Things you need to know when buying sunglasses

In the Middle East countries, including the Sultanate of Oman, it is common to be exposed to the sun all year round. The sun is the main source of ultraviolet rays, as it emits long ultraviolet waves and medium waves, both of which are considered harmful. Long UVs can cause the skin to age, while exposure to medium UVs can cause sunburn.

Ultraviolet rays are a form of energy similar to visible light or X-rays that can cause damage to the skin and eyes. They peak in the middle of the day and during the peak summer months. They get stronger near the equator, and may cause the development of small, irritating vessels in the white part of the eye, such as pterygium and septum, especially in people who spend a long time in the midday sun, such as surfers, fishermen and farmers. These cases may require surgical intervention to remove the growing vessels.

Therefore, it is important for those living in sunny areas to protect the eyes while being in the sun to help prevent pterygium and sebaceous infections and also reduce the risk of developing more serious health conditions, such as lens and eyelid cancer. Experts advise wearing UV-blocking sunglasses and making sure that the label on the glasses indicates 100 per cent UVA protection, or protection from all UV400 rays.

In a thread of tweets, Hisham al Abri, an ophthalmologist, said that sunglasses are necessary to protect eyes from the sun, and he gave some tricks that are useful when buying glasses.

“It is important to look for a sign or a phrase that says that it blocks 100 per cent of sunlight. The quality of the lenses in glasses without a prescription can be confirmed by looking at a surface with squares such as floor tiles. Put the glasses at an appropriate distance from your face and cover one of your eyes. Move the glasses in the directions and observe the lines through the lens. If you notice the lines are straight, the glasses are good. If not, it is better to change it”.

Al Abri pointed out that most of the glasses in the market are made of plastic, so they are easy to scratch. It is best to take into account that the glasses are scratch resistant coatings. He advised, “use polarised glasses, which block the rays reflected from surfaces, such as mirages on the street and the rays reflected from the surface of the water,” explaining that this feature is now found in most cars in their windshield, in addition to being available in the material that is used to block ultraviolet rays.

The ophthalmologist said that the opacity of the lens has nothing to do with blocking ultraviolet rays, as the medium opacity in the glasses is usually sufficient unless the person works in a high brightness area. "The opacity of the lens is equal or gradual, so that it is darker at the top and lighter at the bottom. This is suitable for driving because it reduces the brightness of the sun while allowing a clearer view of the street."

There is, however, another opposite type (lighter at the top and darker at the bottom) which is suitable in snowy areas. The third type, in which the opacity is more at the top and bottom but less in the middle, is not recommended for driving and is more suitable for athletes.

Al Abri said that some lenses are coated with some metals to be reflective, so do not assume that this type protects against ultraviolet rays if it is not written on it. “In general, this type reduces the amount of light that reaches the eye because it reflects some of it.” He explained.

Also, some glasses block blue rays, but it has not been scientifically proven whether these blue rays are harmful to the eyes or not. “Anyhow, this type of glasses is useful for looking at distant things in the time of snow and fog, so they are used by hunters and skiers”.

He recommended glasses that cover the largest area of the eye because they block ultraviolet rays more, pointing out that “there are companies that promote their glasses as blockers for infrared rays, knowing that this type of rays does not harm the eyes”.

“The price does not mean the quality. Cheap glasses, which have 100 per cent protection from UV rays, are better than world-class designer glasses without UV400 protection. With all these features, the glasses do not protect you from the rays emitted by arc welding, tanning devices and snowy areas. These types need special filters that are not available in ordinary glasses”, he concluded.