Non-arteritic anterior ischemic optic neuropathy etiology, approach still unclear

Myriad questions surround the pathophysiology and treatment of NAION, explained Dr. Subramanian, associate professor of ophthalmology, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore.

"There is no consensus yet as to what causes NAION," he said. "Another big question is, When is intervention optimal? Do you have to treat it within 24 hours of the vision loss, or do you have a little time? Finally, the biggest question is, Can we prevent involvement of the fellow eye?"

Indeed, patients who develop NAION are more likely to have typical vasculopathic risk factors, such as hypertension, hyperlipidemia, and diabetes.

Venous disease, however, also is a possible cause of NAION, Dr. Subramanian said.

Underlying risk factors also include sleep apnea and nocturnal hypotension.

Regardless of how patients are treated, data show that visual field will improve in about 25% of patients, although this improvement is usually not dramatic, Dr. Subramanian noted.

Another 41% of patients will have a spontaneous improvement in their visual acuity, and on average, about 15% will have fellow eye involvement in about 5 years, according to data from the Ischemic Optic Neuropathy Decompression Trial (JAMA. 1995;273:625–632).

"Anything we do as far as treatment should [we hope] improve on this natural history, if we're going to expose patients to potentially risky treatments or to those that have side effects," Dr. Subramanian said.

The theory behind steroid use

One of the issues that has emerged in the past few years is the treatment of NAION with corticosteroids, he continued.

"The theory behind this is that NAION, when it starts, may be a compartment syndrome, causing swelling of the axons, which results in further vascular compromise," Dr. Subramanian said. "The cycle builds upon itself. Because steroids reduce edema, we might be able to break that cycle by treating these patients with steroids. That's the theory. If you intervene early, the thinking is that you can prevent damage."

Since the late 1960s, there have been only case reports of the use of oral corticosteroids for the treatment of NAION, and their use has been anecdotal since then.

In a recent case series by researchers at the University of Iowa, 312 of 613 patients were treated with steroids (Hayreh, Graefes, et al. Arch Clin Exp Ophthalmol. 2008;249:1029). The majority started with good vision (20/15 to 20/30), and it did not worsen.

This also was true in the untreated group, however. Upon subgroup analysis, researchers found that patients with 20/70 or worse vision treated within 2 weeks of onset of vision loss did statistically significantly better with treatment versus those without.

Some concerns, however, about this study were raised, including the fact that it was not a randomized trial, investigators were not masked to treatment, and the results were based on analyses that were not originally included in the study protocol, Dr. Subramanian continued.