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Human Body
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spherical shape of the eyeball. It does not interfere with light passing through it. Accommodation
In a camera, the distance between the lens and the film is adjusted until the correct focus is obtained. In the human eye, the distance is fixed. Instead, the curvature (shape) of the lens itself is changed. This adjustment for near and distant vision is called accommodation.
For focussing on a distant object, the lens becomes flatter while to view a nearby object it bulges, becoming more convex. The Pathway of Vision
An optic nerve from each eye passes into the cranial cavity, converge briefly, seperate again after a partial crisscrossing and continue towards the visual area of the cerebral cortex in the occipital lobes of the cerebrum. The images from the left half of the visual field are transmitted entirely to the right hemisphere while those from the right half to the left one. Since there is continual interchange of information between the two hemispheres, a whole image is perceived rather than two halves. Rods and Cones
The retina, the screen on which light rays are projected is a network of two types of light sensitive receptors, rods and cones, There are about 125 million rods and 5.5 million cones. The cones operate in bright daylight while the rods are used for seeing in dim light. Colour Vision
Humans possess the ability to see a full range of colours of the rainbow. White sunlight is a mixture of sever colours called the visible spectrum. The red rays have the longest wave-length while the violet rays are the shortest The human eye can distinguish not only these basic colour: but also more than seventeen thousand intermediate hues.
Colour-blindness occurs when one or more types o cones is absent. In the red-green colour blindness eithe the red or the green cones are missing. It is a hereditar condition and appears far more frequently in males than i: females.
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