Eye dryness sensations after refractive surgery: impaired tear secretion or "phantom" cornea?

The cornea is richly innervated by various functional types of sensory nerve fibers. When stimulated, these fibers evoke conscious sensations of different quality including ocular dryness, discomfort, and pain. Refractive surgery involves a variable degree of damage to corneal nerves. This leads to an altered expression of membrane ion channels at the injured and regenerating nerve fibers, giving rise to aberrant spontaneous and stimulus-evoked nerve impulse firing. It is speculated that these abnormal sensory discharges are read by the brain as ocular surface dryness. This would explain the high incidence of eye dryness sensations after photorefractive surgery, which are experienced by a large number of patients despite the often modest disturbance of tear secretion. Therefore, drugs that reduce abnormal activity in injured nerves may represent a therapeutic alternative for eye dryness sensations after refractive surgery.