Know the best sunglasses

According to the Fars news agency’s health reporter, the main feature of good sunglasses is that, in addition to being beautiful and stylish, it protects the eyes from harmful ultraviolet rays; This means that a good pair of sunglasses should be the best protection against ultraviolet (UV) rays.

Almost all of us are well aware of the harmful effects of ultraviolet rays on the skin, but some people may not know that ultraviolet rays can cause destructive damage to human eyes.

Long-term exposure to radiation can lead to eye disorders such as cataracts, snow blindness, and skin cancer. Even short-term exposure or reflections can burn the front surface of your eyes. A good standard pair of sunglasses can block 99-100% of UVA and UVB rays.

The World Sunglasses Day ceremony is held every year on June 27 to remind everyone of the importance of using UV protection on sunglasses. Therefore, by constantly using sunglasses and protecting your eyes from the ultraviolet rays of the sun, every day is actually sunglasses day, and the misconception that these glasses are summer will disappear, this is exactly the philosophy of naming and celebrating this day.

Mohammad Ali Javadi, eye specialist He said: The cause of vision is the return of light from objects and its perception by the vision center in the brain, and seeing is achieved by visible waves. Also, sunlight is a set of visible and invisible waves, the wavelengths between 400-700 nm are visible light and the wavelengths shorter and longer than this range are invisible waves. The wavelength of light between 200-400 nm is considered as ultraviolet waves, which are divided into types A, B and C. Type B is harmful to the skin and eyes and has more radiation in the summer season. A small amount of exposure to ultraviolet rays is necessary for the production of vitamin D, but long-term exposure is harmful to the eyes.

Javadi added: Since sunglasses absorb up to 100% of ultraviolet rays, it is necessary to use sunglasses and, to some extent, brimmed hats to prevent damage from ultraviolet waves.

According to him, the creation of pterygium, the creation of cataracts, damage to the cornea, especially when skiing on snow and water, damage to the macula, which are mainly caused by infrared waves, are among the damages that invisible waves cause to the ultraviolet type B cornea.

Shahid Beheshti University of Medical Sciences faculty member stated that sunglasses are a type of glasses that absorb a lot of sunlight and completely absorb the harmful rays of sunlight, especially ultraviolet rays, and said: the amount of sunlight in any environment, It is measured in units of candela per square meter (2cd/m). The minimum amount of light required for normal vision is 2cd/m 350, but up to 2cd/m 2000, the human eye is comfortable and does not feel dazzled or tired.

He said: In many outdoor environments, the amount of light is much more than this amount. For example, the amount of ambient light on a sunny day under the sun is 2cd/m 4000-7000. The reflection of the sun on the snow creates an intensity of 15,000-30,000 cd/m. Likewise, the amount of light on a sunny beach is 6000-15000, the amount of light reflected from the asphalt surface is 3000-9000, the amount of light in the shade of trees is 300-600, and in the blue sky away from the sun, 300-600 candela per square meter.

Javadi continued: In terms of visible light, sunglasses have two features: light transmission rate and color. Standard sunglasses usually let 15-25% of the light through, which is enough for most everyday activities. In the shade, the amount of light that can be seen with these glasses; It is about 2cd/m 60, which is still enough to see. Of course, for certain activities that are carried out in very bright environments; Darker glasses are required. These activities include winter sports such as skiing and snow-climbing, especially at high altitudes, flying high above the clouds, and activities that take place in intense summer sunlight for long hours. For such environments, glasses that transmit only 8-12% of light are needed, and sometimes glasses that transmit 3-5% of light are used.

This cornea specialist added: The best color for sunglasses is gray, which does not change the color of objects and surroundings for the user despite reducing the light. Brown and green sunglasses are also used. Brown glasses reduce the blue light of the sky and increase sensitivity to contrast, which are favorable for long drives. In general, the best color for sunglasses is gray first and then brown.

Javadi summarized the general characteristics of a good pair of sunglasses below:

1- The darkness of sunglasses should be such that a person is comfortable with them in the sunlight and does not get dazzled.

2- When we shake sunglasses in front of a patterned screen; The page should not be seen as wavy, blurred, crooked and distorted.

3- Sunglasses should not disturb the recognition of the colors of objects and traffic lights. The gray color of the glasses is preferable in this regard.

4- The glasses should be impact resistant. Polycarbonate is the most resistant of all.

5- It is necessary for glasses to absorb UV rays.

6- The sunglasses frame should be big to provide enough protection.

According to him, a simple rule to understand the suitability of the darkness of the glasses is that when we look in the mirror with glasses in a room with normal light; Do not see your eyes. The maximum amount of light passing between 15 and 25% is suitable; That is, the glasses should absorb or reflect 75-85% of the light.

The academic staff member of Shahid Beheshti University of Medical Sciences added: The only type of glass that reduces the strong reflection of light from some surfaces or points of objects; The glass is polarized. The light reflected from the rear window of cars, the door of the trunk of cars, the surface of water and the surface of some roads and the like, are polarized in the horizontal plane, and these glasses, which have vertical polarization; Removes horizontal polarized light. Polarized glasses are used for all kinds of purposes, especially driving, fishing, all kinds of sea sports and the like.

He stated that the high price of sunglasses is not a criterion of better quality, and continued: If the sunglasses are not standard, they may be harmful. Also, if the amount of absorption of ultraviolet rays is not enough, by creating darkness in front of the eye, it causes the pupil to dilate and as a result, the amount of light entering the eye increases.

In the end, Javadi reminded: the probability of children’s eyes being damaged by UV rays is higher than that of adults, because the lens of their eyes is more transparent than that of adults, and also their pupils are wider than adults, and as a result, more radiation enters their eyes, but Care should be taken not to provide them with non-standard glasses.

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