A human eye has a ball-shaped form, so the name comes from it – an eyeball. It consists from three layers: external, vascular and retinal, as well as from internal content.
The anterior part of the external layer is cornea – similar to a transparent window into the external world. Light beams go through it to the internal part of the eye. It has a curved form and not only lets the beams through but also bends them. The remaining part of the external layer – sclera - is not transparent and is similar to a boiled egg white.
The second layer – vascular – consists from multiple small vessels. Blood supplies the eye with oxygen and nutrients via the vessels. There are also several parts in this layer: anterior – iris, medium - cilliar body and posterior – choroid. Colour of our eyes is determined by the pigment content in iris that is visible through cornea. There is a round opening – a pupil - in the centre of iris. Its size is changing depending on the light: it enlarges in darkness and decreases in bright light.
The space between cornea and iris is called the anterior chamber. The cilliar body is producing intraocular liquid that circulates inside the eye, washing and feeding the cornea, lens, vitreous body. This liquid is circulating through a special drainage system to the angle of the camera anterior. Acommodation muscle, regulating the form of the lens by ligaments, is placed in the depth of the cilliar body.
Choroid – the posterior part of the vascular layer – is contacting directly with retina, ensuring it with necessary nutrients.
Choroid – the posterior part of the vascular layer – is contacting directly with retina, ensuring it with necessary nutrients.
The beams of light are focused on retina, internal layer of the eye. They are processed into neural impulses and transferred to the brain along the optic nerve.
Anterior and posterior cameras, filled with intraocular liquid, as well as lens and vitreous body are placed inside the layers (between iris and lens). The lens has a convex form. It lets through and bends light beams as cornea does, it also focuses the image on the retina. Vitreous has a gel consistency and separates the lens from the fundus oculi.
The coinciding action of all parts of the eye enables us to see in a close and far distance, at day and darkness, to see difference of colours, to orientate ourselves in the environment.
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