ALEX CHADWICK, host:
This is DAY TO DAY. I'm Alex Chadwick.
Coming up, how come the fans don't care about the NBA playoffs this year? Well, some do, but a lot don't.
First, this. There is a report today that federal health officials are concerned about some rare reports of blindness among people who use impotence drugs like Viagra and Cialis. We're joined by Dr. John Kerrison. He is an assistant professor at the Wilmer Eye Institute at Johns Hopkins University in Baltimore, Maryland.
Dr. Kerrison, welcome to the program.
Dr. JOHN KERRISON (Wilmer Eye Institute, Johns Hopkins University): Hey, how's it going?
CHADWICK: I'm well, thank you. But what about these reports? The FDA is investigating, and it notes that it is investigating, I guess, reports of more than 40 instances of a particular kind of blindness. Tell me about this blindness. It's called NAION--am I pronouncing that correctly?
Dr. KERRISON: NAION. Well, we call it N-A-I-O-N. And let me break that down for you. Just forget about the N for now. That's an acronym that stands for anterior ischemic optic neuropathy. And it basically is characterized by sudden, painless, typically unilateral vision loss from damage to the optic nerve. So that's the ON part of it. We think that the mechanism is from a sudden loss of blood flow to the anterior aspect of the optic nerve, so that's where the A and the I--ischemic--stands for loss of blood flow--that's how you have it. Anterior ischemic optic neuropathy.
CHADWICK: And how common is this kind of blindness?
Dr. KERRISON: It's fairly rare form of blindness. I would say that we know a fair amount about the demographics. It typically affects Caucasians in their late 40s and 50s. And the number-one risk factor for developing vision loss from this is having a small optic nerve. And the optic nerve you can think of as like a cable that connects the eye to the brain. And the optic nerve passes through a very small canal as it leaves the eye that we call the scleral canal. Well, people who have this NAION have a very small optic nerve and small scleral canal. And we think that's an essential part of the pathophysiology of this NAION.
CHADWICK: Well, let me ask you this, doctor. There are a reported more than 20 million American men who have taken some of these impotence drugs in the last several years--more than 20 million. Would 42 instances of this rare blindness be a cause of concern in such a large population?
Dr. KERRISON: That's, I guess, a question for the biostatistician, but how do you prove causality when you have an adverse reaction with a medication? Well, first off, there has to be a temporal association, and I believe we have that, between taking the drug and the vision loss. Second, there has to be an absence of some type of alternative cause for it. You know, it may be that before you take Viagra that you should go have an eye exam to make sure that you don't have one of these small optic nerves that put you at risk for it.
CHADWICK: Well, here's the really basic question, Doctor. I don't know if you--you're an eye doctor, so you probably don't prescribe Viagra very often. If you did, would you continue prescribing Viagra for patients, and if you were a patient taking it, would you take it today with this report coming out?
Dr. KERRISON: Well, let me answer the second one--is that if I was a patient, would I take it? I guess I'd probably have to weigh, you know, the benefits vs. the risks here. And the benefit, to me, is kind of an unquantifiable thing, I guess you would say. I have no interest in taking it. But the risk here is an unknown--kind of a black box. So you can either--if you're a really cautious person, I would just not take it. If you want to be a little bit more careful, then, you know--based on the evidence we have, I would look to, you know, be examined, see if I have a small opt--you know, what the doctor said, if I have a--am I at risk for developing this NAION, anyway? And maybe if I had a small disc and I also had hypertension and my blood pressure was prone to volatility, I might even go further to take the Viagra while I was being monitored to see if it affected my blood pressure. And then if I met all those kind of--if I didn't have all those other risk factors, then I might go for it under those conditions.
So on the flip side of it, whether I was a doctor prescribing it, it depends on our level of certainty that this is, you know, a potential adverse affect and adverse reaction. So you might potentially reduce that based on what we know just by doing what I talked about. And at least that way, based on the information that we know, I think you could probably figure out which risk group you're in--if you're in a risk group for developing the vision loss, then not take it.
CHADWICK: Dr. John Kerrison of the Wilmer Eye Institute at Johns Hopkins in Baltimore.
Dr. Kerrison, thanks a lot.
Dr. KERRISON: All right. Take it easy.
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CHADWICK: And there's more coming up on DAY TO DAY from NPR News.
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