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Risks to visual health during a total solar eclipse

Solar light can have harmful effects on our vision when observed directly. Although this is unlikely on a normal day, during solar eclipses, it is more probable that we look directly at the sun, exposing ourselves to all the harmful solar radiation and risking our ocular structures. On this occasion, we will delve into the details of this damaging light and discuss how we can protect our eyes from this potential harm.

It is worth mentioning that we are about to witness a total solar eclipse on Monday, April 8, 2024. Mexico has a privileged location for observation.

During a total solar eclipse, the moon comes between the Earth and the sun, casting a shadow that completely darkens the solar disk visible from Earth. This unique phenomenon allows us to appreciate the bright halo of the solar corona and other solar features normally hidden by intense sunlight. However, even during a total solar eclipse, the sunlight continues to emit a full electromagnetic spectrum, ranging from cosmic rays to visible light and other regions of the electromagnetic spectrum. Although our perception is limited to visible light, other wavelengths, such as ultraviolet rays, can be harmful to our tissues, exerting a phototoxic effect on ocular tissues.

Ocular Phototoxicity

Phototoxicity is a phenomenon that can trigger a range of eye diseases, ranging from mild to severe cases, as a result of exposure to light, especially certain wavelengths. In the case of total solar eclipses, the light emitted by the sun can be particularly harmful due to direct and prolonged exposure to ultraviolet rays and other potentially damaging wavelengths. This exposure can have serious consequences for visual health.

During a total solar eclipse, light phototoxicity can cause damage to the photoreceptor cells of the retina by transforming luminous energy into heat or electrical impulses. The electrons generated as a result of this process can become free radicals, highly reactive molecules that can damage neighboring cells and compromise their functionality. This damage can manifest in a range of eye disorders, from eye irritation and blurred vision to more serious conditions such as macular degeneration and glaucoma, which can have long-term consequences for visual health and individual quality of life. That is why ocular protection during a total solar eclipse is fundamental to prevent these risks and preserve our vision in the long term.

How can we protect our eyes?

Phototoxicity is a phenomenon in which exposure to light, especially certain wavelengths, can damage cells in the body. During a total solar eclipse, the light emitted by the sun can be particularly harmful due to direct and prolonged exposure to ultraviolet rays and other potentially damaging wavelengths. This eclipse light can affect the photoreceptor cells of the retina, among other eye structures (cornea, lens, etc.), responsible for capturing light and sending visual signals to the brain.

To properly protect our eyes during a solar eclipse, there are different observation methods, both direct and indirect. Direct methods involve the use of optical filters specifically designed to block harmful sunlight, thus minimizing the risk of ocular damage. These filters are highly effective at selectively absorbing certain harmful wavelengths, such as ultraviolet rays, and reducing solar glare to safe levels for direct observation.

It is crucial to highlight the importance of choosing high-quality optical filters, duly certified by recognized institutions such as the National Aeronautics and Space Administration (NASA) or the American Astronomical Society (AAS), to ensure effective protection during eclipse observation. Using uncertified or lower-quality optical filters can increase the risk of ocular damage and compromise visual health.

In addition to conventional optical filters, it is also relevant to consider other means of ocular protection, such as welding masks. These masks are designed with different shades that reduce the amount of radiation reaching the eyes, providing an additional alternative to protect vision during a solar eclipse. It is worth mentioning that, although not the most recommended practice, it is common in Mexico for astronomy enthusiasts to use shade filters 12 or 16 to observe meteorites.

In addition to optical filters, another protective measure during a solar eclipse is the indirect observation of the astronomical event. This method involves projecting the image of the eclipse onto a surface and observing it safely, avoiding direct exposure to sunlight. Although this approach ensures visual safety, the disadvantage is that it may not fully capture the event's details.

Regarding the advantages and disadvantages of methods for observing a solar eclipse, it is essential to carefully consider each approach. Optical filters provide effective protection by blocking harmful light and allowing direct viewing of the phenomenon. However, it is crucial to ensure the quality and certification of these filters to ensure adequate protection. Indirect observation offers a safe alternative by projecting the eclipse image onto a surface, avoiding direct exposure to sunlight. However, this method may limit the visual experience of the event by missing some details. In summary, both direct and indirect methods have their advantages and disadvantages. The choice will depend on personal preferences and the level of risk one is willing to assume, always prioritizing ocular safety and enjoying the astronomical spectacle responsibly.

It is worth mentioning that at the Faculty of Physical-Mathematical Sciences of the Autonomous University of Sinaloa, we are conducting a study to determine the reduction power of various optical filters for observing the eclipse. Stay tuned for more news about this study, which will contribute to improving our understanding and protection during important astronomical events.


In conclusion, given the imminent total solar eclipse and the potential exposure to ocular phototoxicity, it is essential to consider both direct and indirect observation methods. Understanding the risks associated with solar light during these events requires us to be prudent in protecting our vision.

It is crucial to recognize the importance of preserving our visual health and taking appropriate preventive measures. The use of certified optical filters and indirect eclipse observation are recommended practices to mitigate potential ocular damage. Furthermore, it is important to highlight that Mexico, particularly Mazatlán, Sinaloa, will be a privileged witness to this astronomical phenomenon on April 8, 2024.

Let's prepare for this exciting astronomical event, always remembering to take care of our vision and safely enjoy the majesty of the universe.

Emiliano Teran


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