Symptoms of conjunctivitis (tearing, redness and itching) frequently occur in patients with allergic rhinitis. The pathophysiology underlying these symptoms remains to be elucidated. The symptoms probably arise via a combination of mechanisms including direct contact of natural pollen with the conjunctiva and reflex mechanisms originating in the nose.
Pollen exposure can result from direct hand transfer of pollen to the conjunctiva or, conceivably, from the forceful blowing of air, containing nasal secretions with antigen, up the nasolacrimal duct. The latter mechanism would be considered extremely unlikely because of the location of the nasolacrimal duct under the inferior turbinate (the duct's location is in an area with little pollen exposure) and the considerable force of air needed to cause reverse flow in the duct. The latter would also be true for topically applied intranasal drugs reaching the conjunctiva via the nasolacrimal duct, whereas the administration of medications to the conjunctiva frequently results in these medications reaching the nose via the nasolacrimal duct.
In support of direct contact of pollen as a source of ocular symptoms in patients with allergic rhinitis is the observation that pollen can be washed out of the conjunctiva on windy days, although the amount is 10 fold less than the amount of pollen recovered simultaneously from the nose. Additionally, beginning with Noon in the early 1900s, and subsequently shown by others, direct conjunctival challenges induce ocular symptoms. Thus, direct contact is a plausible explanation, but its relative contribution to eye symptoms in allergic rhinitis is unknown. Since topical intranasal steroids are known to reduce eye symptoms and the chance of them reaching the eye by systemic absorption or directly when administered intranasally are very slim, the investigators would postulate that direct allergen contact at the conjunctiva is a small contributor to the overall ocular symptom complex.
Reflex mechanisms within the nose have been shown to occur universally in response to nasal challenge with antigen. Nasal challenge with antigen induces a reflex in the contralateral nasal cavity, known as the nasonasal reflex. This reflex can also be initiated by nasal challenge with cold, dry air and histamine. The contralateral response to antigen, cold dry air and histamine is blocked by topical anticholinergic agents applied to the contralateral side, suggesting that the efferent limb is parasympathetically mediated. Histamine is only released on the side of challenge with antigen but oral H1 antihistamines reduce the contralateral response to unilateral nasal allergen challenge, suggesting that histamine contributes to the initiation of the reflex. The eye is richly innervated by parasympathetic nerves which enter the eye after running in conjunction with the parasympathetic input to the nasal cavity. The investigators, therefore, hypothesize that the conjunctiva will respond to nasal allergen in a manner similar to the contralateral nasal cavity.
Purpose: The investigators will study whether antigen-induced nasal reflexes cause eye symptoms. The investigators suspect that reflexes occur between the nose and the eye, and contribute substantially to eye symptoms in allergic patients during the allergy season. The investigators propose to demonstrate that nasal challenge with antigen leads to increased lacrimation.