A solar eclipse will occur across the whole of Australia on Thursday morning. It will be most visible in the Ningaloo region of Western Australia. Thousands of people will visit the small coastal town of Exmouth to witness this spectacular event, while Australians elsewhere will experience a partial eclipse.
It is imperative to take steps to protect your eyes from solar retinopathy – permanent eye damage caused by looking at directly at the sun. Expert guidelines advise people to never look at the sun or an eclipse with the naked eye. Any direct viewing should only be done with the correct use of approved solar eclipse glasses that meet an international safety standard known as ISO 12312-2.
Also known as sun blindness, solar retinopathy has been recognised since ancient Greece. It affected astronomers including Sir Isaac Newton, who once used a mirror to look at the sun and saw “afterimages for months”.
Looking too closely
In Turkey in 1976 58 patients sought treatment for eye damage after an eclipse. While some experienced initial improvements, the damage in others was unchanged 15 years later.
In 1999 45 people presented to the eye casualty department of Leicester Royal Infirmary after an eclipse seen there. Retinopathy was confirmed in 40 of them. Seven months later four people could still see “the ghosts of the damage” in their visual field.
And, after the solar eclipse of August 2017, 27 patients in the US state of Utah presented with concerns about vision.
For those people affected by solar retinopathy, the results can be devastating and lifelong.
What happens to your eye when you stare at the sun?
Solar retinopathy is damage to the back of the eye (the fovea centralis in the retina) from exposure to intense light. It is typically caused by sungazing or eclipse viewing but can also result from welding without a shield, looking at laser pointers and from some surgical and photographic lighting.
A process called “phototoxicity” happens when the energy in the light forms damaging free radicals and reacts with oxygen within the retina. This disrupts the retinal pigment epithelium (a layer of supportive cells beneath the retina) as well as the choriocapillaris (blood vessels) beneath.
Fragmentation of the photoreceptors, nerve cells within the retina that detect light and colour, follows and can result in permanent loss of central vision.
Some wavelengths of light that cause solar retinopathy – such as ultraviolet-A radiation and near infrared wavelengths – are not visible to humans, yet cause solar retinopathy in as little as a few seconds. This exposure doesn’t necessarily hurt at the time.
So eclipse gazing – even with little or no visible light and viewed briefly without pain – can lead to loss of vision.
There is no effective treatment
There is no proven treatment for solar retinopathy. Steroid medications have been tried without evidence of success and may make things worse in some patients. Antioxidant medications are used in some eye diseases but there are no studies showing a benefit in cases of solar retinopathy. Vision may improve over time without treatment but many patients are left with residual deficits.
The mainstay of management is therefore prevention.
Five tips for spotting proper eclipse specs
Only approved glasses will absorb the appropriate wavelengths of visible, ultraviolet and infrared light. They must:
1. Be bought from reputable vendors to ensure they are not counterfeits.
2. Display the correct safety certification (ISO 12312-2).
3. Not be scratched, cracked or show any other signs of damage.
4. Fit your face properly so no gaps let light in (check they fit over your usual glasses if you need these to see normally).
5. Be checked by looking at a lamp or light bulb – only light from the sun should be visible through genuine eclipse glasses. This check doesn’t risk eye damage provided the previous steps have been followed.
In Exmouth in WA, the local chamber of commerce and industry has bought some 20,000 eclipse viewing glasses which meet the international ISO safety standard.
Regular sunglasses, welding shields, X-ray film, neutral density filters, red glass filters, mobile phones and homemade sun filters are not safe for viewing the sun or an eclipse.
What if you think the damage is done?
Symptoms to watch out for include blurred vision in one or both eyes within one to two days of exposure.
People may also experience blind spots, altered colour vision, visual distortion (straight lines appearing kinked or wavy), micropsia (objects appearing smaller than normal), light sensitivity and headache. There may be no symptoms at all in the first few hours to a day.
If you have symptoms, abstain from further eclipse viewing. Use dark sunglasses and painkillers (such as paracetamol) for light sensitivity and headaches. Arrange an urgent appointment with an ophthalmologist (or an optometrist, GP or emergency department, who may then refer you to a specialist).
What about totality though?
A total solar eclipse may be viewed without eye protection but only during the brief period while the moon completely covers the sun (the period of totality).
This will only occur over the Ningaloo region, including Exmouth, just before 11.30am (AWST) and last between 54 and 58 seconds, depending on the exact location. The Astronomical Society of Australia has an interactive map which eclipse viewers should visit, to determine the precise timing of totality in their location.
But this still has risks. Eclipse glasses should only be removed after totality has commenced, when the moon has completely covered the sun and it suddenly becomes dark. Just before the sun reappears eclipse glasses must be replaced, to keep observing the remaining partial eclipse.
Remember, totality will only occur over the Ningaloo region, so it is not safe to view the eclipse without protection anywhere else in Australia.
A solar eclipse is a rare occurrence. People will naturally be curious to observe it. Following the right advice will mean they can do it safely.
This article was originally published in the Conversation. Hessom Razavi is an associate professor at the University of Western Australia
