Optic Neuropathy
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Optic neuropathy is damage to the
optic nerve In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual system, visual information from the retina to the brain. In humans, the optic nerve i ...
from any cause. The optic nerve is a bundle of millions of fibers in the retina that sends visual signals to the brain. Damage and death of these nerve cells, or neurons, leads to characteristic features of optic neuropathy. The main symptom is loss of vision, with colors appearing subtly washed out in the affected eye. A pale disc is characteristic of long-standing optic neuropathy. In many cases, only one eye is affected and patients may not be aware of the loss of color vision until the doctor asks them to cover the healthy eye. Optic neuropathy is often called optic atrophy, to describe the loss of some or most of the fibers of the optic nerve.


Ischemic optic neuropathy

In ischemic optic neuropathies, there is insufficient blood flow (ischemia) to the optic nerve. The anterior optic nerve is supplied by the short posterior ciliary artery and choroidal circulation, while the retrobulbar optic nerve is supplied intraorbitally by a pial plexus, which arises from the ophthalmic artery, internal carotid artery, anterior cerebral artery, and anterior communicating arteries. Ischemic optic neuropathies are classified based on the location of the damage and the cause of reduced blood flow, if known. * Anterior ischemic optic neuropathy (AION) includes diseases that affect the optic nerve head and cause swelling of the optic disc. These diseases often cause sudden rapid visual loss in one eye. Inflammatory diseases of the blood vessels, like
giant-cell arteritis Giant cell arteritis (GCA), also called temporal arteritis, is an inflammatory autoimmune disease of large blood vessels. Symptoms may include headache, pain over the temples, flu-like symptoms, double vision, and difficulty opening the mouth. ...
, polyarteritis nodosa, Churg–Strauss syndrome,
granulomatosis with polyangiitis Granulomatosis with polyangiitis (GPA), previously known as Wegener's granulomatosis (WG), is a rare long-term systemic disorder that involves the formation of granulomas and inflammation of blood vessels (vasculitis). It is a form of vasculitis ...
, and rheumatoid arthritis can cause arteritic AIONs (AAION). The vast majority of AIONs are nonarteritic AIONs (NAION). The most common acute optic neuropathy in patients over 50 years of age, NAION has an annual incidence of 2.3-10.2/100,000. NAION presents as a painless loss of vision, often when awakening, that occurs over hours to days. Most patients lose the lower half of their visual field (an inferior altitudinal loss), though superior altitudinal loss is also common. The pathophysiology of NAION is unknown, but it is related to poor circulation in the optic nerve head. NAION is often associated with diabetes mellitus, elevated intraocular pressure (acute glaucoma, eye surgery), high cholesterol, hypercoagulable states, a drop in blood pressure (bleeding, cardiac arrest, peri-operative esp. cardiac and spine procedures), and sleep apnea. Rarely, amiodarone, interferon-alpha, and erectile dysfunction drugs have been associated with this disease. * Posterior ischemic optic neuropathy is a syndrome of sudden visual loss with optic neuropathy without initial disc swelling with subsequent development of optic atrophy. This can occur in patients who are predisposed to AAION and NAION as described above as well as those who had cardiac and spine surgery or serious episodes of hypotension. *Radiation optic neuropathy (RON) is also thought to be due to ischemia of the optic nerve that occurs 3 months to 8 or more years after radiation therapy to the brain and orbit. It occurs most often around 1.5 years after treatment and results in irreversible and severe vision loss, which may also be associated with damage to the retina (radiation retinopathy). This is thought to be due to damage to dividing glial and vascular endothelial cells. RON can present with transient visual loss followed by acute painless visual loss in one or both eyes several weeks later. The risk of RON is significantly increased with radiation doses over 50 Gy.


Optic neuritis

Optic neuritis Optic neuritis describes any condition that causes inflammation of the optic nerve; it may be associated with demyelinating diseases, or infectious or inflammatory processes. It is also known as optic papillitis (when the head of the optic nerv ...
is inflammation of the optic nerve, which is associated with swelling and destruction of the myelin sheath covering the optic nerve. Young adults, usually females, are most commonly affected. Symptoms of optic neuritis in the affected eye include pain on eye movement, sudden loss of vision, and decrease in color vision (especially reds). Optic neuritis, when combined with the presence of multiple demyelinating white matter brain lesions on MRI, is suspicious for
multiple sclerosis Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This d ...
. Several causes and clinical courses are possible for the optic neuritis. It can be classified in: * Single isolated optic neuritis (SION) * relapsing isolated optic neuritis (RION) *
chronic relapsing inflammatory optic neuropathy Chronic relapsing inflammatory optic neuropathy (CRION) is a form of recurrent optic neuritis that is steroid responsive and dependent. Patients typically present with pain associated with visual loss. CRION is a clinical diagnosis of exclusion, ...
(CRION) * the neuromyelitis optica (NMO) spectrum disorder * multiple sclerosis associated optic neuritis (MSON) * unclassified optic neuritis (UCON) forms. Medical examination of the optic nerve with an ophthalmoscope may reveal a swollen optic nerve, but the nerve may also appear normal. Presence of an afferent pupillary defect, decreased color vision, and visual field loss (often central) are suggestive of optic neuritis. Recovery of visual function is expected within 10 weeks. However, attacks may lead to permanent axonal loss and thinning of the retinal nerve fiber layer.


Compressive optic neuropathy

Tumors, infections, and inflammatory processes can cause lesions within the orbit and, less commonly, the optic canal. These lesions may compress the optic nerve, resulting optic disc swelling and progressive visual loss. Implicated orbital disorders include optic gliomas, meningiomas, hemangiomas, lymphangiomas, dermoid cysts, carcinoma, lymphoma, multiple myeloma, inflammatory orbital pseudotumor, and thyroid ophthalmopathy. Patients often have bulging out of the eye (proptosis) with mild color deficits and almost normal vision with disc swelling.


Infiltrative optic neuropathy

The optic nerve can be infiltrated by a variety of processes, including tumors, inflammation, and infections. Tumors that can infiltrate the optic nerve can be primary (optic gliomas, capillary hemangiomas, and cavernous hemangiomas) or secondary (metastatic carcinoma, nasopharyngeal carcinoma, lymphoma, and leukemia). The most common inflammatory disorder that infiltrates the optic nerve is
sarcoidosis Sarcoidosis (also known as ''Besnier-Boeck-Schaumann disease'') is a disease involving abnormal collections of inflammatory cells that form lumps known as granulomata. The disease usually begins in the lungs, skin, or lymph nodes. Less commonly af ...
. Opportunistic fungi, viruses, and bacteria may also infiltrate the optic nerve. The optic nerve may be elevated if the infiltration occurs in the proximal portion of the nerve. The appearance of the nerve on examination depends on the portion of the nerve that is affected.


Traumatic optic neuropathy

The optic nerve can be damaged when exposed to direct or indirect injury. Direct optic nerve injuries are caused by trauma to the head or orbit that crosses normal tissue planes and disrupts the anatomy and function of the optic nerve; e.g., a bullet or forceps that physically injures the optic nerve. Indirect injuries, like blunt trauma to the forehead during a motor vehicle accident, transmit force to the optic nerve without transgressing tissue planes. This type of force causes the optic nerve to absorb excess energy at the time of impact. The most common site of injury of the optic nerve is the intracanalicular portion of the nerve. Deceleration injuries from motor vehicle or bicycle accidents account for 17 to 63 percent of cases. Falls are also a common cause, and optic neuropathy most commonly occurs when there is a loss of consciousness associated with multi-system trauma and serious brain injury. In less than three percent of patients, an orbital hemorrhage after an injection behind the eye (retrobulbar block) can cause injury to the optic nerve, but this is readily manageable if it does not involve direct optic nerve injury and is caught early. The role of high-dose steroids and orbital decompression in treating these patients is controversial and, if administered, must be done very soon after injury with minimal effects. In patients with an orbital fracture, vomiting or nose blowing can force air into the orbit and possibly compromise the integrity of the optic nerve.


Mitochondrial optic neuropathies

Mitochondria A mitochondrion (; ) is an organelle found in the Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...
play a central role in maintaining the life cycle of retinal ganglion cells because of their high energy dependence. Mitochondria are made within the central somata of the retinal ganglion cell, transported down axons, and distributed where they are needed. Genetic mutations in mitochondrial DNA, vitamin depletion, alcohol and tobacco abuse, and use of certain drugs can cause derangements in efficient transport of mitochondria, which can cause a primary or secondary optic neuropathy.


Nutritional optic neuropathies

A nutritional optic neuropathy may be present in a patient with obvious evidence of under-nutrition (weight loss and wasting). Months of depletion are usually necessary to deplete body stores of most nutrients. Undernourished patients often have many vitamin and nutrient deficiencies and have low serum protein levels. However, the optic neuropathy associated with
pernicious anemia Pernicious anemia is a type of vitamin B12 deficiency anemia, a disease in which not enough red blood cells are produced due to the malabsorption of vitamin B12. Malabsorption in pernicious anemia results from the lack or loss of intrinsic fa ...
and vitamin B12 deficiency can even be seen in well-nourished individuals. Gastric bypass surgery may also cause a vitamin B12 deficiency from poor absorption. Patients who have nutritional optic neuropathy may notice that colors are not as vivid or bright as before and that the color red is washed out. This normally occurs in both eyes at the same time and is not associated with any eye pain. They might initially notice a blur or fog, followed by a drop in vision. While vision loss may be rapid, progression to blindness is unusual. These patients tend to have blind spots in the center of their vision with preserved peripheral vision. In most cases, the pupils continue to respond normally to light.


Toxic optic neuropathies

The most recognized cause of toxic optic neuropathy is methanol poisoning. This can be a life-threatening event that normally accidentally occurs when the person mistook or substituted,
methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a ...
for
ethyl alcohol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a hyd ...
. The patient initially has nausea and vomiting, followed by respiratory distress, headache, and visual loss 18–48 hours after consumption. Without treatment, patients can go blind, and their pupils will dilate and stop reacting to light. *
Ethylene glycol Ethylene glycol (IUPAC name: ethane-1,2-diol) is an organic compound (a vicinal diol) with the formula . It is mainly used for two purposes, as a raw material in the manufacture of polyester fibers and for antifreeze formulations. It is an odo ...
, a component of automobile antifreeze, is a poison that is toxic to the whole body including the optic nerve. Consumption can be fatal, or recovery can occur with permanent neurologic and ophthalmologic deficits. While the visual loss is not very common, increased intracranial pressure can cause bilateral optic disc swelling from cerebral edema. A clue to the cause of intoxication is the presence of oxalate crystals in the urine. Like methanol intoxication, treatment is ethanol consumption. *
Ethambutol Ethambutol (EMB, E) is a medication primarily used to treat tuberculosis. It is usually given in combination with other tuberculosis medications, such as isoniazid, rifampicin and pyrazinamide. It may also be used to treat ''Mycobacterium avi ...
, a drug commonly used to treat tuberculosis, is notorious for causing toxic optic neuropathy. Patients with vision loss from ethambutol toxicity lose vision in both eyes equally. This initially presents with problems with colors (dyschromatopsia) and can leave central visual deficits. If vision loss occurs while using ethambutol, it would be best to discontinue this medication under a doctor's supervision. Vision can improve slowly after discontinuing ethambutol but rarely returns to baseline. *
Amiodarone Amiodarone is an antiarrhythmic medication used to treat and prevent a number of types of cardiac dysrhythmias. This includes ventricular tachycardia (VT), ventricular fibrillation (VF), and wide complex tachycardia, as well as atrial fibrilla ...
is an antiarrhythmic medication commonly used for abnormal heart rhythms (atrial or ventricular tachyarrhythmias). Most patients on this medication get corneal epithelial deposits, but this medication has also been controversially associated with NAION. Patients on amiodarone with new visual symptoms should be evaluated by an ophthalmologist. *
Tobacco Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ...
exposure, most commonly through pipe and cigar smoking, can cause optic neuropathy. Middle-aged or elderly men are often affected and present with painless, slowly progressive, color distortion and visual loss in both eyes. The mechanism is unclear, but this has been reported to be more common in individuals who are already suffering from malnutrition.


Hereditary optic neuropathies

The inherited optic neuropathies typically manifest asa symmetric bilateral central visual loss. Optic nerve damage in most inherited optic neuropathies is permanent and progressive. * Leber's hereditary optic neuropathy (LHON) is the most frequently occurring mitochondrial disease, and this inherited form of acute or subacute vision loss predominantly affects young males. LHON usually presents with rapid vision loss in one eye followed by involvement of the second eye (usually within months). Visual acuity often remains stable and poor (around or below 20/200) with a residual central visual field defect. Patients with the 14484/ND6 mutation are most likely to have visual recovery. *
Dominant optic atrophy Dominant optic atrophy, or dominant optic atrophy, Kjer's type, is an autosomally inherited disease that affects the optic nerves, causing reduced visual acuity and blindness beginning in childhood. This condition is due to mitochondrial dysfuncti ...
is an autosomal dominant disease caused by a defect in the nuclear gene OPA1. A slowly progressive optic neuropathy, dominant optic atrophy, usually presents in the first decade of life and is bilaterally symmetrical. Examination of these patients shows loss of visual acuity, temporal pallor of the optic discs, centrocecal scotomas with peripheral sparing, and subtle impairments in color vision. *
Behr's syndrome Behr syndrome is characterized by the association of early-onset optic atrophy with spinocerebellar degeneration resulting in ataxia, pyramidal signs, peripheral neuropathy and developmental delay. Although it is an autosomal recessive disorder, ...
is a rare autosomal recessive disorder characterized by early-onset optic atrophy, ataxia, and spasticity. *
Berk–Tabatznik syndrome Berk–Tabatznik syndrome is a medical condition with an unknown cause that shows symptoms of short stature, congenital optic atrophy and brachytelephalangy. This condition is extremely rare with only two cases being found. See also * Heart-han ...
is a condition that shows symptoms of short stature, congenital optic atrophy and brachytelephalangy. This condition is extremely rare.


Optic nerve

The
optic nerve In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual system, visual information from the retina to the brain. In humans, the optic nerve i ...
contains
axons An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, th ...
of nerve cells that emerge from the
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...
, leave the eye at the
optic disc The optic disc or optic nerve head is the point of exit for ganglion cell axons leaving the eye. Because there are no rods or cones overlying the optic disc, it corresponds to a small blind spot in each eye. The ganglion cell axons form the ...
, and go to the
visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and ...
where input from the eye is processed into vision. There are 1.2 million optic nerve fibers that derive from the
retinal ganglion cells A retinal ganglion cell (RGC) is a type of neuron located near the inner surface (the ganglion cell layer) of the retina of the eye. It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and retina ...
of the inner retina.


Treatments

While optic neuropathy cannot be outright cured, there are surgical options to alleviate pain and symptoms associated with such diseases. The Endoscopic Endonasal Approach method (EEA) is a preferred method of relieving pressure associated with tumors formed in the brain that press upon the optic nerve. It is a minimally invasive surgery. However, due to the genetic and developmental nature of most causes of optic neuropathy, no other surgeries have been proven to cure these diseases.


See also

*
Optic neuritis Optic neuritis describes any condition that causes inflammation of the optic nerve; it may be associated with demyelinating diseases, or infectious or inflammatory processes. It is also known as optic papillitis (when the head of the optic nerv ...
*
Ophthalmoplegia Ophthalmoparesis refers to weakness (-paresis) or paralysis (-plegia) of one or more extraocular muscles which are responsible for eye movements. It is a physical finding in certain neurologic, ophthalmologic, and endocrine disease. Internal o ...
*
Glaucoma Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle (wide angle, chronic simple) glaucoma, in which the drainage angle for fluid within the eye rem ...


References


External links


NCBI Genetic Testing Registry
{{Eye pathology Eye diseases