The optic nerve, which carries about one million nerve fibres, is located at the back of the eye and passes through the apex of the orbit into the cranial cavity. It is surrounded by membranes that encircle the brain. This connection with the intracranial cavity is critical because some intracranial diseases cause increased pressure within the skull. Increased pressure travels along the covering of the optic nerve leading to swelling of the optic nerve head, a condition that is visible inside the eye. This swelling of the nerve head of each eye (often known as papilledema) is one of the common symptoms of increased intracranial pressure. If the swelling continues, fibres of the optic nerve can be damaged, with subsequent loss of vision.
Inflammatory changes in the optic nerve may also lead to its swelling, a condition known as optic neuritis. Some of the common signs include loss of vision in or near the central part of the visual field, pain behind the eye, and pain when moving the eye. The condition is most common in young adults and may be an indication of multiple sclerosis. Multiple sclerosis is a health condition in which the sheaths of the nerves change and interfere with the transmission of nervous impulses. This disease may affect any part of the nervous system, but the optic nerve is a common site, and vision loss or eye pain is often the first symptoms to be noticed by the patient. Normally, optic nerve functionality recovers after an episode of optic neuritis however, visual disturbance often remains.
Optic nerve damage or atrophy may result from glaucoma or any serious disease of the retina in which a large amount of neural tissue has been destroyed. It may also cause damage to the optic nerve within the skull, where the optic nerves interweave. For example, tumours of the pituitary gland often compress the optic nerve fibres and cause some degree of atrophy with loss of vision in that part of the visual field. Usually it is the fibres on the inner side of the optic nerve and those that cross at the chiasm that are involved.
Certain chemicals, drugs, and nutritional deficiencies can also cause optic nerve damage or atrophy. If the underlying cause is corrected in time with the help of a qualified ophthalmologist, some vision improvement may occur.
is the name given to a group of diseases that cause a particular form of optic nerve disease
that causes visual field loss. Increased pressure within the eye is one of several important risk factors for development of glaucoma, but no one particular pressure is indicative of the disease. Causes of glaucoma include chronic inflammatory disease
of the eye, tumours within the eye
, and congenital afflictions of the eye. Congenital glaucoma
usually is found in the neonatal period and is followed by tearing, aversion to light, eyelid spasms
, and clouding and enlargement of the cornea. Treatment is aimed at medically or surgically reducing intraocular pressure, but long-term visual prognosis is often poor.