Long-Term Corneal Sensitivity after PRK determined by Non-contact Gas Esthesiometry

摘要

Purpose: To evaluate the long-term (5-12 years) evolution of corneal sensitivity to mechanical and chemical stimuli after photorefractive keratectomy (PRK). Methods: Nineteen patients (12 male, 7 female; mean age 35.3; range: 21-55 years at the time of surgery) who underwent PRK for low to moderate myopia (mean spherical equivalent -3.0 D; range -2.5 to -8.0 D), and 14 control individuals (5 male, 9 female; mean age: 40.3, range: 28-54 years) were examined at 1 week, and 0.5, 2, 5 and at least 10 years (range 10.5-12 years) after surgery. Corneal sensitivity to mechanical (air flow between 0 and 260 ml/min) and chemical (0 to 80% CO2 in the air, at subthreshold flow) stimulation was tested with non-contact gas esthesiometry (original Belmonte esthesiometer: 1 week-2 years; modified Belmonte-CRCERT esthesiometer: 5years) using 0-10 Visual Analogue Scales (VAS) and performing intensity-response curves. The sensation threshold value and the slope of the intensity-response curve were calculated. Results: Corneal sensitivity to mechanical stimulation was present but significantly reduced 1 week after surgery when compared with controls (mechanical thresholds: 203?±49 vs. 105?±14 ml/min; slopes: 0.0044 vs. 0.0219 VAS unit/ml of flow, respectively). The decrease of corneal mechanical sensitivity was more pronounced 0.5 years after PRK and remained below control values 2 and 5 years postoperatively (thresholds: 267?±18; 260?±10, and 249?±13 ml/min, respectively). Corneal sensitivity to chemical stimulation was only slightly modified after PRK (slightly enhanced at 1 week but slightly reduced at 0.5, 2 and 5 years). Sensitivity to both mechanical and chemical stimulation presented normal values 10 years after PRK (mechanical threshold: 91?±12 ml/min, slope: 0.0218 VAS unit/ml of flow). Conclusions: Immediately hyperesthesia to chemical sensitivity is attributable to sensitization. The long-lasting reduction of corneal sensitivity to mechanical stimulation after PRK indicates that the transduction capacity to mechanical forces of injured nerve fibers is permanently impaired, contributing to the altered sensations experienced after PRK. New regenerating nociceptive corneal nerves slowly invade the denervated area, being responsible of the recovery of mechanical and chemical sensitivity observed at 10 years after PRK.