The Human Eye:

The Eye is an  organ  that is used for seeing,  it provides vision. The eyes are a set of complex optical organ of impulsive force that detects light which is then converted into electro-chemical neurons. It collects light from the surrounding environment and then controls its intensity, through a diaphram that adjusts and assemble its lenses to form an image.



Inside the eye form groups of electrical signals which is then transmitted to the brain, from the neural pathways. These pathways connect the eyes via an optical nerve to the cortex and throughout the brain. Complex eyes can differentiate between shapes and colours and simple eyes can only detect when an area is light or dark. The eyes are bedded in the orbit, six long thin muscle run from the orbit to the outer surface of the eye. When they contract together it enables the eye to move in unison and the image on the retinae correspond.




The shape of the eye is round with a transparent window, the cornea infront and the optic nerve behind, and then behind the cornea is the lens, with a ring like shape, that is known as the iris that is infront. The eyes are protected by connective tissue and is cushioned by fat, behind the lens is filled with a jelly substance the vitreous body, that maintains the shape of the eye. The vitreous body is the transparent, colourless, gelatinous mass that fills the space between the lens of the eye and the retina lining the back of the eye.

The eye pupil is the central hole in the iris, it varies in size and controls the amount of light that is passed through to the retina. When the environment is bright the eye pupil shrinks and when its dark it becomes enlarged.
The retina contains two major types of light-sensitive photoreceptor cells. The eye is lined by the retina which consists large numbers of nerve cells, rods and cones which is layered with light absorbing pigment, known as the (choroid).
The rods are sensitive to faint light, are numerous and spread all over the retina. Rods cannot distinguish colours, but are responsible for low-light (scotopic) monochrome (black-and-white) vision, the rods has a sensitive pigment called (visual purple) that is quickly bleached by bright light. Rods are distributed throughout the retina but there are none at the fovea and none at the blind spot. Rod density is greater in the peripheral retina than in the central retina.
The cones are very sensitive to bright coloured lights, it is at the focal point of the eye the (macula). In humans, there are three types of cones, long-wavelength, medium-wavelength, and short-wavelength light (often referred to as red, green, and blue. When cones and rods are stimulated by light, they connect through adjoining cells within the retina to send an electrical signal to the optic nerve fibres.
The eye muscles has sensitive receptors that signals the nervous system for accurate eye movement. The muscles are controlled by motor nerve fibres cell groups (nucleii) connected in the brain stem that forms the third, fourth and six pairs of cranial nerves. The ocular motor nucleii are adjoined by nerve cells that signal patterns that are discharged. The pattern for these signals, reflects the way how our vision of awareness, shape, size and colour arises.



By: V.Goldson



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