How to protect your eyes during a solar eclipse

A solar eclipse occurs when the Moon passes between the Earth and the Sun, casting its shadow on the Earth. There are several types of eclipse. In Quebec, the last total solar eclipse took place on April 8, 2024, and the next one will take place in 2106. A total solar eclipse is a rare phenomenon. However, partial solar eclipses do occur periodically in Canada. Consult the dates of upcoming partial solar eclipses in Canada.

Observing the Sun without using protective equipment should be avoided, as it can cause permanent damage to the eyes, even with conventional sun protection such as sunglasses or contact lenses. This risk increases during eclipses, as the Sun's luminosity decreases, reducing the eye's protective reflex.

If you'd like to observe an eclipse, there are safe methods available. Indirect methods are preferable, as the risks are lower than with direct observation.

Indirect observation of an eclipse

There are safe options for observing a solar eclipse indirectly, i.e. without looking squarely at the sun:

• Use a eclipse projector to observe a small image of the sun at the bottom of a closed box. Learn how to build your own projector to watch solar eclipses safely. 
• Observe the shadows as you cross the fingers of one hand over the other and look at the ground. The sunlight passing through the opening in the fingers will project the image of the eclipse onto the ground. To be safe rather than sorry, keep your back to the sun at all times.

Direct observation of an eclipse

People who choose to observe an eclipse directly must protect their eyes at all times by using solar eclipse glasses that comply with the international ISO 12312-2 standard.

Before using certified eyewear, you must

• ensure that they come from a reliable supplier, either directly from the manufacturer or from a recognized distributor.
• check lenses and frames for damage before use.
• note that eclipse glasses can be worn over your regular prescription glasses if they thoroughly cover your eyes.
• ensure that only the sun is visible through the glasses when you are outdoors. If you are indoors, only strong light sources such as the filaments of incandescent lamps or certain LED lamps, such as smartphone flashlights, should be very faintly visible through the glasses.

You can safely pursue day-to-day indoor activities if you avoid looking directly at the sun. It is not safe to watch the eclipse through windows, mirrors, and curtains.

During a solar eclipse, the many mechanisms that normally protect the eye, such as the automatic averting of the gaze, the eyelid closure reflex, and watering of the eyes, are reduced or absent, since the luminosity emitted by the Sun is less powerful.

However, because solar radiation is so intense during an eclipse, it can damage the eye's retina and cause temporary or permanent vision problems. Eye problems can emerge as

• lesions in the retina that cause no pain on exposure, but may prove irreversible. These lesions create a reduction in vision caused by a permanently blurred or dark spot in the middle of the field of vision. They do not appear immediately, but several hours after viewing the Sun.
• lesions in the cornea caused by ultraviolet rays. These painful lacerations lead to a sharp drop in visual acuity and intolerance to light.

In the event of eye symptoms developing in the hours or days following viewing of an eclipse, it is advisable to consult an eye care professional without delay.

Being outdoors during a solar eclipse is not a health hazard if you're not looking directly at the sun. You can enjoy your usual outdoor activities throughout the eclipse.