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Waldir Neira, Timo T. Tervo, M.Carmen Acosta, Juha M. Holopainen, Carlos Belmonte, Juana Gallar; Corneal Sensitivity To Selective Stimulation In Iritis Patients. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1790.
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To explore whether corneal sensitivity to mechanical, chemical and thermal stimuli is affected in iritis patients.
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.
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).
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.
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