The risk of losing the eyesight from an accidental exposure to laser radiation is due to the special optical properties of the human eye. When looking at the different depth of
penetration in relation to the wavelengths it can be seen that the eye is transparent only in the wavelength range between 370 and 1400nm.
Effect of different wavelength to the eye
UV-light below 350nm either penetrates 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 – 780nm) penetrates to the retina. The eye is sensitive to radiation and humans have developed natural protective mechanisms. When the light appears too bright, which means the power density exceeds the damage threshold of the eye we automatically turn away and close our eyes (i.e. aversion response or blink reflex). This automatic reaction is effective for radiation up to 1mW power. With higher power levels, too much energy reaches the eye before the blink reflex can respond, which can result in irreversible damage.
The near infrared wavelengths (780 nm– 1400 nm) are a type of radiation that is especially dangerous to the human eye because there is no natural protection against it. The radiation again penetrates to the retina, but the exposure is only noticed after the damage is done. Infrared radiation (1400 nm – 11000 nm) is absorbed at the surface of the eye. It leads to overheating of the tissue and burning, or ablation of the cornea.
