The flashing beams of light at concerts form different shapes and even words in the night sky through color changes; the squares in the city at night constantly have the ground firing beams of colorful light into the sky, adding life to the beautiful night. These fascinating rays are lasers.
Laser is a monochromatic highly aggregated light, with good monochromatic, directional, etc., so it can give us a dazzling colorful light.
But because of this, the safety of lasers is also being questioned, especially whether toy lasers are harmful to children’s eyesight, is a concern for parents. Recently, the WeChat circle of friends a WeChat popular: a glance at the laser pointer may cause permanent blindness.
Many friends consulting: children in school classes are using the laser pointer, whether it is also possible to cause damage to children’s eyesight or even permanent blindness?
Visible laser light can indeed cause vision damage
The most commonly used lasers in daily life are visible lasers. When visible light or near-infrared light of high intensity enters the eye, it passes through the refractive system of the eye and accumulates on the retina.
If the power of the laser is high, a large amount of light energy will be concentrated on the retina in an instant, and the retinal pigment epithelium will absorb the energy, resulting in a rapid increase in the temperature of the photoreceptor cell layer of the retina, so that the photoreceptor cells will coagulate, degenerate, necrotize, and lose their photoreceptor function. This heat-induced protein coagulation and degeneration eventually causes irreversible damage to visual function.
However, if the power is low and the irradiation time is short, the heat generated by the light will dissipate on its own without causing damage to the photoreceptor cells.
Damage is related to wavelength, power and exposure time
The extent of laser damage to the retina depends on the wavelength (color) of the laser, the power, the duration of exposure, the amount of pigment in the fundus, the size of the pupil, and most importantly, the location of the exposure.
If we look directly at the laser beam, the laser beam will be focused directly on the macula. Although the area of macula only accounts for a very small part of the total retinal area, and the central concave diameter is only about 0.5mm, it is the place where our vision is the sharpest, and it is the only part where we can see objects clearly.
The central recess of the retinal macula has no blood vessels or nerve distribution, and the heat diffusion function is very poor, so once it is damaged, there is little hope for repair.
It can be said that the central recess is the weakest part of the retina, which is more vulnerable to damage than other parts of the retina after being exposed to laser light, making direct laser light on the eye very dangerous.
We also occasionally encounter children in the clinic who are exposed to direct laser pointer light on the macula during play, resulting in atrophy of photoreceptor cells in the macula, which leads to significant loss of central vision.
In 2013, the Chinese Journal of Ophthalmology published a case report from Tongren Hospital in Beijing. A 12-year-old boy playing with a laser pointer in front of a mirror was accidentally exposed to reflected laser light in both eyes, resulting in central black spots in both eyes and a decrease in corrected visual acuity to below 0.4. An optical tomography scan showed loss of the nuclear layer of photoreceptor cells in the macula with fluid or blood accumulation. This vision loss, however, is usually permanent and irreversible.
Laser pointer should not be used as a toy
The laser pointer (toy) currently on the market does not have mandatory power limits and warnings, and a variety of high-powered laser toys can be purchased at will by children, which is an important potential hazard that causes vision damage in children.
According to the U.S. Food and Drug Administration (FDA) classification standards, only Class I laser pointer (or similar laser devices) is safe, and from Class II (power up to 1mW) must be affixed with a permanent, not easy to remove the label to remind users of the attention of the light is strictly prohibited to stare at.
FDA recommends that the general household laser pointer, must be strictly controlled at the level of Ⅰ to ⅡA. Laser pointer should not be used as a children’s toy, parents should promote the relevant knowledge of laser radiation hazards to children, and teach children to avoid looking directly at the laser.
Office or teaching laser pointer, should choose to buy products that meet national safety standards, and should be placed out of reach of children.
Not all lasers are harmful to vision
Since lasers can cause irreversible damage to vision, why are they often used in ophthalmic treatment to irradiate the retina, prevent glaucoma or correct myopia?
This is because different types of lasers produce different physicochemical reactions in human tissue to achieve therapeutic effects.
For example, the “YAG laser” is used to prevent acute attacks of glaucoma. This is a special invisible laser that intercepts a section of laser energy through a special switch and acts on the iris to produce a “micro-burst” effect, thus creating a hole in the iris and lowering the eye pressure. However, this energy is very limited and does not affect the lens, which is only a few millimeters away from the blast point, and has no effect on the retina, which is about 20 mm away.
Another example is the “excimer laser” commonly used to treat myopia. It has a very low energy, just enough to break the molecular bonds that connect molecules to each other and vaporize the corneal tissue so that it can be sucked away for treatment purposes.
In addition, in laser treatment of retinal choroidopathy, retinal vein embolism and other lesions, the laser that irradiates the retina is also a visible laser, but the doctor controls the laser to irradiate the retina away from the macula for a very short period of time and at a low energy. Although the photoreceptor cells of the laser-irradiated retina may become degenerative and atrophied, the death of these photoreceptor cells does not generally affect our “central vision”, and the purpose of the treatment can be interpreted as sacrificing “local” vision to protect “central” vision.
As long as the various lasers used in medical treatment of ophthalmic disorders are in accordance with standard operating procedures, they are safe for the patient’s vision, so there is no need to choke on them.