Perioperative PION patients have a higher prevalence of cardiovascular risk factors than in the general population. Documented cardiovascular risks in people affected by perioperative PION include high blood pressure, diabetes mellitus, high levels of cholesterol in the blood, tobacco use, abnormal heart rhythms, stroke, and obesity. Men are also noted to be at higher risk, which is in accordance with the trend, as men are at higher risk of cardiovascular disease. These cardiovascular risks all interfere with adequate blood flow, and also may suggest a contributory role of defective vascular autoregulation.

Toxic optic neuropathy refers to the ingestion of a toxin or an adverse drug reaction that results in vision loss from optic nerve damage. Patients may report either a sudden loss of vision in both eyes, in the setting of an acute intoxication, or an insidious asymmetric loss of vision from an adverse drug reaction. The most important aspect of treatment is recognition and drug withdrawal.

Among the many causes of TON, the top 10 toxins include:

- Medications

- Ethambutol, rifampin, isoniazid, streptomycin (tuberculosis treatment)

- Linezolid (taken for bacterial infections, including pneumonia)

- Chloramphenicol (taken for serious infections not helped by other antibiotics)

- Isoretinoin (taken for severe acne that fails to respond to other treatments)

- Ciclosporin (widely used immunosuppressant)

- Acute Toxins

- Methanol (component of some moonshine, and some cleaning products)

- Ethylene glycol (present in anti-freeze and hydraulic brake fluid)

Metabolic disorders may also cause this version of disease. Systemic problems such as diabetes mellitus, kidney failure, and thyroid disease can cause optic neuropathy, which is likely through buildup of toxic substances within the body. In most cases, the cause of the toxic neuropathy impairs the tissue’s vascular supply or metabolism. It remains unknown as to why certain agents are toxic to the optic nerve while others are not and why particularly the papillomacular bundle gets affected.

As illustrated by the risk factors above, perioperative hypoxia is a multifactorial problem. Amidst these risk factors it may be difficult to pinpoint the optic nerve’s threshold for cell death, and the exact contribution of each factor.

Low blood pressure and anemia are cited as perioperative complications in nearly all reports of PION, which suggests a causal relationship. However, while low blood pressure and anemia are relatively common in the perioperative setting, PION is exceedingly rare. Spine and cardiac bypass surgeries have the highest estimated incidences of PION, 0.028% and 0.018% respectively, and this is still extremely low. This evidence suggests that optic nerve injury in PION patients is caused by more than just anemia and low blood pressure.

Evidence suggests that the multifactorial origin of perioperative PION involves the risks discussed above and perhaps other unknown factors. Current review articles of PION propose that vascular autoregulatory dysfunction and anatomic variation are under-investigated subjects that may contribute to patient-specific susceptibility.

Although many perinatal and prenatal risk factors for ONH have been suggested, the predominant, enduring, most frequent risk factors are young maternal age and primiparity (the affected child being the first child born to the mother). Increased frequency of delivery by caesarean section and fetal/neonatal complications, preterm labor, gestational vaginal bleeding, low maternal weight gain, and weight loss during pregnancy are also associated with ONH.

TAA is an old term for a constellation of elements that can lead to a mitochondrial optic neuropathy. The classic patient is a man with a history of heavy alcohol and tobacco consumption. Respectively, this combines nutritional mitochondrial impairment, from vitamin deficiencies (folate and B-12) classically seen in alcoholics, with tobacco-derived products, such as cyanide and ROS. It has been suggested that the additive effect of the cyanide toxicity, ROS, and deficiencies of thiamine, riboflavin, pyridoxine, and b12 result in TAA.

Mutations of genes involved in transcription regulation, chromatin remodelling, α-dystroglycan glycosylation, cytoskeleton and scaffolding protein, RNA splicing, and the MAP kinase signalling pathway are currently known to cause ONH. Many transcription factors for eye development are also involved in the morphogenesis of forebrain, which may explain why ONH is commonly a part of a syndrome involving brain malformations.

ONH impacts all ethnic groups, although in the United States, occurrence is lower in persons of Asian descent. To date, there have been few reports of ONH occurrence in Asian countries, although it is uncertain why this is so.

It is estimated that the incidence of AION is about 8,000/year in the U.S.

The predominant cause of nutritional optic neuropathy is thought to be deficiency of B-complex vitamins, particularly thiamine (vitamin B), cyanocobalamin (vitamin B) and recently copper Deficiency of pyridoxine (vitamin B), niacin (vitamin B), riboflavin (vitamin B), and/or folic acid also seems to play a role. Those individuals who abuse alcohol and tobacco are at greater risk because they tend to be malnourished. Those with pernicious anemia are also at risk due to an impaired ability to absorb vitamin B from the intestinal tract.

There are several causes of toxic optic neuropathy. Among these are: ingestion of methanol (wood alcohol), ethylene glycol (automotive antifreeze), disulfiram (used to treat chronic alcoholism), halogenated hydroquinolones (amebicidal medications), ethambutol and isoniazid (tuberculosis treatment), and antibiotics such as linezolid and chloramphenicol. Tobacco is also a major cause of toxic optic neuropathy.

The mechanism of injury for NAION used to be quite controversial. However, experts in the field have come to a consensus that most cases involve two main risk factors. The first is a predisposition in the form of a type of optic disc shape. The optic disc is where the axons from the retinal ganglion cells collect into the optic nerve. The optic nerve is the bundle of axons that carry the visual signals from the eye to the brain. This optic nerve must penetrate through the wall of the eye, and the hole to accommodate this is usually 20-30% larger than the nerve diameter. In some patients the optic nerve is nearly as large as the opening in the back of the eye, and the optic disc appears "crowded" when seen by ophthalmoscopy. A crowded disc is also referred to as a "disc at risk". While a risk factor, the vast majority of individuals with crowded discs do not experience NAION.

The second major risk factor involves more general cardiovascular risk factors. The most common are diabetes, hypertension and high cholesterol levels. While these factors predispose a patient to develop NAION, the most common precipitating factor is marked fall of blood pressure during sleep (nocturnal arterial hypotension)- that is why at least 75% of the patients first discover visual loss first on waking from sleep. These vascular risk factors lead to ischemia (poor blood supply) to a portion of the optic disc. The disc then swells, and in a crowded optic disc, this leads to compression and more ischemia.

Since both eyes tend to have a similar shape, the optometrist or ophthalmologist will look at the good eye to assess the anatomical predisposition. The unaffected eye has a 14.7% risk of NAION within five years.

A number of uncontrolled single case or small number of patient reports have associated NAION with use of oral erectile dysfunction drugs.

About 1–2% of all meningiomas are optic nerve sheath meningiomas. Meningiomas have an incidence of ~4.18/100,000 persons each year. Thus, ~10,000 meningiomas are diagnosed in the US each year; corresponding to ~100 cases of ONSM each year in the US. The actual number of meningiomas is likely much higher as it is very common in elderly women. ONSM comprises about 2% of orbital tumors, and about 10% of optic nerve lesions.

Neurofibromatosis type II (NF-2) affects around 9% of ONSM patients, where the incidence in the general population is around 0.03–0.05%. Thus NF-2 is felt to be a risk factor for the development of ONSM.

The incidence of dominant optic atrophy has been estimated to be 1:50000 with prevalence as high as 1:10000 in the Danish population (Votruba, 1998). Dominant optic atrophy is inherited in an autosomal dominant manner. That is, a heterozygous patient with the disease has a 50% chance of passing on the disease to offspring, assuming his/her partner does not have the disease. Males and females are affected at the same rate. Although Kjer's has a high penetrance (98%), severity and progression of DOA are extremely variable even within the same family.

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, polyarteritis nodosa, Churg-Strauss syndrome, granulomatosis with polyangiitis, 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.

- There is also some evidence that interferon treatment (pegylated interferon with ribavirin) for hepatitis C virus can cause optic neuropathy.

Optic gliomas often have a shifting clinical course, with sporadic periods of vision loss separated by long periods of visual stability. Optic gliomas rarely spontaneously regress.

Optic neuritis typically affects young adults ranging from 18–45 years of age, with a mean age of 30–35 years. There is a strong female predominance. The annual incidence is approximately 5/100,000, with a prevalence estimated to be 115/100,000.

The most common finding is oculomotor nerve dysfunction leading to ophthalmoplegia. This is often accompanied by ophthalmic nerve dysfunction, leading to hypoesthesia of the upper face. The optic nerve may eventually be involved, with resulting visual impairment.

The most recognized cause of a toxic optic neuropathy is methanol intoxication. This can be a life-threatening event that normally accidentally occurs when the victim mistook, or substituted, methanol for ethyl alcohol. Blindness can occur with drinking as little as an ounce of methanol, but this can be counteracted by concurrent drinking of ethyl alcohol. 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, 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 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, 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 is an antiarrhythmic medication commonly used for abnormal heart rhythms (atrial or ventricular tachyarrythmias). 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 exposure, most commonly through pipe and cigar smoking, can cause an 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.

Foroozen divides the causes of chiasmal syndromes into intrinsic and extrinsic causes. Intrinsic implies thickening of the chiasm itself and extrinsic implies compression by another structure. Other less common causes of chiasmal syndrome are metabolic, toxic, traumatic or infectious in nature.

Intrinsic etiologies include gliomas and multiple sclerosis. Gliomas of the optic chiasm are usually derived from astrocytes. These tumors are slow growing and more often found children. However, they have a worse prognosis, especially if they have extended into the hypothalamus. They are frequently associated with neurofibromatosis type 1 (NF-1). Their treatment involves the resection of the optic nerve. The supposed artifactual nature of Wilbrand's knee has implications for the degree of resection that can be obtained, namely by cutting the optic nerve immediately at the junction with the chiasm without fear of potentially resulting visual field deficits.

The vast majority of chiasmal syndromes are compressive. Ruben et al. describe several compressive etiologies, which are important to understand if they are to be successfully managed. The usual suspects are pituitary adenomas, craniopharyngiomas, and meningiomas.

Pituitary tumors are the most common cause of chiasmal syndromes. Visual field defects may be one of the first signs of non-functional pituitary tumor. These are much less frequent than functional adenomas. Systemic hormonal aberrations such as Cushing’s syndrome, galactorrhea and acromegaly usually predate the compressive signs. Pituitary tumors often encroach upon the middle chiasm from below. Pituitary apoplexy is one of the few acute chiasmal syndromes. It can lead to sudden visual loss as the hemorrhagic adenoma rapidly enlarges.

The embryonic remnants of Rathke’s pouch may undergo neoplastic change called a craniopharyngioma. These tumors may develop at any time but two age groups are most at risk. One peak occurs during the first twenty years of life and the other occurs between fifty and seventy years of age. Craniopharyngiomas generally approach the optic chiasm from behind and above. Extension of craniopharyngiomas into the third ventricle may cause hydrocephalus.

Meningiomas can develop from the arachnoid layer. Tuberculum sellae and sphenoid planum meningiomas usually compress the optic chiasm from below. If the meningioma arises from the diaphragma sellae the posterior chiasm is damaged. Medial sphenoid ridge types can push on the chiasm from the side. Olfactory groove subfrontal types can reach the chiasm from above. Meningiomas are also associated with neurofibromatosis type 1. Women are more prone to develop meningiomas.

The treatment, and therefore prognosis, varies depending upon the underlying tumour.

Optic disc drusen are found clinically in about 1% of the population but this increases to 3.4% in individuals with a family history of ODD. About two thirds to three quarters of clinical cases are bilateral. A necropsy study of 737 cases showed a 2.4% incidence with 2 out of 15 (13%) bilateral, perhaps indicating the insidious nature of many cases. An autosomal dominant inheritance pattern with incomplete penetrance and associated inherited dysplasia of the optic disc and its blood supply is suspected. Males and females are affected at equal rates. Caucasians are the most susceptible ethnic group. Certain conditions have been associated with disc drusen such as retinitis pigmentosa, angioid streaks, Usher syndrome, Noonan syndrome and Alagille syndrome. Optic disc drusen are not related to Bruch membrane drusen of the retina which have been associated with age-related macular degeneration.

Jacod Syndrome is commonly associated with a tumor of the middle cranial fossa (near the apex of the orbit); but it can have several other causes.

The first symptom is typically diabetes mellitus, which is usually diagnosed around the age of 6. The next symptom to appear is often optic atrophy, the wasting of optic nerves, around the age of 11. The first signs of this are loss of colour vision and peripheral vision. The condition worsens over time, and people with optic atrophy are usually blind within 8 years of the first symptoms. Life expectancy of people suffering from this syndrome is about 30 years.

A mutation in the ZNHIT3 gene - a nuclear zinc finger protein involved in transcriptional regulation and in small nucleolar ribonucleoprotein particle assembly has been shown to be the cause of the Finnish-type of PEHO syndrome. However, the syndrome appear to be genetically heterogeneous and it might reflect an underlying genetic tubulinopathy, with biallelic mutations in the gene PRUNE1 also identified in non-Finnish patients with PEHO syndrome.

There is no known direct treatment. Current treatment efforts focus on managing the complications of Wolfram syndrome, such as diabetes mellitus and diabetes insipidus.

A link between increased ICP and altered sodium and water retention was suggested by a report in which 77% of IIH patients had evidence of peripheral edema and 80% with orthostatic retention of sodium and water. Impaired saline and water load excretions were noted in the upright position in IIH patients with orthostatic edema compared to lean and obese controls without IIH. However, the precise mechanisms linking orthostatic changes to IIH were not defined, and many IH patients do not have these sodium and water abnormalities. Astronauts are well known to have orthostatic intolerance upon reentry to gravity after long-duration spaceflight, and the dietary sodium on orbit is also known to be in excess of 5 grams per day in some cases. The Majority of the NASA cases did have high dietary sodium during their increment. The ISS program is working to decrease in-flight dietary sodium intake to less than 3 grams per day. Prepackaged foods for the International Space Station were originally high in sodium at 5300 mg/d. This amount has now been substantially reduced to 3000 mg/g as a result of NASA reformulation of over ninety foods as a conscious effort to reduce astronaut sodium intake.