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How to watch an eclipse, safely

March 26, 2024

A solar eclipse will be visible in a path across North America on Monday, April 8, 2024, from Mexico to the US and Canada. This is a rare opportunity to watch the moon block out the sun. After this event, the next total solar eclipse over the U.S. will not happen for another 20 years.

But it’s important to remember that the rays of the sun can be destructive to your vision, so keep your eyes safe when viewing the eclipse with these tips from the National Eye Institute, a part of the National Institutes of Health (NIH) and the largest funder of vision research.

“Watching an eclipse can be fun, but never look directly at the sun. You can seriously damage the retina and even be permanently blinded,” said Chantal Cousineau-Krieger, M.D., a staff ophthalmologist at NEI’s Consult Service. The retina is the light-sensitive tissue in the back of the eye that sends signals to your brain, enabling vision.  

The sun emits high levels of ultraviolet (UV) radiation, which can cause damage to the cells of the eyes' surface and the back of the eye. In addition to UV radiation, the sun also emits infrared radiation, which can generate heat. Direct exposure to intense sunlight can cause thermal damage to the eyes, leading to inflammation, tissue damage, and discomfort.

Electromagnetic spectrum

Both UV and infrared radiation are not visible to the human eye, but can be perceived as heat, which can damage eye tissue. Credit: The National Eye Institute (NEI/NIH)

The main risks associated with watching a solar eclipse (or looking directly at the sun any time) include:

Solar Retinopathy: a condition where the light-sensitive cells in the retina are damaged. This is caused by the sun's intense light, and it can result in a permanent loss of vision. Symptoms include blurred vision, sensitivity to light, dark spots or “blind spots” in your central vision, changes in color perception (or difficulty in distinguishing between colors), or a sensation of pressure in the eye.

It's important to note that the symptoms of solar retinopathy may not appear immediately after sun exposure and can develop gradually over hours or days. In some cases, the symptoms may resolve on their own, but in more severe cases, they may persist or worsen over time.

If you experience any of these symptoms after viewing a solar eclipse or being exposed to intense sunlight, it's essential to seek medical attention from an eye care professional promptly. Early diagnosis and treatment can help prevent further damage to the retina and preserve vision.

Photokeratitis: also known as "sunburned eyes" or "welder's flash," can occur from exposure to intense ultraviolet (UV) radiation from the sun. Symptoms may include pain, redness, tearing, and a feeling of sand in the eyes. While this condition is usually temporary, it can be quite uncomfortable. In some cases, photokeratitis may cause involuntary twitching or spasms of the eyelids (blepharospasm). These spasms may occur as a protective mechanism in response to eye irritation.

Repeated episodes of photokeratitis can increase the risk of long-term eye damage, including cataracts and pterygium, an abnormal growth of tissue on the conjunctiva (the clear membrane that covers the white of the eye) and the cornea (the clear front surface of the eye). If you experience symptoms of photokeratitis after exposure to UV light, it's essential to seek medical attention from an eye care professional for evaluation and treatment.

Macular Edema: Prolonged exposure to the sun, especially during an eclipse, can contribute to macular edema, a condition where the central part of the retina swells, leading to vision distortion and potential permanent damage.

Macular edema can reduce contrast sensitivity, making it challenging to distinguish between objects of similar colors or shades. Colors may appear less vibrant, and details may be harder to discern.

Symptoms of macular edema may also develop gradually over time, and some individuals may not experience noticeable symptoms until the condition progresses. If you experience any changes in your vision, especially central vision, it's essential to see an eye doctor to prevent further vision loss.


Protect your eyes

A solar eclipse can be viewed safely by looking through special-purpose solar filters. These filters must meet an international standard, indicated by ISO 12312-2 certification. They must have the manufacturer’s name and address printed somewhere in the product, and not be older than three years or have any scratches on the lenses.


People wearing approved solar filters

Make sure you pretect your eyes while watching an eclipse. In order, from left to right: Binoculars filters, viewing glasses and cards and ohoto camera filters should always be used for total or partial eclipse viewing. Credit: The American Astronomical Society (AAS)

Never look at the sun through binoculars, photo cameras, telescopes or any optical device using eclipse glasses or handheld filters. The sun will burn through them and damage your eyes. There are special filters that can be attached to the front of optical equipment if you choose to watch the eclipse that way.

“While UV-blocking sunglasses are important to keep your eyes healthy, even very dark glasses cannot protect your eyes from damage caused by looking directly at the sun,” Cousineau-Krieger said. Regular sunglasses, damaged solar filters, or peeking between your fingers or through a pinhole to watch a solar eclipse is not safe.

The only safe way to watch a solar eclipse without a filter is by turning your back to the sun and watching a projection. “Devices such as pinhole projectors allow you to watch an indirect image, which is safe and still exciting,” explained Cousineau-Krieger.

Illustration of a pinhole projector

Using a pinhole projector is a safe and easy way to experience a solar eclipse without the risk of eye damage from direct sunlight. It's suitable for individuals of all ages and requires minimal materials to construct. Image source: NASA