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L. Krokhmal, P.J. Gomes, M.B. Abelson; An Analysis of Patient Sensitivity to Allergen in the Conjunctival Allergen Challenge (CAC) Model over a Three Year Period . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3750.
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Purpose: The human allergen challenge model utilizes specific ocular allergens to induce a reproducible inflammatory response that induces the signs and symptoms of allergic conjunctivitis. The purpose of this survey was to determine whether sensitivity to an allergen for an individual changes over a period of three years. Methods: The study population was derived from allergen challenge clinical trials over a period of three years. The allergen challenge was performed with a serially diluted allergen. The concentration of allergen at which the patient reacted positively was determined at the start of each study. The lowest dose of allergen was instilled into the conjunctival cul-de-sac bilaterally. If the patient failed to react positively within 10 minutes, increasingly concentrated doses were instilled at ten minutes intervals until a positive reaction (itching and hyperemia) was elicited. For each patient an increase or decrease (based on the first study) in allergen concentration required to induce a positive reaction for a 3-year period was determined. Results: A total of 100 patients were analyzed. The concentration of allergen required to induce a positive conjunctival allergen challenge reaction increased for 65% of patients, decreased for 14% of patients and stayed the same for 21% of patients. The majority (78%) of subjects allergic to ragweed required an increase in allergen concentration at a future visits. For those 65 patients that had an increase in allergen concentration, the average change was by 1.8 dilutions. For those patients that had a decrease in allergen concentration, the average change was by 1.1 dilutions. Conclusions: The results suggest that the threshold dose of allergen required to induce an ocular allergic response in an atopic individual changes over time.
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