Since the condition occurs within 12 months of initiating therapy, Dr. Johnson recommends conducting examinations at baseline and 4, 8, and 12 months, followed by annual ophthalmic exams.

Amiodarone was introduced in 1961 as an anti-anginal agent and was also found to be helpful in several cardiac arrhythmias.

To help address this shortcoming, Dr. Johnson conducted a retrospective review of charts at the Mason Eye Institute from 1990 to 2002 for cases of optic neuropathy in association with amiodarone use. A literature search was also conducted. He reported the results at the American Academy of Ophthalmology (AAO) annual meeting in New Orleans last fall.

Dr. Johnson and his colleagues identified 812 patients with optic neuropathy, of whom 21 (3%) were using amiodarone. Ten patients were excluded because of comorbid diseases such as proliferative diabetic retinopathy and acute hypotension, which could contribute to vision loss. This left 11 patients from hospital files, while 44 cases were found in the world literature.

Among these 55 cases, 87% were men and 13% were women. Mean age was 62 years. The review showed 42% of patients had hypertension, and 12% had diabetes.

More than 10% of patients were asymptomatic at their initial clinical examination. About 90% had vision loss, consisting of sudden onset of vision loss in 40% of cases and insidious onset in about 50%.

Visual acuity (VA) ranged from 20/15 to light perception, with a median VA of 20/30. In addition, 20% had legal blindness with VA 20/200 or worse.

Visual outcomes data showed that 40% had an improvement in VA after discontinuing medication, while 50% showed no change, and an additional 10% had further decline. Visual field loss was generally permanent when present. About 40% of patients had color vision loss.

About 80% of patients were taking amiodarone in standard doses of 400 mg or less. Intravenous use of amiodarone appeared to be associated with faster onset of disease, with one case occurring within 72 hours of intravenous use.

"However, in general, with oral ingestion, the median onset of optic neuropathy is 4 months, and 90% will occur within 12 months if present," Dr. Johnson said.

"One may ask: 'Isn't amiodarone optic neuropathy the same thing as NAION or and isn't cardiac arrhythmia a risk factor for NAION?' " Dr. Johnson said.

"Certainly there are overlaps in these conditions but there are some differences," he added. "There are also risk factors for NAION, but cardiac arrhythmia has never been shown by itself to be a risk factor for NAION."