The association between corneal cold, chemical and mechanical thresholds measured using a Belmonte esthesiometer.

Abstract

Abstract: : Purpose: To examine the association between corneal mechanical chemical and cold thresholds measured using a pneumatic esthesiometer. Methods: 20 normal subjects had central corneal thresholds measured using a Belmonte esthesiometer. Thresholds were estimated using an initial ascending method of limits and then the method of constant stimuli. The stimulus temperatures (20 deg or 50 deg), flow rate, proportions of CO2 and subjects responses were controlled or accumulated by the computer. Separate detection (cold) and discomfort thresholds for 20 deg pneumatic stimuli, detection thresholds for 50 deg pneumatic stimuli and detection thresholds (at half the mechanical flow thresholds) for %CO2 at 50 deg were derived. Correlation analysis was used to estimate the association between the thresholds. Results: At threshold, the 20 deg stimulus felt cool and the 50 deg (mechanical and chemical) stimuli were uncomfortable or painful. The strongest correlation was between the 50 deg detection and the 20 degree discomfort threshold (r=0.61, p=0.005), followed by the correlation between the 50 deg mechanical and chemical thresholds (r=0.60, p=0.005). The weakest correlation was between the 20 deg cold detection and discomfort thresholds (r=0.36, p=0.117). Conclusions: Because of the relatively good associations between thresholds, the results suggest that although these mechanical and chemical nociceptive and cold corneal channels might be separate, subjects who are sensitive to one are generally sensitive to the others (and vice versa). This has implications in understanding the underlying corneal neural mechanisms.

Keywords: contact lens • cornea: tears/tear film/dry eye • cornea: basic science