Solar eclipses and your eyes: why sunglasses are not enough and how to watch safely

Every few years a solar eclipse passes over our region, and people head up to rooftops and open spaces and turn their faces to the sky — some relying on their sunglasses, a piece of smoked glass, or the screen of a phone. The problem is that the eye gives its owner no warning here: the retina has no pain receptors, so damage happens silently, and a person only notices it hours later or the next day as a blurred or distorted spot in the centre of their vision. An eclipse is not more dangerous than the sun on an ordinary day, but it tempts people to stare at the sun for a long time — something nobody does on an ordinary day because the glare forces the eyes shut. In this guide we explain what happens to the eye when you look at the sun, why sunglasses fail however dark they are, and which methods are genuinely safe for watching an eclipse, for you and for your children.

What happens inside the eye when you look at the sun?

The lens of the eye works like the magnifying glass children use to focus sunlight onto a piece of paper: it concentrates incoming light into a small point on the retina, specifically on the macula, the area responsible for fine central vision — the part you read with and recognise faces with. When you stare at the sun, a large amount of visible and near-visible light is concentrated on that point, causing photochemical damage to the retinal cells; doctors call this solar retinopathy. During a partial eclipse the sun's disc looks less uncomfortable, so the pupil opens a little wider and the gaze lasts longer, while the uncovered part of the sun is still bright enough to cause harm. The result can be a small blind spot, distortion of straight lines, or reduced sharpness in the centre. Some of it may improve over months, but some remains permanently, and there is no treatment that restores damaged cells.

• Damage without pain: the retina has no sensation, so the absence of pain does not mean your eye is fine.
• Symptoms are delayed: they usually appear hours later or the next day, not while you are looking.
• The centre is what suffers: side vision remains, but reading and making out detail are affected.
• A partial eclipse is deceptive: the disc looks calmer, but its uncovered portion is still harmful.

Why sunglasses do not protect you, however dark they are

Good sunglasses are designed for something specific: to make ambient light on a sunny day comfortable, and to block ultraviolet reflected from roads, sand and water. Even the darkest category of sunglass lens lets through a share of visible light that remains thousands of times more than is safe for looking directly at the sun's disc. Solar viewing filters are an entirely different class: they block the overwhelming majority of visible light along with ultraviolet and infrared, which is why the world through them looks completely black except for the sun itself. Polarised lenses change nothing here, because polarisation cuts glare reflected off surfaces and does not reduce the sun's direct brightness to a safe level. Stacking two pairs of sunglasses does not solve the problem either, and the same goes for smoked glass, X-ray film, CDs, and welding lenses of the wrong shade — all of them either fail to block enough or fail to block infrared, which you cannot see but which heats tissue.

• Not safe: any ordinary or polarised sunglasses, even of the darkest category.
• Not safe: two pairs stacked together, smoked glass, X-ray film, or CDs.
• Not safe: viewing through a phone or camera screen pointed at the sun — you often end up glancing at the sun beside the screen, and the sensor can be damaged.
• Safe: eclipse glasses and filter sheets meeting the ISO 12312-2 standard, or indirect projection.

Safe ways to watch an eclipse

The easiest direct method is eclipse glasses made from solar filters, provided they meet the international ISO 12312-2 standard for filters used to look directly at the sun, and are completely intact, with no scratches, holes, or separation in the film. Test them before the event: indoors you should see almost nothing through them except a very strong lamp, which looks dim. Put them on while looking at the ground, then raise your head towards the sun, then lower your head again before taking them off — never remove them while facing the sun. If you wear prescription glasses, the eclipse glasses go over them, not instead of them. The method that needs nothing bought is indirect projection: a small hole in a piece of card casts an image of the sun onto a white sheet behind it while you keep your back to the sun, and during an eclipse even the dappled shadows under trees turn into lovely little crescents that you can watch with no risk at all. The most dangerous mistake of all is looking through binoculars, a telescope, or a camera lens without a dedicated solar filter fitted to the front, because these devices gather and multiply light — and eclipse glasses worn at the same time are not enough to protect you from light magnified in that way.

• Inspect eclipse glasses before use, and discard any pair that is scratched, punctured, or old and worn.
• Binoculars, telescopes and cameras need a dedicated solar filter on the front, not eclipse glasses on your eyes.
• Pinhole projection onto white paper is free, completely safe, and fun for children.
• In an annular or partial eclipse there is no moment at all when direct viewing is safe.

Children, and what to do if you did look at the sun

Children are at greater risk for two reasons: the lens of their eye is clearer, so it lets more light through to the retina, and their curiosity makes them lift the glasses to “see better”. They therefore need direct supervision the whole time, ideally watching by projection; if they do use eclipse glasses, make sure the glasses stay firmly on their face and that they understand why they must not be lifted. The same applies on ordinary days: a child who dares friends to stare at the sun exposes their eye to the same harm. If you or one of your children did look at the sun without protection, there is no need to panic, but watch for symptoms over the following day: a blurred or dark spot in the centre of vision, straight lines that look wavy, sudden difficulty reading, or washed-out colours in the centre. If any of these appear, see an eye doctor to have the retina examined, and tell them that you looked at the sun and when — that detail shortens the path to diagnosis. Do not reach for drops or home remedies; a medical assessment is the only useful step.

The bottom line is simple: an eclipse is a beautiful event worth watching, and the danger lies not in the sun but in the wrong tool. The sunglasses you wear every day protect your eyes from glare and ultraviolet on the street and the road, but they are not designed for looking at the sun's disc itself, and they never will be, however dark their tint. Use a solar filter that meets the standard or watch by projection, leave magnifying devices to those who have their dedicated filters, and you will keep both the memory and your eyesight.