A simple definition of the syndrome is "limited elevation in adduction from mechanical causes around the superior oblique". This definition indicates that when the head is upright, the eye is restricted in movement due to problems with muscles and tendons that surround the eye.

Harold W. Brown characterized the syndrome in many ways such as:

- Limited elevation in the eye when head is straight up

- Eyes point out in a straight up gaze (divergence in up gaze)

- Widening of the eyelids in the affected eye on adduction

- Head tilts backwards (compensatory chin elevation to avoid double vision)

- Near normal elevation in abduction

He concluded that all of these features of Brown syndrome were due to the shortening or tightening of the anterior superior oblique tendon. Because this syndrome can be acquired or occur at random and has spontaneous resolution, Brown hypothesized one major truth for this disorder — that the short tendon sheath was due to a complete separation, congenital paresis, of the ipsilateral (on the same side) inferior oblique muscle and secondary to a permanent shortening.

After further research, he redefined the sheath syndrome into the following divisions: true sheath syndrome, which categorized only the cases that had a congenital short anterior sheath of the superior oblique tendon, and simulated sheath syndrome, which characterized all cases in which the clinical features of a sheath syndrome caused by something different other than a congenital short anterior sheath of the tendon. The clinical features of the two categories are correct but true sheath syndrome is always congenital. However, in 1970 it was discovered that a tight sheath tendon was not the cause of Brown's Syndrome. The real cause was a tight or short superior oblique tendon; studies have confirmed this and have labeled the tendon inelastic.

Brown's syndrome can be divided in two categorizes based on the restriction of movement on the eye itself and how it affects the eye excluding the movement:

- Congenital (present at birth) Brown's syndrome results from structural anomalies other than a short tendon sheath but other fibrous adhesions may be present around the trochlear area.

- Acquired cases arise from trauma, surgery, sinusitis and inflammation of the superior oblique tendon sheath in rheumatoid arthritis. Orbital floor fractures may trap the orbital tissue in such a way as to simulate Brown's syndrome. Intermittent forms of vertical retraction syndrome have been associated with click, which occurs as the restriction is released (superior oblique click syndrome).

Affected individuals typically experience limited relief from standard pain relieving medication, with the exception of some neuroleptic agents. Patients frequently experience 'pseudovisceral' phenomena or symptoms of altered autonomic nervous system function including nausea, bloating, abdominal swelling, loss of appetite with consecutively lowered body weight or an altered defecation process.

Pain is typically related to tensing the abdominal wall muscles, so any type of movement is prone to aggravate pain. Lying quietly can be the least painful position. Most patients report that they cannot sleep on the painful side.

Anterior cutaneous nerve entrapment syndrome (ACNES) is a nerve entrapment condition that causes chronic pain of the abdominal wall. It occurs when nerve endings of the lower thoracic intercostal nerves (7–12) are 'entrapped' in abdominal muscles, causing a severe localized nerve (neuropathic) pain that is usually experienced at the front of the abdomen.

ACNES syndrome is frequently overlooked and unrecognized, although the incidence is estimated to be 1:2000 patients.

The relative unfamiliarity with this condition often leads to significant diagnostic delays and misdiagnoses, often resulting in unnecessary diagnostic interventions and futile procedures. Physicians often misdiagnose ACNES as irritable bowel syndrome or "functional disorders", as symptoms of the condition are not dispositive.

Stenosing tenosynovitis often presents with a painful and swollen thumb with limited range of motion, or a ring finger or middle finger with similarly limited motion. There is often a feeling of catching when the thumb is flexed. In the ring and middle fingers, often a nodule can be felt when you press the area of the hand where the palm meets the finger.

Symptoms are pain at the radial side of the wrist, spasms, tenderness, occasional burning sensation in the hand, and swelling over the thumb side of the wrist, and difficulty gripping with the affected side of the hand. The onset is often gradual. Pain is made worse by movement of the thumb and wrist, and may radiate to the thumb or the forearm.

The primary vitreous used in formation of the eye during fetal development remains in the eye upon birth and is hazy and scarred. The symptoms are leukocoria, strabismus, nystagmus and blurred vision, blindness.

BVVL is marked by a number of cranial nerve palsies, including those of the motor components involving the 7th and 9th-12th cranial nerves, spinal motor nerves, and upper motor neurons. Major features of BVVL include facial and neck weakness, fasciculation of the tongue, and neurological disorders from the cranial nerves. The neurological manifestations develop insidiously: they usually begin with sensorineural deafness, progress inexorably to paralysis, and often culminate in respiratory failure. Most mortality in patients has been from either respiratory infections or respiratory muscle paralysis. Pathological descriptions of BVVL include injury and depletion of 3rd-7th cranial nerves, loss of the spinal anterior horn cells, degeneration of Purkinje cells, as well as degeneration of the spinocerebellar and pyramidal tracts. The first symptoms in nearly all cases of BVVL is progressive vision loss and deafness, and the first initial symptoms are seen anywhere from one to three years.

Most cases of deafness are followed by a latent period that can extend anywhere from weeks to years, and this time is usually marked by cranial nerve degeneration. Neurological symptoms of BVVL include optic atrophy, cerebellar ataxia, retinitis pigmentosa, epilepsy and autonomic dysfunction. Non-neurological symptoms can include diabetes, auditory hallucinations, respiratory difficulties, color blindness, and hypertension.

The radial nerve is one of the major nerves of the upper limb. It innervates all of the muscles in the extensor compartments of the arm. Injury to the nerve can therefore result in significant functional deficit for the individual. It is vulnerable to injury with fractures of the humeral shaft as it lies in very close proximity to the bone (it descends within the spiral groove on the posterior aspect of the humerus). Characteristic findings following injury will be as a result of radial nerve palsy (e.g. weakness of wrist/finger extension and sensory loss over the dorsum of the hand).

The vast majority of radial nerve palsies occurring as a result of humeral shaft fractures are neuropraxias (nerve conduction block as a result of traction or compression of the nerve), these nerve palsies can be expected to recover over a period of months. A minority of palsies occur as a result of more significant axonotmeses (division of the axon but preservation of the nerve sheath) or the even more severe neurotmeses (division of the entire nerve structure). As a result, it is important for individuals sustaining a Holstein–Lewis injury to be carefully followed up as if there is no evidence of return of function to the arm after approximately three months, further investigations and possibly, nerve exploration or repair may be required. The exception to this rule is if the fracture to the humerus requires fixing in the first instance. In that case, the nerve should be explored at the same time that fixation is performed.

Stenosing tenosynovitis (also known as trigger finger or trigger thumb) is a painful condition caused by the inflammation (tenosynovitis) and progressive restriction of the superficial and deep flexors fibrous tendon sheath adjacent to the A1 pulley at a metacarpal head. Repetitive forceful compression, tensile stress, and resistive flexion, causes inflammation, swelling, and microtrauma, that results in thickening (commonly a nodular formation) of the tendon distal to the pulley and stenosis of the tendon sheath leading to a painful digital base, limitation of finger movements, triggering, snapping, locking, and deformity progressively.

Patients report a popping sound at the proximal interphalangeal joint (PIP), morning stiffness with/without triggering, delayed and sometimes painful extension of the digit, and when more advanced, a locking position that requires manipulation to extend the affected finger. This condition more commonly affects the middle and ring fingers (occasionally the thumb), and the flexor rather than extensor tendons in the hand.

In rheumatic trigger finger (or in diabetes), more than one finger may be involved. Cases of stenosing peroneal tenosynovitis, have been reported where the patient presents with pain over the lateral malleolus, both with active and passive range of motion and no physical of radiographic evidence of instability.

Causes a ‘white reflex’ in the affected eye (leukocoria), prompting further investigation.

Trigger fingers is a common disorder characterized by catching, snapping or locking of the involved finger flexor tendon, associated with dysfunction and pain. It is a sub-set of stenosing tenosynovitis.

A disparity in size between the flexor tendon and the surrounding retinacular pulley system, most commonly at the level of the first annular (A1) pulley, results in difficulty flexing or extending the finger and the "triggering" phenomenon. The label of trigger finger is used because when the finger unlocks, it pops back suddenly, as if releasing a trigger on a gun.

A Holstein–Lewis fracture is a fracture of the distal third of the humerus resulting in entrapment of the radial nerve.

Nearly all individuals show multiple café au lait spots.Features common in neurofibromatosis - Lisch nodules, bone abnormalities, neurofibromas, optic pathway gliomas and malignant peripheral nerve sheath tumors - are absent in this condition Symptoms however, may include:

- Freckles

- Lipomas

- Macrocephaly

- Learning disabilities

- ADHD

- Developmental delay

Brown-Vialetto-Van-Laere syndrome (BVVL), sometimes known as Brown's Syndrome, is a rare degenerative disorder often initially characterized by progressive sensorineural deafness.

The syndrome most often affects children, adolescents, and young adults. As knowledge of BVVL grows some adult patients have now been diagnosed. There is no known cure, however with prompt treatment the prognosis may be positive with some patients stabilizing and even minor improvements noted in certain cases.

Bicipital tenosynovitis is tendinitis or inflammation of the tendon and sheath lining of the biceps muscle. It is often the result of many years of small tears or other degenerative changes in the tendon first manifesting in middle age, but can be due to a sudden injury. Calcification of the tendon, and osteophytes ("bone spurs") in the intertubercular groove can be apparent on x-rays. The condition (which can also occur in dogs) is commonly treated with physical therapy and cortisone and/or surgery.

Symptoms of the Roussy–Lévy syndrome mainly stem from nerve damage and the resulting progressive muscle atrophy. Neurological damage may result in absent tendon reflexes (areflexia), some distal sensory loss and decreased excitability of muscles to galvanic and faradic stimulation. Progressive muscle wasting results in weakness of distal limb muscles (especially the peronei), gait ataxia, pes cavus, postural tremors and static tremor of the upper limbs, kyphoscoliosis, and foot deformity.

These symptoms frequently translate into delayed onset of ability to walk, loss of coordination and balance, foot drop, and foot-bone deformities. They are usually first observed during infancy or early childhood, and slowly progress until about age 30, at which point progression may stop in some individuals, or symptoms may continue to slowly progress.

Diagnosis is made almost exclusively by history and physical examination alone. More than one finger may be affected at a time, though it usually affects the index, thumb, middle, or ring finger. The triggering is usually more pronounced late at night and into the morning, or while gripping an object firmly.

According to guidelines set forth by the Space Medicine Division, all long-duration astronauts with postflight vision changes should be considered a suspected case of VIIP syndrome. Each case could then be further differentiated by definitive imaging studies establishing the postflight presence of optic-disc edema, increased ONSD and altered OCT findings. The results from these imaging studies are then divided into five classes that determine what follow-up testing and monitoring is required.

De Quervain syndrome is diagnosed clinically, based on history and physical examination, though diagnostic imaging such as x-ray may be used to rule out fracture, arthritis, or other causes, based on the patient's history and presentation. Finkelstein's test is a physical exam maneuver used to diagnose de Quervain syndrome. To perform the test, the examiner grasps the thumb and sharply deviates the hand toward the ulnar side. If sharp pain occurs along the distal radius (top of forearm, about an inch below the wrist), de Quervain's syndrome is likely. While a positive Finkelstein's test is often considered pathognomonic for de Quervain syndrome, the maneuver can also cause pain in those with osteoarthritis at the base of the thumb.

Differential diagnoses include:

1. Osteoarthritis of the first carpo-metacarpal joint

2. Intersection syndrome—pain will be more towards the middle of the back of the forearm and about 2–3 inches below the wrist

3. Wartenberg's syndrome

The most common symptom of ONSM is a gradual loss of vision in one eye. In a minority of patients this may be intermittent, at least to begin with. Less common symptoms include pain in the affected eye, protrusion of the eye, or double vision.

Symptoms of CMT usually begin in early childhood or early adulthood, but can begin later. Some people do not experience symptoms until their early thirties or forties. Usually, the initial symptom is foot drop early in the course of the disease. This can also cause hammer toe, where the toes are always curled. Wasting of muscle tissue of the lower parts of the legs may give rise to a "stork leg" or "inverted champagne bottle" appearance. Weakness in the hands and forearms occurs in many people as the disease progresses.

Loss of touch sensation in the feet, ankles and legs, as well as in the hands, wrists and arms occur with various types of the disease. Early and late onset forms occur with 'on and off' painful spasmodic muscular contractions that can be disabling when the disease activates. High-arched feet (pes cavus) or flat-arched feet (pes planus) are classically associated with the disorder. Sensory and proprioceptive nerves in the hands and feet are often damaged, while unmyelinated pain nerves are left intact. Overuse of an affected hand or limb can activate symptoms including numbness, spasm, and painful cramping.

Symptoms and progression of the disease can vary. Involuntary grinding of teeth as well as squinting are prevalent and often go unnoticed by the person affected. Breathing can be affected in some; so can hearing, vision, as well as the neck and shoulder muscles. Scoliosis is common, causing hunching and loss of height. Hip sockets can be malformed. Gastrointestinal problems can be part of CMT, as can difficulty chewing, swallowing, and speaking (due to atrophy of vocal cords). A tremor can develop as muscles waste. Pregnancy has been known to exacerbate CMT, as well as severe emotional stress. Patients with CMT must avoid periods of prolonged immobility such as when recovering from a secondary injury as prolonged periods of limited mobility can drastically accelerate symptoms of CMT.

Pain due to postural changes, skeletal deformations, muscle fatigue and cramping is fairly common in people with CMT. It can be mitigated or treated by physical therapies, surgeries, and corrective or assistive devices. Analgesic medications may also be needed if other therapies do not provide relief from pain. Neuropathic pain is often a symptom of CMT, though, like other symptoms of CMT, its presence and severity varies from case to case. For some people, pain can be significant to severe and interfere with daily life activities. However, pain is not experienced by all people with CMT. When neuropathic pain is present as a symptom of CMT, it is comparable to that seen in other peripheral neuropathies, as well as postherpetic neuralgia and complex regional pain syndrome, among other diseases.

Optic-disc edema will be graded based on the Frisén Scale as below:

Stage 0 - Normal Optic-disc

Blurring of nasal, superior and inferior poles in inverse proportion to disc diameter. Radial nerve fiber layer (NFL) without NFL tortuosity. Rare obscuration of a major blood vessel, usually on the upper pole.

Stage 1 - Very Early Optic-disc Edema

Obscuration of the nasal border of the disc. No elevation of the disc borders. Disruption of the normal radial NFL arrangement with grayish opacity accentuating nerve fiber layer bundles. Normal temporal disc margin. Subtle grayish halo with temporal gap (best seen with indirect ophthalmoscopy). Concentric or radial retrochoroidal folds.

Stage 2 - Early Optic-disc Edema

Obscuration of all borders. Elevation of the nasal border. Complete peripapillary halo.

Stage 3 - Moderate Optic-disc Edema

Obscurations of all borders. Increased diameter of ONH. Obscuration of one or more segments of major blood vessels leaving the disc. Peripapillary halo - irregular outer fringe with finger-like extensions.

Stage 4 - Marked Optic-disc Edema

Elevation of the entire nerve head. Obscuration of all borders. Peripapillary halo. Total obscuration on the disc of a segment of a major vessel.

Stage 5 - Severe Optic-disc Edema

Dome-shaped protrusions representing anterior expansion of the ONG. Peripapillary halo is narrow and smoothly demarcated. Total obscuration of a segment of a major blood vessel may or may not be present. Obliteration of the optic cup.

Neurotmesis (in Greek tmesis signifies "to cut") is part of Seddon's classification scheme used to classify nerve damage. It is the most serious nerve injury in the scheme. In this type of injury, both the nerve and the nerve sheath are disrupted. While partial recovery may occur, complete recovery is impossible.

Peripheral nerve injuries can be classified in two different ways. Neurotmesis is classified under the Seddon system which is defined by three grades of nerve injury. The mildest grade is referred to as neurapraxia and is characterized by a reduction or complete blockage of conduction across a segment of nerve while axonal continuity is maintained and nerve conduction is preserved. These injuries are almost always reversed and a recovery takes place within days or weeks. The second classification of the Seddon system is referred to as axonotmesis which is a more severe case of peripheral nerve injury. Axonotmesis is classified by an interruption of the axons, but a preservation of the surrounding connective tissues around the axon. These injuries can heal themselves at about 1mm/day, therefore resulting in recovery to be possible but at a slower rate than neurapraxia. The last and most severe case of peripheral nerve injury is known as neurotmesis, which in most cases cannot be completely recovered from even with surgical repair.

The second classification of nerve injury is known as the Sunderland classification which is more complex and specific. This classification uses five different degrees of nerve injury, the first one being the least severe and the equivalent to neurapraxia and the most severe being the fifth degree and having the same classification as neurotmesis. The second through fourth degrees are dependent on the variance of axon discontinuity and are classified under Seddon’s classification of axonotmesis.