Human eyesight

Man has two kinds of optic nerve cells in his eyes pyramids and bars. The former respond to the brightness and colour of a light, but the latter have no colour sense, and only sense black and white like a monochrome photograph. Almost in the middle of the retina there is a narrow place where only the pyramids concentrate and no bars are found here the sense is sharpest. The greater the distance from this place, the more the density of the pyramids decreases and that of the bars increases. 

A light stimulus against the human eye is different according to the wave length of the light and the kinds of optic nerve cells. Fig.32 shows this relation. 

The degree of stimulus for the bars is the maximum at 5070 A(green), and for the pyramids at 5550 A (yellow green). Thus the sensitivity of the bars and the pyramids is quite different. Accordingly the brightness contrast is more impressive than that of colour in fireworks. The black and white stimulus is about ten times larger than that of colours. 

How does the visibility increase, when the intensity of a light increases For the relationship, we have a rule called Fechner s law. 

Colour blindness only affects a few people in general, but it is said that some kind of the blindness occurs for everyone if the visual angle of the target is very small i.e. not more than 15. This is the situation when we see an object 4.4 meters wide at a distance of 1000 meters. In this case the eyes respond only to red and green and to black and white not to yellow and blue. This is called the third blindness . We are always under the influence of the third blindness, when we see light stars in the far distance. A star which is seen as very poor light green nearby is visible 

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Measurements also commonly involve random errors. These are errors whose size and direction differ from measurement to measurement that is, they are unpredictable and unreproducible. They are commonly associated with the limited sensitivity of instruments, the quality of the scales being read, the degree of control over the environment (temperature, vibration, humidity, and so on), or human frailties (limitations of eyesight, hearing, judgment, and so on). We shall say much more about random error later in this chapter. 

HC1 Permanent human capacities are inadequate (e.g. insufficient strength, height, or eyesight). 

Good vision is an essential requirement for a variety of professions and for many of those, eyesight is expected to be in a perfect condition. This very human sense and its changes could influence the quality of both work and life. The complexity of the... 

The foregoing shows that there is a huge potential in mirror replacement solutions, provided that these solutions are designed ergonomically, or in line with human characteristics. If the system is optimized for human perception and eyesight, it can... 

Stroke is a brain attack that occurs when blood flows to an area of brain is cut off, and it represents a leading cause of disability [1]. This situation causes death of brain cells that are deprived of oxygen. Since a stroke involves brain cells, their death has important consequences on the functions of the human body in particular, functional deficit depends on the brain region affected by dead cells. If the stroke occurs on the right side of the brain, it will affect the left side of the body, including the left side of face. In this case, paralysis on the left side of the body, poor eyesight, quick and inquisitive behavioural style, memory loss can arise too. When the stroke occurs on the left side of the brain, the right side... 

Surry s model focuses on human actions rather than errors and the positive contributions of the operators to safety by adequate handling of hazardous situations. Accidents occur when the demands from the environment to handle hazardous situations exceed the information-processing capacity of the human operator. The operator receives information, processes it, makes decisions and acts. The information thus has to pass through several filters , where there are possibilities of information loss or distortion. There are perceptual filters such as reduced eyesight or hearing or inadequate... 

It is normal and routine for workers to want to be safe on the job. No normal worker leaves home for the workplace with the thought of leaving their fingers, eyesight, scalp, or life at work. Being safe anywhere (including in the workplace) has everything to do with our natural, normal, healthy human desire to survive. And, as pointed out earlier, fear is a survival function. 

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