Conjunctival decongestion

Pharmacology Epinephrine, a direct-acting sympathomimetic agent, acts on and receptors. Topical application, therefore, causes conjunctival decongestion (vasoconstriction), transient mydriasis (pupillary dilation), and reduction in intraocular pressure (lOP). It is believed lOP reduction primarily is caused by reduced aqueous production and increased aqueous outflow. The duration of decrease in lOP is 12 to 24 hours. 

Eye drops are available containing an antihistamine, antazoline sulphate 0.5%, and xylometazoline hydrochloride 0.05%. The latter has vasoconstrictor action and is included as a conjunctival decongestant. This preparation can be used for the short-term treatment of hayfever symptoms, but prolonged use may raise intraocular pressure and precipitate glaucoma. The drops are used twice or three times daily and are suitable for children from 5 years of age. 

Functional antagonists of mediators of allergy, a) a-Sympathomi-metics, such as naphazoline, oxymeta-zoline, and tetrahydrozoline, are applied topically to the conjunctival and nasal mucosa to produce local vasoconstriction, and decongestion and to dry up secretions (p. 90), e.g., in hay fever. Since they may cause mucosal damage, their use should be short-term. 

Phenylephrine is an effective mydriatic agent frequently used to facilitate examination of the retina. It is also a useful decongestant for minor allergic hyperemia and itching of the conjunctival membranes. Sympathomimetics administered as ophthalmic drops are also useful in localizing the lesion in Horner s syndrome. (See An Application of Basic Pharmacology to a Clinical Problem.)... 

Phenylephrine, the oldest of the currently available agents, is a synthetic adrenergic agonist. It differs chemically from epinephrine by the absence of the hydroxyl group on position 4 of the benzene ring. At the concentrations used for ocular decongestion, phenylephrine causes vasoconstriction by direct stimulation of a-adrenergic receptors on the conjimctival vasculature. The resultant clinical effect is usually a decrease in conjunctival hyperemia and edema. 

At the 0.12% concentration used for ocular decongestion, phenylephrine can occasionally dilate the pupil.This effect is most likely to occur if the corneal epithelium is compromised. Moreover, with long-term use phenylephrine can cause a rebound conjunctival congestion and result in conjunctivitis medicamentosa. For this reason the use of phenylephrine has declined. 

Oxymetazoline is available as an ocular decongestant at the 0.025% concentration. Oxymetazoline has been demonstrated to be useful in patients with allergic conjunctivitis and has been demonstrated to improve symptoms of burning, itching, tearing, and foreign body sensation in patients with moderate to severe conjunctival hyperemia. Onset of action can be as early as 5 minutes after instillation, with peak effects at 60 minutes, and the effect can last up to 6 hours. Oxymetazoline 0.025% does not seem to alter lOP or affect pupil size or accommodation. 

Conservative treatment of zoster-associated conjunctivitis, including cold compresses, lubricants, and decongestants, carries the lowest risk of treatment-related complications. Treatment of the acute conjunctivitis with topical broad-spectrum antibiotics may help to prevent secondary bacterial infection. Increased patient comfort by reduction of conjunctival inflammation may be affected by the use of topical steroids. Often, a combination antibiotic-steroid is used to accomplish both of these goals. In contrast to herpes simplex infection in which steroids are specifically contraindicated, topical steroids do not exacerbate herpes zoster infection. If steroids are used, the patient should be carefully monitored for intraocular pressure elevation. 

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