The eye is a complex and delicate photoreceptor, a comprehensive system for detecting, transmitting, filtering, and amplifying light. The structures of the outer eye, such as the eyebrows, orbits, eyelids, and eyelashes, are the outer barriers that prevent UV rays from entering the inside of the eye. But once the ultraviolet rays reach the eyeball, the layers of the eye itself provide another barrier that ultimately protects the retina.
Although it is said that light is an essential nutrient for the eyes, eating vitamins as a meal can also be poisoning. While we advocate "basking in the sun", we should also pay attention to the necessary protection, not to encourage long-term exposure to the scorching sun, nor to blindly allow the eyeballs to "run naked".
In addition to the UVC, UVB, which is absorbed by the ozone layer, can reach the human eye. Among them, UVB has a shorter wavelength, higher energy, and greater potential biological damage; Whereas, UVA has a longer wavelength and less energy, but is more penetrating. The cornea of the human eye absorbs most of the UVB and some of the UVA, while the lens absorbs the remaining UVB and about half of the UVA, and only a very small amount of UVA eventually reaches the retina. However, it is important to note that the effects and potential harms of UVB and UVA on the structure of the eye are cumulative throughout life, and the associated eye diseases affect millions of people worldwide.
Eyelids: Ultraviolet radiation can cause sunspots on the skin of the eyelids. Excess UVB predisposes to skin cancer, with 10% of skin cancers occurring on the eyelids. Conjunctiva: UVB causes the conjunctiva to produce palpebral fissure plaques and pterygium.
Cornea: Ultraviolet radiation can damage the cornea and cause photodamaged keratitis, which is more severe and typically characterized by "snow blindness". Lens: Long-term UV exposure increases the risk of cataracts. Of the 16 million cases of blindness caused by cataracts, about 3 million have been reported to be due to excess UV radiation.
Retina: Long-term excess UV exposure is a potential risk factor for age-related macular degeneration (AMD). A number of retrospective studies have confirmed this long-term effect and said that it is mainly related to the accumulation of sun exposure in the early years.
Techniques that can help protect the eyes from photodamage caused by UV radiation include sun hats, sunglasses, photochromic glasses, etc.
Sun hat: It can block direct light from above, but its main role is physical sun protection for the face, just taking care of the eyes by the way. In addition, scattered light may be more harmful to the eye than direct light, because the scattered light comes from different directions and cannot be blocked by protection mechanisms that only target direct light.
Sunglasses: Most of the qualified spectacle lenses on the market can provide a certain degree of UV protection, such as crown glass lenses can block ultraviolet radiation below 320nm, CR-39 lenses can block ultraviolet radiation below 355nm, and polycarbonate lenses (PC lenses) can block ultraviolet radiation below 380nm. Sunglasses with a specific UV filter coating on the lenses are able to block almost all UV radiation8 (with UV400 or UV100% marking according to GB39552.1-2020 standard). On the other hand, ordinary sunglasses also greatly reduce the amount of light transmitted, reducing the wearer's vision and visual quality in dark environments.
Photochromic lenses: referred to as photochromic lenses, they can automatically produce corresponding color changes according to the intensity of ultraviolet radiation in the environment through a precise chemical reaction designed. In the absence of a radiation source, such as indoors, the lens appears transparent; If the UV radiation increases gradually, the lens color will also gradually darken. Perhaps the most obvious advantage of a chromic lens is the convenience of being able to adapt to a wide range of light conditions with just one pair of glasses. It can not only achieve all-weather active protection against ultraviolet radiation, but also adapt to the brightness of the surrounding environment to achieve light adjustment, minimize the adverse effects of light intensity, color and contrast, and ensure the comfort and stability of the visual experience.
UV protection for teenagers
UV protection may be more necessary for adolescents than for adults.
The lens of an adolescent is more permeable to ultraviolet radiation than an adult. Studies have shown that the lens of children under the age of 10 is basically transparent, cannot effectively filter ultraviolet rays, and can transmit about 75% of near-ultraviolet radiation (300~400nm), while this value is only 10% for adults over 25 years old. In addition, teens tend to spend more time outdoors than adults. Studies have shown that the total amount of solar radiation received before the age of 18 is equivalent to 50~80% of a person's lifetime. Combined with the cumulative nature of UV radiation, UV exposure at this age will have an impact on susceptibility to related diseases in adulthood.
Another special situation is that many teenagers use low-concentration atropine eye drops to control the rapid growth of myopia, but the pupil dilation effect of the drug may also cause more harmful light radiation to enter the eye. Therefore, for students who use different glasses in a variable environment, but often do not frequently alternate between different glasses, a pair of photochromic lenses that can achieve both refractive correction and adapt to different light environments may be a good choice. As for the stereotype that many parents have that the variable appearance of the color-changing film does not match their subjective perception of the student's image, it may be necessary to give a rational suggestion based on the above objective evidence: let's take off the tinted glasses and re-examine the meaning of the tinted glasses.
In addition to ultraviolet light
Excessive light intensity or light contrast: Generally speaking, the most comfortable brightness range for the human eye is 1000~1400 lumens. However, when it comes to individuals, there are obvious individual differences, and some people are photophobic even under normal light. After ruling out possible diseases, in fact, the fear of light is the same as the fear of itching, which is a person's "personality". In addition, most people will also experience transient photophobia after adapting to a darker environment and suddenly entering a bright environment. No matter which of the above situations, the body is honest, if you are afraid, then find a way to block it. Glare: It is also a condition that seriously affects vision, which refers to the local brightness in the field of vision that exceeds the degree that the eye can adapt to and causes discomfort, and causes a significant decline in visual functions such as vision and contrast, including interference glare, uncomfortable glare and disabling glare. In these cases, wearing a photochromic sheet that automatically adapts to light is a viable solution.
Conclusion: In response to the complex and changeable light environment and the prevention of a variety of potential photodamage, photochromic lenses are a high-quality and efficient vision solution that truly realizes the multi-purpose concept of one lens, which can simultaneously complete the all-round protection of refractive correction, active light management, ultraviolet light and glare, and provide full guarantee for visual quality and visual comfort.
