Spectroradiometer helps evaluation of CAC, ocular agents

March 1, 2005

La Jolla, CA—As a result of a desire to find more objective ways to measure erythema and edema in patients affected by conjunctival allergies, researchers undertook a conjunctival allergen challenge (CAC) study comparing epinastine HCl (Elestat, Allergan) and olopatadine HCl (Patanol, Alcon Laboratories).

Allergen challenge studies are commonly used to evaluate antiallergic and anti-inflammatory drugs, said Mitchell Friedlaender, MD, head of the division of ophthalmology at the Scripps Clinic in La Jolla, CA. Response to therapy typically is assessed by observation of the reaction and grading erythema and edema on a scale of 1 to 4.

"The spectroradiometer is very precise," he said. "It measures the amount or intensity of reflective light. Every color has a different value on x-y coordinates, so you can plot each one on a graph. That is why we did the study, to measure reactions to CAC objectively and to try to determine precise differences and eliminate differences from one center to the next."

In the study, a randomized comparison of prophylactic use prior to CAC, epinastine and olopatadine demonstrated equivalent effects on objective measures of erythema and edema. Epinastine reduced itching significantly more than did olopatadine, as rated by patients.

"We didn't demonstrate any difference in redness or swelling between the two types of eye drops," Dr. Friedlaender said.

The study involved 20 patients with a history of conjunctival allergy. In each patient, erythema was evaluated by spectroradiometry. To evaluate edema, the investigators used a fractional millimeter reticule placed in the eyepiece of a slit lamp to measure the width of the lower lid margins and the width of the lateral edge of the bulbar conjunctival plicae.

During week 1, the patients underwent CAC by topical application of cat dander, grass, or ragweed allergens until a moderate allergic conjunctival reaction occurred. During week 2, one drop of the allergen dose that produced the moderate reaction was instilled to confirm the allergic response. The eyes were then randomly assigned and treated 10 minutes after CAC with one drop of naphazoline HCl 0.025% and pheniramine maleate 0.3% or one drop of saline.

"We were trying to show that if you use a vasoconstrictor drop you could demonstrate a change to a less intense red," said Dr. Friedlaender. "The idea was to demonstrate a change in the u9 value on the spectroradiometer, which would indicate that the amount of redness was reduced when we instilled a vasoconstrictor drop."

During the third week, the eyes were randomly assigned to treatment 10 minutes before CAC. One drop of epinastine 0.05% was instilled in one eye, and one drop of olopatadine 0.1% was instilled in the other eye.

Erythema was measured 10 minutes before and 10 minutes after instillation of eye drops or allergen by means of a spectroradiometer. Room illumination was kept constant, and from a distance of 20 inches, a 5-mm focusing spot was placed on the inferior bulbar conjunctiva, with the eye in an upward gaze. The ú and v9 coordinates, as defined by the 1976 Commission Internationale d'Eclairage, were recorded, and three consecutive readings were averaged.