Chronic progressive external ophthalmoplegia (CPEO), also known as progressive external ophthalmoplegia (PEO), is a type of eye disorder characterized by slowly progressive inability to move the eyes and eyebrows. It is often the only feature of mitochondrial disease, in which case the term CPEO may be given as the diagnosis. In other people suffering from mitochondrial disease, CPEO occurs as part of a syndrome involving more than one part of the body, such as Kearns-Sayre syndrome. Occasionally CPEO may be caused by conditions other than mitochondrial diseases.

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.

CPEO is a rare disease that may affect those of all ages, but typically manifests in the young adult years. CPEO is the most common manifestation of mitochondrial myopathy, occurring in an estimated two-thirds of all cases of mitochondrial myopathy. Patients typically present with ptosis (drooping eyelids). Other diseases like Graves' disease, myasthenia gravis and glioma that may cause an external ophthalmoplegia must be ruled out.

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.

There have been cases of improvement in extra-ocular movement with botulinum toxin injection.

Kearns–Sayre syndrome occurs spontaneously in the majority of cases. In some cases it has been shown to be inherited through mitochondrial, autosomal dominant, or autosomal recessive inheritance. There is no predilection for race or sex, and there are no known risk factors. As of 1992 there were only 226 cases reported in published literature.

Ophthalmoparesis can result from disorders of various parts of the eye and nervous system:

- Infection around the eye. Ophthalmoplegia is an important finding in orbital cellulitis.

- The orbit of the eye, including mechanical restrictions of eye movement, as in Graves disease.

- The muscle, as in progressive external ophthalmoplegia or Kearns-Sayre syndrome.

- The neuromuscular junction, as in myasthenia gravis.

- The relevant cranial nerves (specifically the oculomotor, trochlear, and abducens), as in cavernous sinus syndrome or raised intracranial pressure.

- The brainstem nuclei of these nerves, as in certain patterns of brainstem stroke such as Foville's syndrome.

- White matter tracts connecting these nuclei, as in internuclear ophthalmoplegia, an occasional finding in multiple sclerosis.

- Dorsal midbrain structures, as in Parinaud's syndrome.

- Certain parts of the cerebral cortex (including the frontal eye fields), as in stroke.

- Toxic envenomation by mambas, taipans, and kraits.

Thiamine deficiency can cause ophthalmoparesis in susceptible persons; this is part of the syndrome called Wernicke encephalopathy. The causal pathway by which this occurs is unknown. Intoxication with certain substances, such as phenytoin, can also cause ophthalmoparesis.

Ophthalmoparesis or ophthalmoplegia 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 ophthalmoplegia means involvement limited to the pupillary sphincter and ciliary muscle. External ophthalmoplegia refers to involvement of only the extraocular muscles. Complete ophthalmoplegia indicates involvement of both.

The disorder is caused by injury or dysfunction in the medial longitudinal fasciculus (MLF), a heavily myelinated tract that allows conjugate eye movement by connecting the paramedian pontine reticular formation (PPRF)-abducens nucleus complex of the contralateral side to the oculomotor nucleus of the ipsilateral side.

In young patients with bilateral INO, multiple sclerosis is often the cause. In older patients with one-sided lesions a stroke is a distinct possibility. Other causes are possible.

Kearns–Sayre syndrome (KSS) is a mitochondrial myopathy with a typical onset before 20 years of age. KSS is a more severe syndromic variant of chronic progressive external ophthalmoplegia (abbreviated CPEO), a syndrome that is characterized by isolated involvement of the muscles controlling movement of the eyelid (levator palpebrae, orbicularis oculi) and eye (extra-ocular muscles). This results in ptosis and ophthalmoplegia respectively. KSS involves a combination of the already described CPEO as well as pigmentary retinopathy in both eyes and cardiac conduction abnormalities. Other symptoms may include cerebellar ataxia, proximal muscle weakness, deafness, diabetes mellitus, growth hormone deficiency, hypoparathyroidism, and other endocrinopathies. In both of these diseases, muscle involvement may begin unilaterally but always develops into a bilateral deficit, and the course is progressive. This discussion is limited specifically to the more severe and systemically involved variant.

Parinaud's Syndrome results from injury, either direct or compressive, to the dorsal midbrain. Specifically, compression or ischemic damage of the mesencephalic tectum, including the superior colliculus adjacent oculomotor (origin of cranial nerve III) and Edinger-Westphal nuclei, causing dysfunction to the motor function of the eye.

Classically, it has been associated with three major groups:

1. Young patients with brain tumors in the pineal gland or midbrain: pinealoma (intracranial germinomas) are the most common lesion producing this syndrome.

2. Women in their 20s-30s with multiple sclerosis

3. Older patients following stroke of the upper brainstem

However, any other compression, ischemia or damage to this region can produce these phenomena: obstructive hydrocephalus, midbrain hemorrhage, cerebral arteriovenous malformation, trauma and brainstem toxoplasmosis infection. Neoplasms and giant aneurysms of the posterior fossa have also been associated with the midbrain syndrome.

Vertical supranuclear ophthalmoplegia has also been associated with metabolic disorders, such as Niemann-Pick disease, Wilson's disease, kernicterus, and barbiturate overdose.

The eye findings of Parinaud's Syndrome generally improve slowly over months, especially with resolution of the causative factor; continued resolution after the first 3–6 months of onset is uncommon. However, rapid resolution after normalization of intracranial pressure following placement of a ventriculoperitoneal shunt has been reported.

Treatment is primarily directed towards etiology of the dorsal midbrain syndrome. A thorough workup, including neuroimaging is essential to rule out anatomic lesions or other causes of this syndrome. Visually significant upgaze palsy can be relieved with bilateral inferior rectus recessions. Retraction nystagmus and convergence movement are usually improved with this procedure as well.

Internuclear ophthalmoplegia (INO) is a disorder of conjugate lateral gaze in which the affected eye shows impairment of adduction. When an attempt is made to gaze contralaterally (relative to the affected eye), the affected eye adducts minimally, if at all. The contralateral eye abducts, however with nystagmus. Additionally, the divergence of the eyes leads to horizontal diplopia. That is, if the right eye is affected the patient will "see double" when looking to the left, seeing two images side-by-side. Convergence is generally preserved.

The one and a half syndrome is a rare weakness in eye movement affecting both eyes, in which one cannot move laterally at all, and the other can move in only one lateral direction (inward or outward). More formally, it is characterized by ""a conjugate horizontal gaze palsy in one direction and an internuclear ophthalmoplegia in the other"". The most common manifestation of this unusual syndrome is limitation of horizontal eye movement to abduction (moving away from the midline) of one eye (e.g. right eye in the diagram on the right) with no horizontal movement of the other eye (e.g. left eye in the diagram on the right). Nystagmus is also present when the eye on the opposite side of the lesion is abducted. Convergence is classically spared as cranial nerve III (oculomotor nerve) and its nucleus is spared bilaterally.

The prognosis of a lesion in the visual neural pathways that causes a conjugate gaze palsy varies greatly. Depending on the nature of the lesion, recovery may happen rapidly or recovery may never progress. For example, optic neuritis, which is caused by inflammation, may heal in just weeks, while patients with an ischemic optic neuropathy may never recover.

Retinitis pigmentosa is the leading cause of inherited blindness, with approximately 1/4,000 individuals experiencing the non-syndromic form of their disease within their lifetime. It is estimated that 1.5 million people worldwide are currently affected. Early onset RP occurs within the first few years of life and is typically associated with syndromic disease forms, while late onset RP emerges from early to mid-adulthood.

Autosomal dominant and recessive forms of retinitis pigmentosa affect both male and female populations equally; however, the less frequent X-linked form of the disease affects male recipients of the X-linked mutation, while females usually remain unaffected carriers of the RP trait. The X-linked forms of the disease are considered severe, and typically lead to complete blindness during later stages. In rare occasions, a dominant form of the X-linked gene mutation will affect both males and females equally.

Due to the genetic inheritance patterns of RP, many isolate populations exhibit higher disease frequencies or increased prevalence of a specific RP mutation. Pre-existing or emerging mutations that contribute to rod photoreceptor degeneration in retinitis pigmentosa are passed down through familial lines; thus, allowing certain RP cases to be concentrated to specific geographical regions with an ancestral history of the disease. Several hereditary studies have been performed to determine the varying prevalence rates in Maine (USA), Birmingham (England), Switzerland (affects 1/7000), Denmark (affects 1/2500), and Norway. Navajo Indians display an elevated rate of RP inheritance as well, which is estimated as affecting 1 in 1878 individuals. Despite the increased frequency of RP within specific familial lines, the disease is considered non-discriminatory and tends to equally affect all world populations.

Although no cure currently exists, there is hope in treatment for this class of hereditary diseases with the use of an embryonic mitochondrial transplant.

There is no treatment of conjugate gaze palsy itself, so the disease or condition causing the gaze palsy must be treated, likely by surgery. As stated in the causes section, the gaze palsy may be due to a lesion caused by stroke or a condition. Some of the conditions such as Progressive supra nuclear palsy are not curable, and treatment only includes therapy to regain some tasks, not including gaze control. Other conditions such as Niemann-Pick disease type C have limited drug therapeutic options. Stroke victims with conjugate gaze palsies may be treated with intravenous therapy if the patent presents early enough, or with a surgical procedure for other cases.

Use of high doses of opioid drugs such as morphine, oxycodone, heroin, or hydrocodone can cause ptosis. Pregabalin (Lyrica), an anticonvulsant drug, has also been known to cause mild ptosis.

Mitochondrial myopathies are types of myopathies associated with mitochondrial disease. On biopsy, the muscle tissue of patients with these diseases usually demonstrate "ragged red" muscle fibers. These ragged-red fibers contain mild accumulations of glycogen and neutral lipids, and may show an increased reactivity for succinate dehydrogenase and a decreased reactivity for cytochrome c oxidase. Inheritance was believed to be maternal (non-Mendelian extranuclear). It is now known that certain nuclear DNA deletions can also cause mitochondrial myopathy such as the OPA1 gene deletion. There are several subcategories of mitochondrial myopathies.

RP may be:

(1) Non-syndromic, that is, it occurs alone, without any other clinical findings,

(2) Syndromic, with other neurosensory disorders, developmental abnormalities, or complex clinical findings, or

(3) Secondary to other systemic diseases.

- RP combined with deafness (congenital or progressive) is called Usher syndrome.

- Alport's syndrome is associated with RP and an abnormal glomerular-basement membrane leading nephrotic syndrome and inherited as X-linked dominant.

- RP combined with ophthalmoplegia, dysphagia, ataxia, and cardiac conduction defects is seen in the mitochondrial DNA disorder Kearns-Sayre syndrome (also known as Ragged Red Fiber Myopathy)

- RP combined with retardation, peripheral neuropathy, acanthotic (spiked) RBCs, ataxia, steatorrhea, is absence of VLDL is seen in abetalipoproteinemia.

- RP is seen clinically in association with several other rare genetic disorders (including muscular dystrophy and chronic granulomatous disease) as part of McLeod syndrome. This is an X-linked recessive phenotype characterized by a complete absence of XK cell surface proteins, and therefore markedly reduced expression of all Kell red blood cell antigens. For transfusion purposes these patients are considered completely incompatible with all normal and K0/K0 donors.

- RP associated with hypogonadism, and developmental delay with an autosomal recessive inheritance pattern is seen with Bardet-Biedl syndrome

Other conditions include neurosyphilis, toxoplasmosis and Refsum's disease.

Ptosis occurs due to dysfunction of the muscles that raise the eyelid or their nerve supply (oculomotor nerve for levator palpebrae superioris and sympathetic nerves for superior tarsal muscle). It can affect one eye or both eyes and is more common in the elderly, as muscles in the eyelids may begin to deteriorate. One can, however, be born with ptosis. Congenital ptosis is hereditary in three main forms. Causes of congenital ptosis remain unknown. Ptosis may be caused by damage/trauma to the muscle which raises the eyelid, damage to the superior cervical sympathetic ganglion or damage to the nerve (3rd cranial nerve (oculomotor nerve)) which controls this muscle. Such damage could be a sign or symptom of an underlying disease such as diabetes mellitus, a brain tumor, a pancoast tumor (apex of lung) and diseases which may cause weakness in muscles or nerve damage, such as myasthenia gravis or Oculopharyngeal muscular dystrophy. Exposure to the toxins in some snake venoms, such as that of the black mamba, may also cause this effect.

Ptosis can be caused by the aponeurosis of the levator muscle, nerve abnormalities, trauma, inflammation or lesions of the lid or orbit. Dysfunctions of the levators may occur as a result of autoimmune antibodies attacking and eliminating the neurotransmitter.

Ptosis may be due to a myogenic, neurogenic, aponeurotic, mechanical or traumatic cause and it usually occurs isolated, but may be associated with various other conditions, like immunological, degenerative, or hereditary disorders, tumors, or infections

Acquired ptosis is most commonly caused by aponeurotic ptosis. This can occur as a result of senescence, dehiscence or disinsertion of the levator aponeurosis. Moreover, chronic inflammation or intraocular surgery can lead to the same effect. Also, wearing contact lenses for long periods of time is thought to have a certain impact on the development of this condition.

Congenital neurogenic ptosis is believed to be caused by the Horner syndrome. In this case, a mild ptosis may be associated with ipsilateral ptosis, iris and areola hypopigmentation and anhidrosis due to the paresis of the Mueller muscle. Acquired Horner syndrome may result after trauma, neoplastic insult, or even vascular disease.

Ptosis due to trauma can ensue after an eyelid laceration with transection of the upper eyelid elevators or disruption of the neural input.

Other causes of ptosis include eyelid neoplasms, neurofibromas or the cicatrization after inflammation or surgery. Mild ptosis may occur with aging.

A drooping eyelid can be one of the first signals of a third nerve palsy due to a cerebral aneurysm, that otherwise is asymptomatic and referred to as an oculomotor nerve palsy.

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.

Congenital fibrosis of the extraocular muscles, or CFEOM, is a class of rare genetic disorders affecting one or more of the muscles that move the eyeballs. Individuals with CFEOM have varying degrees of ophthalmoplegia (an inability to move the eyes in one or more directions) and ptosis. The condition is present from birth and non-progressive, runs in families, and usually affects both eyes similarly. In the most common form, the superior recti are dysfunctional and the inferior recti, lacking proper opposition, pull the eyes down, forcing the head to be tilted upward in order to see straight ahead.

There are three types of CFEOM, numbered 1-3. CFEOM1, the most common type, is now known to be caused by one of several mutations in the KIF21A gene, while CFEOM2 is caused by mutations in the PHOX2A gene. CFEOM3 is caused by mutations in the TUBB3 gene.

CFEOM was first named in 1956, although papers describing conditions now known or assumed to be CFEOM appear in the medical literature as early as 1840. Due to its rarity, it has been independently cited numerous times under many different names.

The fact that some people affected with this disease have circulating antinuclear antibodies in their serum supports the theory that Parry–Romberg syndrome may be an autoimmune disease, specifically a variant of localized scleroderma. Several instances have been reported where more than one member of a family has been affected, prompting speculation of an autosomal dominant inheritance pattern. However, there has also been at least one report of monozygotic twins in which only one of the twins was affected, casting doubt on this theory. Various other theories about the cause and pathogenesis have been suggested, including alterations in the peripheral sympathetic nervous system (perhaps as a result of trauma or infection involving the cervical plexus or the sympathetic trunk), as the literature reported it following sympathectomy, disorders in migration of cranial neural crest cells, or chronic cell-mediated inflammatory process of the blood vessels. It is likely that the disease results from different mechanisms in different people, with all of these factors potentially being involved.