Loss and recovery of corneal sensitivity following photorefractive keratectomy for myopia.
BACKGROUND
Photorefractive keratectomy affects corneal innervation in a new, and drastic, way. This inevitably results in a significant loss of corneal sensitivity. This paper investigates the pattern of sensitivity loss and recovery following PRK for low to moderate myopia.


METHODS
Patients were recruited for two separate studies. Longitudinal Study: 10 patients, treated with a -6.00 D/6 mm PRK ablation, were examined over a 1-year period. Transverse Study: A comparison was made between 35 non-contact lens wearers, 80 contact lens wearers, and 60 patients who underwent five different PRK treatments, 1 year previously. Corneal sensitivity was assessed using the Non-Contact Corneal Aesthesiometer at four corneal locations: centrally, temporally, medially, inferiorly, on all patients.


RESULTS
Longitudinal Study: Corneal sensitivity was significantly reduced at week 1, with a further significant reduction at week 2. A gradual recovery in sensitivity then followed to reach preoperative levels by 1 year. Transverse Study: There was no significant difference in corneal sensitivity found as a result of different PRK ablation depths. The depth of ablation was not a factor in corneal sensitivity recovery in low to moderate myopic corrections. Corneal sensitivity in the PRK treated eyes was significantly lower than in the control groups.


CONCLUSIONS
The immediate loss of corneal sensitivity after surgery was due to the total removal of the corneal epithelial nerve supply and a substantial portion of the underlying stromal nerves. The further decrease at week 2 was probably due to the new epithelium acting as barrier to stimulation. The gradual recovery of corneal sensitivity was most likely caused by epithelial reinnervation within the ablation zone, but this was still below normal levels at 1 year after surgery. Corneal nerve function demonstrates a biphasic pattern of loss and recovery following the excimer laser correction of low to moderate myopia.
Murphy
P J
PJ
Department of Vision Sciences, Glasgow Caledonian University, Glasgow, United Kingdom. pmu@gcal.ac.uk
Corbett
M C
MC
O'Brart
D P
DP
Verma
S
S
Patel
S
S
Marshall
J
J
D000328:Adult; D000368:Aged; D003263:Contact Lenses, Hydrophilic; D003315:Cornea / Q000294:innervation / Q000503:physiopathology* / Q000601:surgery; D005500:Follow-Up Studies; D006801:Humans; D054018:Lasers, Excimer; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology* / Q000601:surgery; D009882:Ophthalmic Nerve / Q000503:physiopathology* / Q000601:surgery; D018903:Photorefractive Keratectomy; D011184:Postoperative Period; D011379:Prognosis