The forthcoming total solar eclipse will see people across the US watching the moon obscure the sun – and experts are keen to point out how important it is not to look at the sun directly.
On Monday 21 August, the moon will pass in front of the sun and cast darkness over a 60-mile-wide path across the United States of America, from Oregon through Idaho, Wyoming, Montana, Nebraska, Iowa, Kansas, Missouri, Illinois, Kentucky, Tennessee, Georgia, and North Carolina to South Carolina, from 10:16 PDT to 14:48 EDT.
It's the first total solar eclipse in the US for 99 years, and a once in a lifetime experience for many.
But what actually happens if you look directly at the sun? What do burnt retinas feel like? IBTimes UK asked optician Georgina Kendrick, from the Didsbury Eyecare in Manchester, how to safely watch the solar eclipse – and what happens if you do not do so carefully.
How should you watch the total eclipse safely?
You should never look directly at the sun, even through binoculars or telescopes as the eye can still easily be damaged. The best way to view the solar eclipse is to create a reflected image of the sun either on to a wall or piece of paper.
This can be created using either a mirror or piece of card with a pinhole cut out and, having your back to the sun, place the mirror/card up to a window and allow the image of the sun to be created on a wall opposite. The advantage of this is also that many people can view the eclipse together.
Please note to never look directly into the mirror as this is as bad as looking at the sun directly. There are also eclipse viewing glasses available that include a specialised filter to reduce the sun's rays by 100,000 times.
If you have not got glasses and are tempted just to squint, would that be OK?
No, squinting will not protect the eye from the UV rays and this will damage the eyes.
What about sunglasses?
Even though sunglasses do protect the eyes from UVA and UVB rays, they will not be sufficient from protecting the eyes from looking directly at the sun during the solar eclipse.
What happens to your eyes when you look directly at the sun?
When you look directly at the sun, there are many risks to the health of your eyes. The most painful outcome being corneal sunburn [Photokeratitis], which can cause a very painful eye and loss of vision that can last up to 48 hours. Also, long-term sun exposure from both UVA and UVB rays can cause various problems, including cataracts and macular degeneration. This is due to the eye absorbing the ultraviolet rays, causing damage.
What happens when you burn your retinas? Can you go blind? Does it hurt?
The most common site for a retinal burn to occur would be at the macular, which is a very sensitive area on the retina responsible for our central vision. When this area is damaged by UV rays [from a solar eclipse, for example] it is called solar retinopathy, which may not be painful but the damage can sometimes be permanent. Therefore, leaving you with permanent damage to your central vision.
If you do look directly at it and hurts your eyes, what should you do?
If your eyes are painful following looking at the sun during the solar eclipse, it is advisable to head directly to either your local optician or emergency eye unit to have the eye health checked to ensure no permanent damage has occurred.
Note: This article was updated to coincide with the 21 August 2017 eclipse.