The human eye is a remarkable thing. Although it is small in size, the eye arguably provides us with the most important of the five senses - vision.
Vision occurs when light enters the eye through the pupil; with help from other important structures in the eye the iris and cornea the appropriate amount of light is directed towards the lens.
Just like a lens in a camera sends a message to produce a film; the lens in the eye refracts incoming light onto the retina, where messages are encoded. The retina, which is made up by millions of specialised cells known as rods and cones, transforms the image into electrical energy and this is sent to the optic disk on the retina where it will be transferred via electrical impulses along the optic nerve to be processed by the brain.
Eye Anatomy Terms
The choroid is the middle layer of the eye between the retina and the sclera. It also contains a pigment that absorbs excess light so preventing blurring of vision.
The ciliary body is the part of the eye that connects the choroid to the iris.
Are one of two types of light sensitive cells in the retina of the eye. The human retina contains 6-7 million cones; they function best in bright light and are essential for acute vision (receiving a sharp accurate image). The area of the retina called the fovea contains the greatest concentration of cones. It is thought that there are three types of cones, each sensitive to the wavelength of a different primary colour - red green or blue. Other colours are seen as combinations of these primary colours.
The transparent circular part of the front of the eyeball. It refracts the light entering the eye onto the lens, which then focuses it onto the retina. The cornea contains no blood vessels and is extremely sensitive to pain.
The fovea forms a small indentation at the centre of the macula and is described as the area with the greatest concentration of cone cells, the messages encoded at the centre of the fovea will be interpreted by the brain in the form of a visual image.
The iris regulates the amount of light that enters the eye. It forms a coloured muscular diaphragm across the front of the lens. Light enters through a central opening called the pupil.
The lens is a transparent crystalline structure situated behind the pupil of the eye and it is enclosed in a thin transparent capsule. It helps to refract incoming light and focus it onto the retina. A cataract is when the lens becomes cloudy, and can be extracted through a practice known as Phacoemulsification and replaced with a plastic intraocular lens.
Is the yellow spot on the retina at the back of the eye, which surrounds the fovea, the area with the greatest concentration of cone cells, and is therefore the area of greatest acuity of vision. When the eye is directed at an object, the part of the image that is focused on the fovea is the image most accurately registered by the brain.
Is the visible portion of the optic nerve also found on the retina of the eye. The optic disk identifies the start of the optic nerve where messages from cone and rod cells leave the eye via nerve fibres to the optic centre of the brain. This area is also known as the 'blind spot'.
Is a continuation of the retina, leaving the eye at the optic disk, and transfers all the visual information to the brain, via millions of nerve fibres branching from the rods and cones.
The circular opening in the centre of the iris through which light passes into the lens of the eye. The iris controls dilation and constriction of the pupil.
Is a light sensitive layer that lines the interior of the eye. It is composed of light sensitive cells known as rods and cones. The human eye contains about 125 million rods, which are necessary for seeing in dim light. Cones on the other hand function best in bright light - there are between 6 and 7 million in the eye - they are essential for receiving a sharp accurate image; cones can also distinguish colours. The retina works much in the same way as film in a camera.
The white part of the eye, a tough covering with which the cornea forms the external protective coat of the eye.
Are one of the two types of light-sensitive cells in the retina of the eye. There are about 125 million rods, which are necessary for seeing in dim light. They contain a pigment 'rhodopsin' (or visual purple) which is broken down in the light and regenerated in the dark. Breakdown of visual purple gives rise to nerve impulses when all the pigment is bleached (i.e. in bright light) and the rods no longer function; this is when the cones are activated.