Conjunctival temperature: a measure of ocular decongestant and anti-inflammatory activity

A new experimental method is presented that permits objective evaluation of ocular decongestant and anti-inflammatory activity following systemic or local administration of drugs to the rabbit eye inflamed with mustard oil. The inflammation produced by mustard oil is characterized by conjunctival hyperemia and chemosis and is measured by the conjunctival sac temperature. Although a 2% suspension of acetylsalicylic acid (0.1 ml) applied topically to the eye did not markedly reduce conjunctival temperature compared to the control eye, oral administration of 300 mg/kg showed a significant reduction throughout the duration of the experiment. In addition to the anti-inflammatory agent, acetylsalicylic acid, the antihistaminic, antazoline phosphate 0.5% and a vasoconstrictor or decongestant, naphazoline hydrochloride 0.05% were applied individually and in combination (Vasocon-A) locally in the conjunctival sac. Both antazoline phosphate and naphazoline hydrochloride reduced congestion and conjunctival sac temperature while the combination reflected the action of the individual ingredients. The palliative effect of antazoline phosphate indicates that this drug administered topically readily antagonizes histamine in the inflamed eye. There was no corneal anesthesia after instillation of Vasocon-A into the rabbit eye. Antazoline hydrochloride administered in up to 8 times the concentration in Vasocon-A did not induce corneal anesthesia which could be readily obtained with tetracaine hydrochloride.