Abstract
Purpose: :
To explore whether corneal sensitivity to mechanical, chemical and thermal stimuli is affected in iritis patients.
Methods: :
Twenty eight voluntary subjects participated in the study. Acute iritis patients who attended the acute ward of the Helsinki University Eye Hospital were examined with a non-contact gas esthesiometer (Belmonte OPM, Deriva Global) to measure corneal sensitivity threshold to mechanical (air flow between 0 and 200 ml/min), chemical (0 to 80% CO2 in air, at subthreshold flow) and cold (air at subthreshold flow inducing corneal temperature changes between 0.1º and -5.9ºC) stimulation. Sensation threshold was defined as the lowest stimulus intensity of each modality evoking a conscious sensation. Schirmer 1 test was used to measure tearing rate. Data from iritis patients were compared with those of a sex- and age-matched control group.
Results: :
The mean sensitivity threshold values for mechanical stimulation were not significantly different in iritis patients in comparison with controls (130±20 vs. 108±4 ml/min, n=10 and 18; p=0.29, t-test). Threshold for chemical and cold stimulation were significantly higher in iritis patients in comparison with control subjects (Chemical= 48±9% vs. 21±5% CO2; p=0.008. Cold= -4.3±0.5º vs. -0.8±0.2ºC; p<0.001). Tearing rate was significantly increased in iritis patients (45±3 vs. 31±2 mm; p<0.001).
Conclusions: :
Patients with iritis exhibit a lower corneal sensitivity to chemical and cold stimuli whereas mechanical sensitivity remains unaltered. These sensory disturbances presumably reflect inflammation-induced changes in the excitability of trigeminal ganglion polymodal and cold-sensitive neurons, perhaps those that innervate both the iris and the cornea. Nevertheless, the possibility that the number of nociceptive fibers decreases consecutively to chronic inflammation cannot be excluded.
Keywords: innervation: sensation • iris • cornea: clinical science