Eyewire Exclusive: Q&A with Solar Eclipse Expert

Source: Stephen Daily, Executive Editor, News Bryn Mawr Communications

Friday, August 18, 2017 | Medical Studies


With the first total solar eclipse in the United States in 37 years now just days away, millions of Americans will be looking up at the sky to get a glimpse of the rare event. But eclipse experts are warning about the serious damage that can occur to your eyes. Viewing the sun directly, even for brief periods, can cause permanent damage to the retina, and in some cases, result in blindness. The eclipse may also present challenges to the physician community. Both optometrists and ophthalmologists throughout the United States are subject to the possibility of fielding calls from patients who experienced burning or loss of vision from staring at the sun.

To get a better perspective on the type of damage the powerful rays of the sun could have on our eyes, and how eye care practitioners can respond, Eyewiretoday.com spoke with Russell Van Gelder, MD, PhD, chairman of the ophthalmology department at the University of Washington Medical School and the American Academy of Ophthalmology's clinical spokesperson for eclipse viewing safety.

Eyewiretoday.com: On August 21, the first total solar eclipse in 37 years will move across the United States. There will be a lot of people outside looking up at the sun. Could you talk about some of the danger that looking up at the sun can present, and what precautions should people take beforehand?

Dr. Van Gelder: Sure. The radiant energy from the sun has remarkable energy associated with it, and looking straight at the sun, the number of photons that stream through your corneas is probably on the order of 10 rays to the 17th power per second. People intuitively understand this when they take a magnifying glass out to the backyard and burn leaves. As you know it takes only a second or two for that energy of the sun, when it's focused to a single point, to heat up a leaf enough to have it catch on fire.

The optical system of the eye is about the same in terms of total concentration as that magnifying lens. And so if you stare straight at the sun, you're basically focusing that much energy right on the center of the retina—in the fovea—and it's enough that within a few seconds you start to cause photochemical damage to the retina and specifically to the areas around the fovea. And that's why it's so dangerous to look at the partial eclipse. It’s because the photon flux of the sun is the same—it's fewer total photons—but the area where the sun is projecting on the retina is just as intense as looking at the whole sun.

So the real take home message is to never look at the sun during any portion of the eclipse, except totality, if you're in the narrow band of totality, without having on appropriate eye protection.

Eyewiretoday.com: One of the factors that must be considered with this eclipse versus those in the past is that people will be using smartphones to capture a photo of the event. Can you just talk about the danger of using your smartphone and what would you recommend for people who want to take a picture?

Dr. Van Gelder: Yeah, it's going to be a bit of a challenge. There's a couple of issues there. Number 1, you can actually damage your phone's sensor by pointing it at the sun just the same way—you're getting the same concentration of light rays onto a very, very tiny spot on your sensor, and you can burn your sensor. And so I do recommend that people take their eclipse glasses and take a spare pair, cut one of the eyepieces out, and tape that over the camera sensor, if they're going to take pictures.

The real danger in taking pictures is that you're going to be tempted to not wear your own eye protection and point your camera up at the sun, and of course, it's very difficult to exactly block the sun out with your camera while you're looking at an image on the screen. And so in attempting to do that, I would practice on a non-sun object to ensure that if you do this with a light bulb, that you're able to screen your eyes carefully.

The challenge is that the eclipse glasses, if you haven't tried them yet, are extremely dark. They're meant to be extremely dark. They're meant to filter about a million fold of the photons out and as a result, really, unless you're looking directly at the sun with the eclipse glasses on, you're not going to see anything, including your cell phone screen. And that's why it's challenging to take pictures of the eclipse with your cell phone.

Eyewiretoday.com: There's been a lot publicized about the dangers of viewing the eclipse for the general public, but this is also going to be a learning experience for the physician community, whether it be optometrists or ophthalmologists. I’m guessing there is going to be complaints of pain or blurred vision from people who have looked at the eclipse without appropriate protection. Is there anything in general that you could recommend for our physician community who may be getting calls or visits from patients following the eclipse?

Dr. Van Gelder: Yeah, that's a great question, and actually I have not been asked that question before and I've done a few interviews on this now. There was a similar eclipse with a small area of totality and a larger area of partial eclipse in England in 1999. In East Sussex, where the eclipse was, the population is about 500,000 and there were at least 20 people the next day who showed up with demonstrated solar retinopathy from looking at the sun too long. If you extrapolate this, there are about 10 million people who live in the band of totality [in the United States], and probably close to 100 million people who are going to be in at least in some portion of the partial eclipse, and as a result there's a very large population here that's at risk. And if you extrapolate the numbers, as a nation we could be seeing several thousand people with vision loss the day after the eclipse.

Anyone who looks at the sun directly is going to get a temporary scotoma from the bleaching of the rods and cones, and again I would never advise anyone to look directly at the sun, but if you, do you are going to have a hole in the vision for a bit. What happens in solar retinopathy though is that hole doesn't go away, and so people really don't know that they have damage to the retina until the day after the eclipse, when that spot in the vision still hasn't recovered.

For our ophthalmologist and optometrist colleagues, the best way to diagnose acute solar retinopathy is with OCT. And the OCT will show a very characteristic, full-thickness, opacification of the perifoveal and foveal area, which is the early sign of disease. Later in the disease this will progress to a specific loss in the photoreceptor layer, which looks like a little, not really a hole, but a deficit in the normal reflectivity of the outer retina, right in the subfoveal space, and that's essentially a pathognomonic for solar retinopathy for the ophthalmologist or optometrist.

My advice to my colleagues is 1, educate your patients when they're in the office, especially this week, and number 2, be prepared to have some access for these patients, because you're going to see a few on Tuesday after the eclipse, or even Monday night. And to take these complaints seriously and to work these patients up.

Unfortunately, this is such a rare disease, there is no standard treatment right now. No one knows, for example, if corticosteroids will limit solar damage, or if there are other protectants—antioxidants or anything like that—that might be of benefit. And so really there's not much to do except provide some prognosis. About 50% of patients with solar retinopathy will have a substantial recovery of their vision and about 50% won't. And at this point again we don't know who will and won't recover their vision from this. As you said, in the event that only occurs once every 30 to 40 years or so, it’s pretty hard to do prospective randomized control trials on, and so we're really left without much evidence-based medicine on how to treat this.

 


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