Relative sensitivity of the ocular trigeminal, nasal trigeminal and olfactory systems to airborne chemicals

We measured thresholds for eye irritation and odor in homologous series of alcohols (ethanol, 1-butanol, 1-hexanol and 1-octanol), ketones (2-propanone, 2-pentanone, 2-heptanone and 2-nonanone), and alkylbenzenes (toluene, ethyl benzene and propyl benzene). Eye irritation thresholds were well above odor thresholds for all series. Both sensory thresholds declined with carbon chain length, a trend that has implicated lipophilicity in the potency of these and related stimuli. Eye irritation thresholds were remarkably close to nasal pungency thresholds obtained previously in persons lacking olfaction (i.e. anosmics). The agreement between the two thresholds implies that, despite differences in the mucus layer at the two sites and in the epithelial tissue itself, there is remarkable similarity at the site of stimulation. As a practical matter, the eyes could serve as the sites to assess potency for induction of nasal pungency, an assessment previously limited to testing anosmics. Presumably, for our brief stimulus presentations (1-3 s), the differences between ocular and nasal mucosae have little relevance to chemical sensitivity. Studies of the ability of homologous chemical series to evoke threshold eye irritation, nasal pungency and odor not only have practical value, but also can help to define the physicochemical properties of the receptor and perireceptor biophases.