Amiodarone and optic neuropathy

Abstract

inc the is The case report literature would suggest that amiodarone can produce a toxic optic neuropathy. Patients receiving amiodarone have lost vision. However, a quandary exists when any drug is implicated as a cause of optic neuropathy—a drug toxicity can be mimicked by idiopathic anterior ischemic neuropathy. The 2 entities can have overlapping characteristics. Key features of toxic optic neuropathies are simultaneous bilaterality, progression at dose-related rates, and occurrences at higher incidences than can be explained by idiopathic anterior ischemic optic neuropathy. Significant reversibility on discontinuation of the drug, if it occurred consistently, would also be an important feature. Ethambutal provides a good example of such a toxic agent. Idiopathic anterior ischemic optic neuropathy, in contrast, is usually unilateral at onset (with estimates of simultaneous or subsequent contralateral involvement ranging from 10%-73%), attacks an optic nerve only once (though that initial visual loss can progress stepwise for up to 3 weeks), and causes vision loss that is not completely reversible (with 6 months follow-up, 43% improved≥3 lines of vision). Awide variety of etiologies have been attributed to idiopathic anterior optic neuropathy as follows: cardiovascular (nocturnal hypotension, sleep apnea), immunologic (Chlamydia seropositivity), genetic (glycoprotein 1bα gene), metabolic (hyperhomocystinemia), and local pathologic conditions (“crowded” optic disc, optic disc traction from vitreous adhesions). The prior annual incidence estimates of amiodaronetoxic optic neuropathy have been based on the retrospective case report literature. Those range from 0.36% (a 5-year incidence of 1.79%) to 2%. The incidence estimates for idiopathic anterior ischemic optic neuropathy in patients ≥50 years are far less—0.0023% to 0.03% (10 year incidence 0.3%). Three lines of data have recently raised doubts that amiodarone is toxic to the optic nerves: (1) pharmaceutical sales of amiodarone; (2) Food and Drug Administration (FDA) records of amiodarone-associated optic neuropathy; and (3) a prospective, double-masked, randomized trial. on