Due to the nature of the laser, can make the energy concentration in space and time. Formed by the refractive media focused on the retina of the eye image, and make the energy density of the retina is the cornea on the incident energy density increase from 104 to 105; Good monochromaticity, laser in the fundus of the color difference is small. The characteristics of the low laser energy irradiation can cause corneal or retinal damage.