The flashing light beam at the concert forms different shapes and even characters in the night sky through color change. At night, in the square of the city, there are constantly beams of colorful light emitting from the ground to the sky, adding gorgeous colors to the beautiful night. These charming lights are lasers.
Laser is a kind of monochrome highly concentrated light with good monochrome and directivity, so it can bring us dazzling and colorful brilliance.
However, it is also because of this that the safety of lasers is also being questioned, especially whether toy lasers harm children’s eyesight, which is a concern of parents. Recently, a WeChat popular in WeChat circle of friends: a glance at a laser pointer may cause permanent blindness.
Many friends ask: Teachers in children’s schools use laser pens in class. Is it possible to cause damage to children’s eyesight or even permanent blindness?
Visible light lasers can indeed cause visual damage.
The most commonly used laser in daily life belongs to visible light laser. After high-intensity visible light or near-infrared light enters the eye, it will pass through the refractive system of the eye and accumulate on the retina.
If the laser power is relatively high, A large amount of light energy is instantaneously concentrated on the retina, and the retinal pigment epithelium will absorb the energy and cause the temperature of the photoreceptor cell layer of the retina to rise rapidly, so that the photoreceptor cells will coagulate, degenerate and necrosis and lose the photosensitive function. The coagulation and degeneration of proteins caused by this heat will eventually cause irreversible damage to visual function.
However, if the power is low and the irradiation time is short, the heat generated by the light will disperse by itself without causing damage to photosensitive cells.
Damage is related to wavelength, power and irradiation time.
The degree of laser damage to retina depends on the laser wavelength (color), power, irradiation time, fundus pigment, pupil size and, most importantly, the irradiation position.
If we look directly at the laser beam, the laser beam will focus directly on the macular area. Although the macular area accounts for only a small part of the total retina area and the fovea diameter is only about 0.5 mm, it is the place where we have the most acute vision and the only place where we can see objects clearly.
However, the fovea of the macula of the retina has no blood vessels and nerves distributed, and its heat diffusion function is very poor. Once damaged, there is little hope of repair. It can be said that the fovea is the weakest part of the retina and is more vulnerable to damage than other parts of the retina after being subjected to laser action, so direct laser exposure to the eye is very dangerous.
Clinically, we occasionally encounter the macular spot directly irradiated by a laser pointer during play. Resulting in the atrophy of photoreceptor cells in the macular region, As a result, children with significantly reduced central vision. In 2013, the Chinese Journal of Ophthalmology published a case report from Beijing Tongren Hospital. A 12-year-old boy was playing with a laser pointer in front of a mirror and was accidentally hit by reflected laser light in both eyes. As a result, central black spots appeared in both eyes and corrected vision decreased to below 0.4. Optical tomography showed that the nuclear layer of photoreceptor cells in macular region disappeared with effusion or blood accumulation.
This vision loss is usually permanent and irreversible.
Laser pointer should not be used as children’s toy.
At present, there is no mandatory power limit and warning for laser pens (toys) sold on the market. Children can also buy all kinds of high-power laser toys at will, which is an important hidden danger causing visual damage to children.
According to the classification standards of the U.S. Food and Drug Administration (FDA), only Class I laser pens (or similar laser devices) are safe, and permanent and difficult-to-remove labels must be affixed from Class II (with a power of 1 mW) to remind users not to stare at the light.
FDA suggests that general household laser pens must be strictly controlled at the level of I to II A. It is not suitable to be used as children’s toys. Parents should publicize relevant knowledge of laser radiation hazards to children and teach children to avoid looking directly at lasers.
For office or teaching laser pens, they should choose to purchase products that meet national safety standards and should be placed out of reach of children.
Not all lasers are detrimental to vision
Since laser may cause irreversible damage to vision, why is laser often used in ophthalmic treatment to prevent glaucoma or correct myopia? This is because different kinds of lasers will produce different physical reactions in human tissues to achieve therapeutic effects.
YAG laser is a special kind of invisible laser to prevent the acute attack of glaucoma. A special switch is used to intercept a section of laser energy and act on the iris to generate micro-explosion, thus forming holes in the iris. However, this energy is very limited and will not affect the lens several millimeters away from the explosion point, and has no effect on the retina about 20 mm away.
Excimer laser commonly used in the treatment of myopia has very low energy, which can just break the molecular bonds connected between molecules and vaporize corneal tissue, thus achieving the therapeutic purpose.
When laser is used to treat retinal choroidal lesions, retinal vein embolism and other lesions, Although the laser irradiating the retina is also visible light laser, Doctors will control the laser to irradiate the retina far away from the macular region for a short time and with low energy. Although the photoreceptor cells of the retina irradiated by the laser will degenerate and atrophy, the death of these photoreceptor cells will generally not affect our central vision, and the purpose of treatment can be understood as sacrificing [local] vision to protect [central] vision.
All kinds of lasers used in medical treatment to treat ophthalmic diseases are safe to the patient’s eyesight as long as they conform to the standard operating procedures, and everyone need not stop eating because of choking.
Author: Mao Jin
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