Current scientific knowledge allows us to know, unlike ancient civilizations, that eclipses are not bad omens nor manifestations of angry gods or monsters devouring the Sun or the Moon. It is a unique spectacle – although it is a frequent and mathematically regular phenomenon – because being able to see it from specific points on the globe is something exceptional. Thus, seeing a total solar eclipse from an exact geographic point occurs only once every 375 or 400 years, on average.
In the Iberian Peninsula, one has not been witnessed since 1912, but now luck (or the manifestation of happy gods) has wanted us to experience several in a row: the total eclipse on August 12, another total one on August 2, 2027, and an annular one on January 26, 2028. Specifically, the one next Wednesday will be seen as total in almost the entire northern half of the peninsula (from west to east across the north of the peninsula, excluding cities like Madrid or Barcelona from that band), while in the southern half it will be seen as partial.
This circumstance should be taken advantage of to observe the phenomenon, but it must be done with the appropriate protection to avoid irreversible eye injuries. In fact, there are multiple documented cases of eye injuries after eclipses throughout history (the first clinical case of solar retinopathy was reported as early as the 17th century). Often people associate that decrease in brightness that occurs during an eclipse with little risk from the sun, but solar radiation remains intense enough to damage the retina. “Precisely that false sense of security can lead to staring for longer and cause irreversible retinal injuries,” explains Andrés Gené Sampedro, president of the General Council of Colleges of Opticians-Optometrists (CGCOO).
Eye damage occurs at the very moment of looking at the sun, but symptoms can take hours or days to manifest and there is no specific treatment to reverse these injuries, so the best way to protect the eyes is prevention. Here are (almost) all possible doubts regarding the eclipse.
Will we be able to observe the sun at any moment without protection?
It will take about 55 minutes until the Sun is completely covered by the Moon and darkness falls. “But it will be very brief: in the central zone, totality barely reaches two minutes (one minute 49 seconds), while in the north and south of the central totality band the viewing time will be shorter,” says Mª Ángela del Castillo Alarcos, director and owner of the School of Sciences-Astronomical Observatory of Titaguas (Valencia), to Science Media Centre (SMC) Spain.
Could we look at the Sun without protection at any of those moments? “The sun emits dangerous radiation even when it is partially covered by the moon. At that moment, high-energy radiation is especially intense and can directly affect ocular structures. The only safe way to observe the total or partial eclipse is to use certified glasses,” emphasizes Jesús Merayo, director of the Fernández-Vega University Institute.
What can happen if the sun is observed without protection? What are the consequences?
“Exposure to the sun can cause a burn and destroy the exposed tissue. This is known for exposure of other tissues such as the skin, but the eye also has a focusing system (cornea and lens) that concentrates the sun’s energy at the point we are looking at and multiplies the thermal effect and the risk of permanent and irreversible damage,” argues the director of the Fernández-Vega University Institute.
Direct observation of the sun can permanently damage the retina and even cause solar retinopathy, an injury caused by photochemical and thermal damage from solar radiation on the macula (where most of the cells that see color or allow us to read are located) that can cause total vision loss. “This risk exists whether looking at the sun unprotected with the naked eye or using inadequate methods,” adds Merayo.
Which parts of the eye are most affected if the eclipse is viewed without protection?
Damage to the retina is the most common if the eyes are not properly protected. It affects a very small but important part of the retina called the macula. This damage may go unnoticed at the time of exposure because the retina “barely has pain receptors, which causes many not to associate symptoms with eclipse exposure,” points out Merayo.
Other injuries from sun exposure can damage ocular tissues such as the skin of the eyelids, the cornea, and the conjunctiva, which also require prevention and treatment. For example, it can cause photokeratitis, a corneal burn that manifests hours later with pain, stinging, itching, redness, tearing, and great discomfort with light.
Can the eclipse be observed through telescopes, binoculars, cameras, or mobile phones?
According to Marcos Pérez Maldonado, director of the Coruña Scientific Museums, one must avoid using telescopes or binoculars “unless you have the necessary filters and experience in solar observation,” in statements to SMC Spain. For this reason, Merayo does not recommend it in principle, “since we have no evidence that cameras, mobile phones, or optical instruments have adequate filters for sun exposure. To avoid damage to the sensor, photography or astronomy enthusiasts are used to protecting these optical instruments, including their lenses, with filters and protectors. But this is not the case for the general population. Therefore, the best recommendation is to protect the eyes with certified glasses.”
What type of glasses are recommended?
The only safe way to observe the total or partial eclipse is to use certified glasses that comply with ISO 12312-2:2015. Some common mistakes that can cause irreversible retinal injuries should be avoided, such as using conventional sunglasses; homemade methods like X-rays, photographic negatives, CDs or DVDs, ski goggles, smoked glass, or improvised filters; “or using optical instruments only with eclipse glasses, since these are not designed to withstand the concentrated light from magnification systems,” indicates the director of the Fernández-Vega University Institute. The specialist emphasizes that many of these methods “reduce glare and create a false sense of security, but do not block radiation that can cause permanent retinal damage.”
The specialist recommends checking that the filter has no scratches, perforations, or any other damage. “In the case of children, eclipse observation should always be done under adult supervision who can check the correct use of certified glasses,” he stresses.
Is there a recommended time to observe the phenomenon?
“Observation of the phenomenon should be brief, in intervals not exceeding 30 seconds, alternating with breaks,” advises Merayo. Although many astronomy or astrophysics specialists recommend looking at the Sun unprotected during the seconds that the totality phase of the eclipse lasts (remember, not throughout all of Spain), ophthalmologists discourage this because it is only a few seconds and since there is no pain felt in the retina, the observation time might be prolonged causing damage we do not perceive. “Although theoretically during the total eclipse period when it is completely dark the glasses could be removed, it is not recommended because they would have to be put back on when the first bright edge appears. If we have children in our care, we must ensure they have protection properly worn at all times,” Merayo adds.
How can you tell if the retina has been damaged? What would be noticed if that happens?
After following protection recommendations, retinal damage should not occur, considers Merayo, who recalls that damage in patients with solar retinopathy can generally go unnoticed at the time of exposure because the retina barely has pain receptors and many do not associate symptoms with sun exposure.
The most frequent symptoms are blurred vision, the appearance of a central spot (like a dark or blurry point in the center of vision), distortion of lines (seeing waves), and difficulty reading, distinguishing colors, or focusing on details. “If any of these symptoms occur, it is recommended to see an ophthalmologist as soon as possible for better evaluation. In any case, prevention is the best option, as injuries can be irreversible,” concludes Merayo.
What other recommendations should be followed?
Apart from the visual aspect, there are other precautions to take to watch the eclipse. The Spanish Society of Emergency Medicine (Semes) recommends choosing a safe place, “away from difficult access areas, ravines, or areas at risk of fire“; not stopping the vehicle on shoulders or unauthorized places to watch the eclipse; and maintaining attention while driving and avoiding distractions related to observing the phenomenon.
Likewise, considering also respiratory diseases preventable by vaccination (whose transmission is favored in mass events), vector-borne diseases (mosquitoes and ticks), sexually transmitted infections, alcohol, tobacco, and psychoactive substances/drugs consumption, food safety, or sun exposure and rising temperatures.
Regarding the latter, Semes recommends maintaining proper hydration throughout the day; using a cap or hat, light clothing, and sunscreen if staying outdoors for several hours; seeking shaded areas whenever possible during the wait; paying special attention to children, the elderly, pregnant women, and people with chronic diseases; and seeking medical assistance if symptoms compatible with heat stroke occur, such as intense dizziness, disorientation, loss of consciousness, or elevated body temperature.
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