The extent to which the laser damages the eye is related to the laser of different wavelengths (CO2 laser 10.6 μm; Nd:YAG laser 1.06 μm, He-Ne laser 632.8 nm), and is also related to the total light energy, energy density and power density of the laser entering the eye. Union.
Among the types of lasers, acute damage to the eyes is not caused when the visible or near-infrared laser power density is low. The main reason is that due to the low power density of the laser, the retinal tissue is gradually heated by the laser photon energy, but on the one hand, the heat is transmitted to the surrounding tissue through molecular vibration, and then transmitted to the outside of the eye; on the other hand, the heat can be transmitted. The microvessels that are densely packed in the choroid of the underlying membrane are distributed to the outside of the eye as the blood vessels in the microvessels circulate. Therefore, the temperature of the retina does not increase significantly, or slightly changes in temperature, and is still completely harmless to the eyes.
Retinal damage depends on power and time. For example, when the power density of visible or near-infrared continuous laser increases, the heat accumulation rate on the retina is greater than the heat dissipation speed, or the power density is not very high, but the retinal absorption time is too long, the retina The temperature at which the photon flow is received must be increased, that is, the longer the irradiation time, the higher the temperature rise, and the higher the temperature rise, and more than 10 °C above the normal eye temperature, causing damage to the retina.
1. Pupil size and degree of damage
The size of the pupil has a proportional relationship with the degree of injury. The reduced pupil reduces the amount of laser light entering the fundus. The larger the pupil, the greater the amount of laser light entering the eye, and the more severe the damage to the fundus, the more irreversible. Therefore, the reduction of the pupil has a certain significance in protecting the retina of the fundus and preventing laser beam damage.
2. The pupil changes are different from the environment
In a dark room, the pupils are scattered. In such an environment, if you use a laser, you must carefully protect your eyes. Therefore, the pupil of the eye is outside the maximum state, and although the amount of light entering is small, it is most likely to damage the retina of the eye. The reduced pupil, in addition to reducing the amount of light entering, the amount of laser light outside the pupil can be absorbed by the iris, and the heat is transferred by the microvascular diffusion of the iris. In the eyes of ordinary people, when the dark environment is adapted, the diameter of the pupil is 7-8 mm, which can be reduced to only 1.5 mm under visible strong light, and the diameter of the pupil is usually about 2 to 3 mm during the day. Therefore, the light transmission area between the largest pupil and the smallest pupil is different by more than 20 times.