[Methods] In anesthetized cats, a bilateral central corneal ablation (6.0 mm diameter, 70-4 depth) was performed after removal of the epithelium, using a excimer laser; 12-48 hr later, the ciliary nerves were dissected in the orbit and afferent, single nerve fiber activity was recorded using conventional electrophysiological techniques (Belmonte et al., J Physiol. 437: 709, 1991). von Frey hairs, pH drops caused with a jet of CO2 and temperature changes with cooled or wa/med air were respectively used to produce mechanical, chemical and thermal stimulation of the wounded area and of the peripheral cornea and episclera. Electrical stimulus was used to identify fibers branching inside the wounded area.

[Results] Fibers with receptive fields entering or bordering the wound, showed a spontaneous activity which was significantly higher than in fibers with distant receptive fields. Most of them were insensitive to mechanical and chemical stimulation of the wound, although some of them showed chemical but not mechanical sensitivity and in a few cases, they also responded to touching within the wound. The response of these fibers to mechanical and chemical stimuli was enhanced in the surroundings of the wound, being maximal in the borders.

[Conclusions] After PRK, sensory endings innervating intact areas nearby the wound became sensitized while a few endings within the injured tissues maintain a sensitivity to natural stimuli. Spontaneous and evoked activity in these fibers explain the presence of pain in human patients following this surgical procedure.

[Purpose] To study the spontaneous and stimulus-evoked activity of nociceptive fibers innervating the cornea, after photorefractive keratectomy (PRK).

Peer reviewed