelium are less sensitive to temperature change when compared to the thermal receptors of the eyelid. The cornea is useful for the experimental study of pain.