Abstract
Purpose: :
On the bulbar conjunctiva, to examine the association between the pneumatic esthesiometer thresholds and the sensations induced by the stimuli at threshold.
Methods: :
20 normal subjects detected pneumatic stimuli presented using a computerized Belmont esthesiometer applying stimuli to the bulbar conjunctiva. Detection thresholds were obtained for 1) 20ºC and 2) 30ºC pneumatic stimuli, 3) 20ºC uncomfortable stimuli (each of was induced by varying flow rate) and 4) CO2 stimuli at 30ºC and half detection threshold flow rates. For the first 3, order was randomized and flow was systematically varied and in the latter, CO2 proportion was varied. An ascending method of limits was used to generate an initial estimate of threshold and then analogue rating scales were completed to quantify 6 attributes of the stimulus (eg., does sting–does not sting). Threshold was estimated using the method of constant stimuli and calculated from the psychometric functions using nonlinear regression . Associations were assessed using correlation coefficients and differences between means using repeated measures ANOVA’s.
Results: :
The 3 flow thresholds were different from each other (all p’s <=0.005) but there were no differences between psychometric function slopes (p=0.972). Only the correlation between 20ºC detection and 30ºC detection thresholds was significant (p=0.008). At threshold, for each stimulus, there were significant differences between stimulus attribute ratings (all p’s <=0.001), with the 3 flow stimuli each being rated highest as "cool" and the chemical stimulus being rated highest as "stinging".
Conclusions: :
The results suggest that there are differences between nociceptive and thermal processing channels of the conjunctiva and cornea and that, perhaps, corneal and conjunctival stimulation with the Belmonte esthesiometer are not the same (particularly temperature).
Keywords: innervation: sensation • contact lens • conjunctiva