The damage caused by light is mainly due to the temperature effect and photochemical reaction caused by its absorption of energy, which causes biological damage. The primary mode of damage depends on the wavelength of light and the tissue exposed. For the hazards of lasers, the main cause of damage is caused by the influence of temperature, and the key parts of the damage are the eyes and skin.
The location of the injury in the eye is directly related to the wavelength of the laser radiation. For laser radiation entering the eyes:
1. Near-ultraviolet wavelengths (UVA) 315-400 nm, most of the radiation is absorbed in the lens of the eye, the effects are delayed, and problems (such as cataracts) may not occur for several years.
2. Far ultraviolet (UVB) 280-315 nm and (UVC) 100-280 nm, most of the radiation is absorbed by the cornea. If high enough doses are absorbed, it can lead to keratoconjunctivitis, so-called snow blindness and weld eye.
3. Most of the visible (400-760 nm) and near-infrared (760-1400 nm) radiation is transmitted to the retina, and overexposure may cause flash blindness or retinal burns and lesions.
4. Far infrared (1400 nm-1 mm) most of the radiation is transmitted to the cornea, overexposure to these wavelengths can cause corneal burns.
Thermal burns (lesions) in the eye are caused when blood flow to the choroid layer, which is located between the retina and the sclera, fails to regulate the thermal load of the retina. Out of range vision is blurred.
Although the retina can repair minor damage, major damage to the macular region of the retina can result in vision or temporary blindness, or even loss of vision. Photochemical damage to the cornea from UV light can lead to photokeratoconjunctivitis (often called welder's flash or snow blindness). This painful condition can last for several days and the person can feel very debilitated. Long-term exposure to UV rays can cause cataracts to form in the lens.
The duration of exposure is also an important cause of eye damage. For example, if the laser is a visible wavelength (400 to 700 nm), the beam power is less than 1.0 mW, and the exposure time is less than 0.25 seconds (anaphobic response time), the retina will not be damaged by prolonged beam exposure. Class 1, 2a, and 2 (see note for laser classification) lasers fall into this category and therefore generally do not cause retinal hazard. Unfortunately, beam or specular observations on Class 3a, 3b or 4 lasers and diffuse reflection from Class 4 lasers can cause such damage due to excessive beam power, in such cases a 0.25 second photophobic response does not Not enough to protect the eyes from injury.
For pulsed lasers, pulse duration also affects the likelihood of eye injury. Pulses with durations less than 1 ms focused on the retina cause acoustic transients that cause severe additional damage and hemorrhage in addition to the expected thermal damage. Today, many pulsed lasers have pulse durations of less than 1 picosecond. The American National Standards Institute's ANSI Z136.1 standard defines the permissible exposure (MPE) that is acceptable to the eye where no eye damage is expected (under specified exposure conditions). If the MPE is exceeded, there may be an increased likelihood of eye injury.
In particular, it should be noted that laser retinal damage can be severe due to the eye's focal length magnification (optical gain) of approximately 100,000 times, as this means that irradiance of 1 mW/cm2 entering the eye will effectively increased to 100 W/cm2
MPORTANT: DO NOT BE DIRECT BY ANY LASER BEAM UNDER ANY CIRCUMSTANCES! In addition, care should be taken to prevent the reflection of the laser beam into the eye, so that the pain caused by eye damage and even the risk of blindness can be avoided.