Human body vision

The sense of hearing is a fragile and vital function of the human body. It is similar to vision, more so than the other senses, because permanent and complete damage can be sustained quite commonly in an industrial environment. So it follows that noise pollution has been recognized as a safety concern for a long time, and has been appropriately regulated. 

Note that even bodies at liquid-air temperatures emit photons between 10 and 100 microns in wavelength, l.e.- 100,000 and 10 A in wavelength. The earth itself at a temperature of 300 °K. has an emission between out 20,000 and 300,000 A in wavelength, i.e.- 2000 nm. and 30,000 nm. What this means is that even you emit infra-red wavelengths as a consequence of being warm. Note that this is the basis of "night-vision" headgear which can detect human bodies even when it is so dark that other objects are invisible to the naked eye. 

Radiation emitted from the human body and warm objects is mostly infrared, which is detected by burglar alarms, military night-vision scopes, and similar equipment. 

Vitamin A is a vitamin found in certain animal fats, such as halibut liver oil or butter, and necessary for growth and vision of animals and the health of epithelial structures. Two forms of vitamin A are known, and there are several forms of yellow plant pigments, the carotenoids, from which the human body can make vitamin A to a variable extent. 

Implantable medical devices have been widely used to restore body functions, improve the quality of life, or save lives. Experts estimate that 8 to 10 percent of all Americans (some 20 million to 25 million people) [1], or about 1 in 17 people in industrialized countries [2], carry some form of implanted device. Many medical devices, such as the implantable cardiac defibrillator, cochlear implant, artificial vision prosthesis, neuromuscular microstimulator, and the like contain sophisticated electronic circuits. Such long-term implantable medical devices are susceptible to damage by body fluids over time. Hermetic packaging is required to protect the electronic circuitry of the implant from the harsh environment of the human body. 

Beyond visible light lies infrared (IR) radiation. The heat you feel when you place your hand near a hot object is infrared radiation. All warm objects, including human bodies, emit infrared light. Although infrared hght is invisible to our eyes, infrared sensors can detect it and are often employed in night vision technology to help people see in the dark. 

Vision is vital for human activities, and eyes are very sensitive to a number of toxic insults induced by chemical compounds. The most serious outcome is permanent eye damage which may be so severe as to cause loss of vision. The eye consists of the cornea and conjunctiva, the choroid, the iris, and the ciliary body. It also contains the retina, which is of neural origin, and the optic nerve. The retina contains photoreceptors, a highly specific light-sensitive type of neural tissue. The eye also contains the lens and a small cerebrospinal fluid system, the aqueous humor system, that is important for the maintenance of the steady state of hydration of the lens and thus the transparency of the eye. 

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