Corneal epitheliopathy of dry eye induces hyperesthesia to mechanical air jet stimulation

PURPOSE: To evaluate corneal sensation in different groups: normal subjects, dry eye patients, and patients with and without dry eye after laser in situ keratomileusis (LASIK) using the modified Belmonte gas esthesiometer. DESIGN: A retrospective, clinic-based, case control study. METHODS: We evaluated 20 normal subjects, 20 dry eye patients, 20 post-LASIK patients without dry eye, and six post-LASIK patients with dry eye. The corneal sensation was measured with the modified Belmonte gas esthesiometer that uses two different stimuli to assess mechanical and polymodal receptors on the corneal surface. Mechanoreceptors were assessed by 2 second pulsed air jets of variable intensity. Polymodal receptors were measured by stimulating the corneal with 2-second pulsed air jets of varying concentrations of CO2, a gas that is converted to carbonic acid on contact with the corneal surface. The main outcome measure was determining corneal sensation. RESULTS: The mean +/- standard deviation ( +/- SD) age was similar in all groups. The mean mechanical threshold was 61.50 +/- 20.07 ml/min in the normal group (n = 20), 34.60 +/- 21.09 ml/min in the dry group (n = 20, P < .05 vs normal), 99.50 +/- 47.40 ml/min in the post-LASIK group (n = 20, P < .01 vs normal), and 50.00 +/- 15.49 ml/min in the post-LASIK patients with keratitis sicca (n = 06, P < .05 vs post-LASIK). The percentage of CO2 to elicit discomfort was similar in all groups (P > .05). No sex-related differences were noted (P > .05). There was a significant inverse correlation between the threshold of mechanical stimulation and the severity of corneal fluorescein staining. CONCLUSIONS: The Belmonte modified noncontact esthesiometer is a sophisticated instrument that can assess different types of corneal sensory receptors. Patients with dry eye were hypersensitive to the air jet stimulus of this instrument, and this appears to be due to altered corneal epithelial barrier function. Profound hypoesthesia was observed after LASIK and similar to dry eye, post-LASIK patients with dry eye were sensitized. These findings provide new insight into the hypersensitivity to environmental stresses, particularly air drafts experienced by dry eye patients.