Common drugs such as naphazoline, oxymetazoline, tetrahydrozoline, and phenylephrine hydrochloride are used as topical drops to cause temporary vasoconstriction of conjunctival vessels. This effect is mediated by α1-receptors. Other than providing temporal relief of hyperemia, they have no clear therapeutic benefit. Possible adverse effects include rebound vasodilation and conjunctival injection. The mechanisms of the adverse effects are unclear; possibilities include receptor desensitization and damage to the ocular surface as a result of vasoconstriction of arteries, which may involve activation of α2-receptors, and toxicity of preservatives. These medications can be abused by patients and may cause ocular surface toxicity. Systemic absorption of ocular adrenergic drugs is frequently sufficient to cause systemic effects, which are manifested in the cardiovascular system, the bronchial airways, and the brain (see the earlier section Adrenergic Drugs).
Although ocular decongestants are available as over-the-counter preparations, patients should be instructed not to use them on a long-term basis. Further, all efforts should be made to determine the etiology of the patient’s hyperemia and to target the source before use of these medications is considered.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.