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Persons who have unilateral nonarteritic anterior ischemic optic neuropathy (NAION) that either is spontaneous or developed after cataract surgery should be cautioned that they are at increased risk for NAION after cataract surgery in the fellow eye.
"The rate of ON in the first 6 months after cataract extraction is estimated to be about 52 per 100,000 cases. This is five times higher than would be expected if the ON were unrelated," said Dr. Miller, the Frank B. Walsh Professor of Neuro-Ophthalmology, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore.
"In addition," he said, "there is a much higher incidence of acute ON in the first 6 weeks after the surgery than later, again suggesting a relationship to the surgery itself. There is also an increased incidence of second-eye ON. According to results of the National Institutes of Health-sponsored Ischemic Optic Neuropathy Decompression Trial (IONDT), patients with unilateral NAION have about a 15% to 20% 5-year risk of the same event in a fellow eye; however, cataract extraction seems to increase this risk 3.5 times to a risk of about 50%."
Providing some historic background relating to the risks, Dr. Miller noted that a limited database exists on the subject. Reese and Carroll first brought attention to the problem almost half a century ago when they reported on 17 eyes of 17 patients who had uncomplicated cataract surgery with a normal postoperative visual acuity outcome and IOP. These patients experienced visual loss 6 to 12 weeks after surgery with central scotomas and optic disc swelling unresponsive to systemic steroids.
Ten of those patients had cataract surgery in the fellow eye, and three developed a similar "neuritis."
Fifteen years later, Carroll described nine additional cases. In pooling the data, he found that a total of 17 patients had previous cataract surgery in the fellow eye. Of those 17, eight experienced ON after the first procedure.
"It is from this report that we get the often-quoted risk of about 50% for second-eye involvement when ON developed after first-eye cataract surgery," said Dr. Miller, also a professor of ophthalmology, neurology, and neurosurgery at Johns Hopkins. "However, that risk is derived from patients who underwent mostly intracapsular or extracapsular procedures with large incisions and retrobulbar anesthesia, and it is an open question whether it is applicable in the modern era of cataract surgery."
The concept that two types of postcataract- extraction optic neuritis exist-an immediate event that may be associated with elevated intraoperative IOP and a delayed type that may be more related to the same risk factors as NAION-was first suggested by Michaels and Zugsmith in 1973.
"Judicious control of IOP during surgery may reduce the risk of the immediate type of postcataract-extraction ON. However, there appears to be no way to prevent the delayed event," said Dr. Miller.
More recently, McCulley and colleagues have written a series of articles on this topic. A first publication presented a retrospective analysis of patients from Bascom Palmer Eye Institute who developed ON after cataract surgery. In a cohort study of 5,787 phacoemulsification cases in patients aged at least 50 years and having adequate follow-up, the researchers identified three eyes (0.05%) that developed NAION within 1 year after surgery.
"Although they concluded that the risk is small-only about one in 2,000 cases-they noted it is at least five times higher than the expected incidence in the general population," Dr. Miller said. "That difference suggests postcataract-surgery ON is a real phenomenon and not a chance event."