Even the first<unk>  was recognized as being potentially dangerous. Theodore Maiman characterized the first<unk>  as having a power of one "Gillette" as it could burn through one Gillette razor blade. Today, it is accepted that even low-power<unk> s with only a few milliwatts of output power can be hazardous to human eyesight when the beam hits the eye directly or after reflection from a shiny surface. At wavelengths which the cornea and the lens can focus well, the coherence and low divergence of<unk>  light means that it can be focused by the eye into an extremely small spot on the retina, resulting in localized burning and permanent damage in seconds or even less time.<unk> s are usually labeled with a safety class number, which identifies how dangerous the<unk>  is: * Class 1 is inherently safe, usually because the light is contained in an enclosure, for example in CD players. * Class 2 is safe during normal use; the blink reflex of the eye will prevent damage. Usually up to 1 mW power, for example<unk>  pointers. * Class 3R (formerly IIIa)<unk> s are usually up to 5 mW and involve a small risk of eye damage within the time of the blink reflex. Staring into such a beam for several seconds is likely to cause damage to a spot on the retina. * Class 3B<unk> s (5–499 mW) can cause immediate eye damage upon exposure. * Class 4<unk> s (≥ 500 mW) can burn skin, and in some cases, even scattered light from these<unk> s can cause eye and/or skin damage. Many industrial and scientific<unk> s are in this class. The indicated powers are for visible-light, continuous-wave<unk> s. For pulsed<unk> s and invisible wavelengths, other power limits apply. People working with class 3B and class 4<unk> s can protect their eyes with safety goggles which are designed to absorb light of a particular wavelength. Infrared<unk> s with wavelengths longer than about 1.4 micrometers are often referred to as "eye-safe", because the cornea tends to absorb light at these wavelengths, protecting the retina from damage. The label "eye-safe" can be misleading, however, as it applies only to relatively low power continuous wave beams; a high power or Q-switched<unk>  at these wavelengths can burn the cornea, causing severe eye damage, and even moderate power<unk> s can injure the eye.<unk> s can be a hazard to both civil and military aviation, due to the potential to temporarily distract or blind pilots. See<unk> s and aviation safety for more on this topic. Cameras based on charge-coupled devices may actually be more sensitive to<unk>  damage than biological eyes.
Laser
Nd:YAG laser
Comedo extraction
Whitfield's ointment
Oculoplastics
Crusaid
Eyepatch
Contact lens