...Some lasers are so powerful that even the diffuse reflection from a surface can be hazardous to the eye.
The coherence and low divergence angle of laser light, aided by focusing from the lens of an eye, can cause laser radiation to be concentrated into an extremely small spot on the retina. ... If the laser is sufficiently powerful, permanent damage can occur within a fraction of a second, literally faster than the blink of an eye. Sufficiently powerful lasers in the visible to near infrared range (400-1400 nm) will penetrate the eyeball and may cause heating of the retina...
... a class 4 laser can burn the skin, or cause devastating and permanent eye damage as a result of direct, diffuse or indirect beam viewing. ...