The above table shows the depth of penetration of electro-magnetic radiation in the human eye.
The risk of losing ones eyesight through laser radiation, is due to the special optical properties of the human eye. When we look at the different depths of penetration in relation to the wavelengths, we can see that the eye is transparent only in the wavelength range between 370 and 1400 nm.
UV-light below 350 nm advances to the lens or is absorbed at the surface of the eye. A consequence of exposure to high power light at these wavelengths, is an injury to the cornea by ablation or a cataract.
Light in the visible wavelength region (380 - 780 nm) advances to the retina. The eye is sensitive to radiation and humans have developed natural protective mechanisms. When the light seems too bright, which means the power density exceeds a damage threshold of the eye, we automatically turn away and close our eyes (blink reflex). This automatic reaction is effective for radiation up to 1 mW power. With higher powers, too much energy reaches the eye before the blink reflex can work, with the resulting consequence of irreversible damage.
The near infrared wavelengths (780 - 1400 nm) are a type of radiation that is especially dangerous to the human eye. Humans do not have a natural protection against it. The radiation advances to the retina, but the exposure is only noticed when the damage is done.
Infrared radiation (1400-11000 nm) is absorbed at the surface of the eye. It leads to overheating of tissue and burning, or ablation of the cornea.
