On April 8, a magical — and rare — celestial phenomenon will be visible from Canada: a total solar eclipse. For many Quebecers, this will be their first chance to observe one. But many are concerned about the risks to the eyes posed by observing the eclipse and schools have preferred to close their doors.
But what are the risks really? The duty spoke with two experts, Dr Langis Michaud, full professor at the School of Optometry at the University of Montreal and Dr.r Ralph Chou, professor emeritus in the School of Optometry and Vision Sciences at the University of Waterloo in Ontario.
1. Is it possible to watch the total eclipse safely?
Yes, answer the two experts without hesitation. With protective glasses specially designed for eclipses, observation is completely safe. It is obviously necessary to ensure that these glasses comply with the ISO 12312-2 standard. They should not be scratched or pierced: even a micro hole in the lens can be problematic, indicates the Dr Langis who also recommends testing your glasses before April 8.
However, children must be well supervised to ensure that they wear the glasses correctly, that is, placed directly in front of and close to the eyes. This way, direct rays of the sun will not reach the eyes, neither from the top of the frames nor from the sides.
The Dr Chou also warns that children should not move around while wearing them — the filters are so dark that nothing can be seen and another danger awaits them: tripping over objects they cannot see. don’t see.
2. Are there other gadgets that make it safe to watch the eclipse?
Sunglasses are prohibited — even those with very dark lenses — as are welder’s visors.
As for those who plan to watch the eclipse through their cell phone camera, they risk… destroying their device. “You can literally burn out the cell phone sensor,” says Dr.r Cabbage. And it also poses a danger to your eyes since you will be looking in the general direction of the sun, adds the Dr Michaud. Special filters for phones can be purchased, but you also need to protect your eyes (with special glasses) in addition to your cell phone, he warns.
Another danger should not be neglected according to him: when we wear protective glasses, we no longer see the screen of our cell phone. So we might be tempted to remove them to take a photo, but this should be avoided during the radiation period.
3. Does the danger exist for the entire duration of the eclipse?
No. The eclipse occurs when the moon gradually moves between the Earth and the Sun. In the total eclipse zone — only in certain sectors of Quebec, including Montreal and Sherbrooke — we will start by seeing a black crescent which will become larger and larger until total darkness. Then the opposite phenomenon will occur and the size of the black crescent will decrease more and more until it completely disappears. It is the periods of “progressive crescent” and “waning crescent” that are dangerous for the eyes. Because during the period of total darkness, it is safe to watch the eclipse with the naked eye. In fact, you have to take off your glasses otherwise you can’t see anything!
If you still see something through the glasses, that means there is still radiation and you should keep them on your nose.
Immediately before and after the period of total darkness, there will be what is called the “diamond ring” effect. It is recommended to put on the special glasses before the progressive crescent zone begins. After total darkness, you have to be very attentive and as soon as you see the “diamond ring”, you have to put your glasses back on “immediately.” »
It is also possible to find the duration of the total eclipse in your area and program an alarm before the end of the period of darkness to remind you to put your glasses back on as quickly as possible, suggests the Dr Michaud.
But for those in partial eclipse zones, danger will be present throughout the celestial phenomenon, says Dr.r Cabbage — and glasses should not be removed.
4. If these instructions are not followed, what are the risks for the eye?
The potential damage will depend on the duration of exposure to the rays. Unfortunately, looking at the eclipse unprotected for a few seconds can be enough to cause eye damage, experts say. And “the more we expose ourselves without protection, the greater the risk we run,” says the Dr Michaud.
But there is no question of automatic blindness here. In many cases observed, the damage was temporary and those affected gradually recovered over the following weeks or months, says Dr.r Cabbage.
Up to 5 or 10 seconds, the risk of permanently damaging one’s eyes is very low, says Dr.r Cabbage, but “not zero risk”. For parents who worry that despite all the supervision, their children will briefly look without the glasses, the Dr Chou tells them: “A few seconds before the child complies with the instructions will not have permanent consequences.” According to the Dr Michaud, a quick glance will “probably not cause a problem, but there is no zero risk.”
5. How do you know if you have damaged your eyesight?
The problem is that we do not know it immediately since there is no sensation of pain on the retina, they indicate. So you don’t have the reflex to look away. And then, the eyes continue to function more or less normally for hours after the damage has been done, explains Dr.r Cabbage. It is often the next day that we realize it: there may be “a spot in the vision”, and everything appears very blurry or very dark.
In their careers, the two specialists have not seen a case of total blindness caused by an eclipse.
Most severe cases that the Dr What we saw were those of young men who observed the eclipse voluntarily, without glasses, or with a telescope whose filter was defective – and not cases of poorly worn glasses or young people who looked furtively.
If in doubt, it is recommended to consult an ophthalmologist or optometrist as soon as possible.