The safest way to view a solar eclipse
requires the use of proper solar filters. It is imperative that you do not stare at the sun or an individual can risk great damage to the eye even during a relatively short period of time.
Eclipse glasses must have evidence that they comply with the ISO 12312-2
International safety standards for filters for direct viewing of the sun . A reputable vendor is important as there are many counterfeit vendors in the market place. The American Astronomical Society has a list of reputable vendors on their website. The only time it is safe to look at the eclipse is during totality. This will last for only a minute or two minutes. At all other times a safe solar filter must be utilized.
Glasses marked with the IS012312–2 safety standard reduce solar UV and IR radiation. All eclipse glasses and solar viewers must be marked with the international code. You should not be able to see anything but the sun or a comparably bright light through your eclipse glasses . All bright lights should appear dim through your solar viewer. The filters must not be torn,scratched,or punctured in any form. Ordinary sunglasses will not work. Do not make a homemade filter. These homemade filters may dim the brightness of the sun, however your retinas are still at risk of infra red radiation which can damage your eyes permanently.Welding filters of 12 shade or higher may be used.
A simple card projector can also be made quite easily. You will require two stiff pieces of cardboard. To make the pinhole projector a tiny hole is placed in the middle of one of the sheets of cardboard. With your back towards the sun one piece of paper with a pinhole is placed aligned with the second piece of paper. And inverted image of the sun will be projected on the paper screen through the pinhole.
Damage to the eye is caused by solar retinopathy with disruption of the cells in the retina. This is a result of direct solar radiation. The central area of the retina is damaged by eclipse retinopathy. Generally the patient will experience blurred vision, wavy vision, and sometimes headaches. The symptoms are generally in both eyes. Even a short duration of sun exposure of several minutes can lead to significant damage. The degree of initial impairment of vision is important. The better the initial visual acuity the greater the chance of recovery. Some patients will experience permanent blind spots in their central vision. Eclipse retinopathy may last for weeks to months with a result of decreased vision. This deterioration may resolve without treatment. However, some patients experience permanent damage with the loss of central vision. No treatment is currently available.The use of approved eclipse glasses is imperative for the safe viewing of a solar eclipse.