Eyes
DESCRIPTION
The eye is the body's link to the visible environment. It is a complex organ designed to collect and focus light which is then converted by the retina into an electrical signal and sent to the occipital lobe of the brain for processing and interpretation.
Optic nerve
DESCRIPTION
The optic nerve is the large nerve bundle that exits from the back of the eye. It is made up of over 2 million individual nerves, measures about 4mm in diameter and carries the electrical signals from the eye to the brain. Head trauma can damage the optic nerve in several ways. A blow to the head can disrupt the blood flow to the optic nerve or it can cause a bone to break and press on the optic nerve. This type injury is usually called a traumatic optic neuropathy and can result in partial to complete loss of vision in the affected eye.
Optic chiasm
DESCRIPTION
The optic chiasm is the point where the two optic nerves intersect. In the chiasm part of the nerve fibres from each optic nerve cross to the opposite side of the brain and combine with the remaining fibres from the other optic nerve. This results in most of the right visual field from both eyes going to the left side of the brain and most of the left visual field from both eyes going to the right side of the brain. At this point injuries change from affecting the visual field of one eye, to affecting both eyes.
Optic tract
DESCRIPTION
The combined nerve fibres from the two optic nerves form the optic tract on each side of the brain. The optic tracts extend from the optic chiasm to a point midway to the occipital lobe of the brain called the lateral geniculate nucleus.
Optic radiation
DESCRIPTION
The part of the visual pathway that extends from the lateral geniculate nuclei to the occipital lobes are called the optic radiations. The optic radiations carry the electrical signals that originated in the eye the final distance to the occipital lobes.
Occipital lobe
DESCRIPTION
The occipital lobes are located in the back of the brain and are the smallest of the four lobes. They are the visual center, and are the primary portion of the brain responsible for receiving input from the eyes.
FUNCTION
The occipital lobes receive and process all input from the eyes. Area A is the primary visual cortex and the recipient of visual input from the eyes. Area A performs the initial processing of the information, for example combining input from the two eyes, and beginning to analyse depth. This information is then passed on to Areas B and C. Areas B and C are the associative visual cortex, where motion, color, and other parameters are interpreted to provide meaning.
RESULT OF INJURY
Damage to the right occipital lobe can result in loss of the left visual field of both eyes, and damage to the left occipital lobe results in loss of the right visual field of both eyes. Damage to both the left and right occipital lobes can result in blindness, even though the eyes themselves may be functioning normally. This condition is called cortical blindness. If the front part of the occipital lobe is damaged, people have difficulty recognising familiar objects and faces and accurately interpreting what they see.