Concomitant esotropia – that is, an inward squint that does not vary with the direction of gaze – mostly sets in before 12 months of age (this constitutes 40% of all strabismus cases) or at the age of three or four. Most patients with "early-onset" concomitant esotropia are emmetropic, whereas most of the "later-onset" patients are hyperopic. It is the most frequent type of natural strabismus not only in humans, but also in monkeys.

Concomitant esotropia can itself be subdivided into esotropias that are ether "constant," or "intermittent."

- Constant esotropia

- Intermittent esotropia

A patient can have a constant esotropia for reading, but an intermittent esotropia for distance (but rarely vice versa).

Esotropias can be concomitant, where the size of the deviation does not vary with direction of gaze—or incomitant, where the direction of gaze does affect the size, or indeed presence, of the esotropia. The majority of esotropias are concomitant and begin early in childhood, typically between the ages of 2 to 4 years. Incomitant esotropias occur both in childhood and adulthood as a result of neurological, mechanical or myogenic problems affecting the muscles controlling eye movements.

Strabismus may also be classified based on time of onset, either congenital, acquired, or secondary to another pathological process. Many infants are born with their eyes slightly misaligned, and this is typically outgrown by six to 12 months of age. Acquired and secondary strabismus develop later. The onset of accommodative esotropia, an overconvergence of the eyes due to the effort of accommodation, is mostly in early childhood. Acquired non-accommodative strabismus and secondary strabismus are developed after normal binocular vision has developed. In adults with previously normal alignment, the onset of strabismus usually results in double vision.

Any disease that causes vision loss may also cause strabismus, but it can also result from any severe and/or traumatic injury to the affected eye. Sensory strabismus is strabismus due to vision loss or impairment, leading to horizontal, vertical or torsional misalignment or to a combination thereof, with the eye with poorer vision drifting slightly over time. Most often, the outcome is horizontal misalignment. Its direction depends on the patient age at which the damage occurs: patients whose vision is lost or impaired at birth are more likely to develop esotropia, whereas patients with acquired vision loss or impairment mostly develop exotropia. In the extreme, complete blindness in one eye generally leads to the blind eye reverting to an anatomical position of rest.

Although many possible causes of strabismus are known, among them severe and/or traumatic injuries to the afflicted eye, in many cases no specific cause can be identified. This last is typically the case when strabismus is present since early childhood.

Results of a U.S. cohort study indicate that the incidence of adult-onset strabismus increases with age, especially after the sixth decade of life, and peaks in the eighth decade of life, and that the lifetime risk of being diagnosed with adult-onset strabismus is approximately 4%.

When observing a person with strabismus, the misalignment of the eyes may be quite apparent. A patient with a constant eye turn of significant magnitude is very easy to notice. However, a small magnitude or intermittent strabismus can easily be missed upon casual observation. In any case, an eye care professional can conduct various tests, such as cover testing, to determine the full extent of the strabismus.

Symptoms of strabismus include double vision and/or eye strain. To avoid double vision, the brain may adapt by ignoring one eye. In this case, often no noticeable symptoms are seen other than a minor loss of depth perception. This deficit may not be noticeable in someone who has had strabismus since birth or early childhood, as they have likely learned to judge depth and distances using monocular cues. However, a constant unilateral strabismus causing constant suppression is a risk for amblyopia in children. Small-angle and intermittent strabismus are more likely to cause disruptive visual symptoms. In addition to headaches and eye strain, symptoms may include an inability to read comfortably, fatigue when reading, and unstable or "jittery" vision.

The earliest sign of exotropia is usually a noticeable outward deviation of the eye. This sign may at first be intermittent, occurring when a child is daydreaming, not feeling well, or tired. It may also be more noticeable when the child looks at something in the distance. Squinting or frequent rubbing of the eyes is also common with exotropia. The child probably will not mention seeing double, i.e., double vision. However, he or she may close one eye to compensate for the problem.

Generally, exotropia progresses in frequency and duration. As the disorder progresses, the eyes will start to turn out when looking at close objects as well as those in the distance. If left untreated, the eye may turn out continually, causing a loss of binocular vision.

In young children with any form of strabismus, the brain may learn to ignore the misaligned eye's image and see only the image from the best-seeing eye. This is called amblyopia, or lazy eye, and results in a loss of binocular vision, impairing depth perception. In adults who develop strabismus, double vision sometimes occurs because the brain has already been trained to receive images from both eyes and cannot ignore the image from the turned eye.

Additionally in adults who have had exotropia since childhood, the brain may adapt to using a "blind-spot" whereby it receives images from both eyes, but no full image from the deviating eye, thus avoiding double vision and in fact increasing peripheral vision on the side of the deviating eye.

Exotropia is a form of strabismus where the eyes are deviated outward. It is the opposite of esotropia and usually involves more severe axis deviation than exophoria. People with exotropia often experience crossed diplopia. Intermittent exotropia is a fairly common condition. "Sensory exotropia" occurs in the presence of poor vision. Infantile exotropia (sometimes called "congenital exotropia") is seen during the first year of life, and is less common than "essential exotropia" which usually becomes apparent several years later.

The brain's ability to see three-dimensional objects depends on proper alignment of the eyes. When both eyes are properly aligned and aimed at the same target, the visual portion of the brain fuses the forms into a single image. When one eye turns inward, outward, upward, or downward, two different pictures are sent to the brain. This causes loss of depth perception and binocular vision. There have also been some reports of people that can "control" their afflicted eye. The term is from Greek "exo" meaning "outward" and "trope" meaning "a turning".

Heterophoria is an eye condition in which the directions that the eyes are pointing at rest position, when "not" performing binocular fusion, are not the same as each other, or, "not straight". There can be esophoria, where the eyes tend to cross inward in the absence of fusion; exophoria, in which they diverge; or hyperphoria, in which one eye points up or down relative to the other. Phorias are known as 'latent squint' because the tendency of the eyes to deviate is kept latent by fusion. A person with two normal eyes has single vision (usually) because of the combined use of the sensory and motor systems. The motor system acts to point both eyes at the target of interest; any offset is detected visually (and the motor system corrects it). Heterophoria only occurs during dissociation of the left eye and right eye, when fusion of the eyes is absent. If you cover one eye (e.g. with your hand) you remove the sensory information about the eye's position in the orbit. Without this, there is no stimulus to binocular fusion, and the eye will move to a position of "rest". The difference between this position, and where it would be were the eye uncovered, is the heterophoria. The opposite of heterophoria, where the eyes are straight when relaxed and not fusing, is called orthophoria.

In contrast, fixation disparity is a very small deviation of the pointing directions of the eyes that is present while performing binocular fusion.

Heterophoria is usually asymptomatic. This is when it is said to be "compensated". When fusional reserve is used to compensate for heterophoria, it is known as compensating vergence. In severe cases, when the heterophoria is not overcome by fusional vergence, sign and symptoms appear. This is called decompensated heterophoria.

Heterophoria may lead to squint or also known as strabismus.

When the fusional vergence system can no longer hold back heterophoria, the phoria manifests. In this condition, the eyes deviate from the fixating position.

Pseudomyopia refers to an intermittent and temporary shift in refractive error of the eye towards myopia, in which the focusing of light in front of the retina is due to a transient spasm of the ciliary muscle causing an increase in the refractive power of the eye. It may be either organic, through stimulation of the parasympathetic nervous system, or functional in origin, through eye strain or fatigue of ocular systems. It is common in young adults who have active accommodation, and classically occurs after a change in visual requirements, such as students preparing for an exam, or a change in occupation.

The major symptom is intermittent blurring of distance vision particularly noticeable after prolonged periods of near work, and symptoms of asthenopia. The vision may clear temporarily using concave (minus) lenses. The diagnosis is done by cycloplegic refraction using a strong cycloplegic like atropine or homatropine eye drops. Accommodative amplitude and facility may be reduced as a result of the ciliary muscle spasm.

Treatment is dependent on the underlying aetiology. Organic causes may include systemic or ocular medications, brain stem injury, or active ocular inflammation such as uveitis. Functional pseudomyopia is managed though modification of working conditions, an updated refraction, typically involving a reduction of a myopic prescription to some lower myopic prescription, or through appropriate ocular exercises.

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.

Optic nerve sheath meningiomas (ONSM) are rare benign tumors of the optic nerve. 60–70% of cases occur in middle age females, and is more common in older adults (mean age 44.7 years). It is also seen in children, but this is rare. The tumors grow from cells that surround the optic nerve, and as the tumor grows, it compresses the optic nerve. This causes loss of vision in the affected eye. Rarely, it may affect both eyes at the same time.

It is typically a slow growing tumor, and has never been reported to cause death. However, there is concern that the tumor can grow into the brain and cause other types of neurological damage. In some patients, the tumor grows so slowly that treatment is not necessary. Standard treatments are observation, surgery, radiation therapy, and combinations of the above.

Approximately 100 cases have been described in the literature to date.

The facial features are characteristic and include

- Deep set eyes

- Strabismus

- Myopia

- Marked nasal root

- Broad and/or beaked nasal bridge

- Prominent Cupid's bow

- Everted lower lip

- Tented upper lip

- Large mouth

- Widely spaced teeth

- Wide and shallow palate

- Ears with thick and overfolded helix

Most have a smiling appearance.

Intellectual disability is severe. Language is absent or limited to only a few words. Stereotypic movements particularly of the arms, wrists and fingers is almost universal. Hypotonia is common (75%) as is an unsteady gait. All have delayed walking. Other features include a single (simian) palmar crease, long, slender fingers, flat feet and cryptorchidism (in males). Finger clubbing and the presence of fetal pads is common. Hyperventilation occurs in over half and is frequently followed by apnea and cyanosis. During these episodes aerophagia may occur. Constipation is common. Microcephaly and seizures may occur. Hypopigmented skin macules have occasionally been reported.

Pitt–Hopkins syndrome is a rare genetic disorder characterized by developmental delay, a wide mouth, distinctive facial features, and intermittent hyperventilation followed by apnea. It is associated with an abnormality within chromosome 18: specifically, it is caused by an insufficient expression of the TCF4 gene.

Reflex seizures may occur in reflex epilepsies only or also in other epilepsy syndromes in combination with other seizure types. They are seizures which are the result of sensory stimulation caused by the environment or own activities of the affected persons. The most common type is photosensitive seizure.

In susceptible people, reflex seizures may be elicited by many stimuli including eating, hot water, intermittent visual stimuli (flickering, stroboscopic light), music, playing games, reading, writing, singing sudden noise, tooth brushing or touch at certain areas of the body.

A Spigelian hernia (or lateral ventral hernia) is a hernia through the Spigelian fascia, which is the aponeurotic layer between the rectus abdominis muscle medially, and the semilunar line laterally. These are generally interparietal hernias, meaning that they do not lie below the subcutaneous fat but penetrate between the muscles of the abdominal wall; therefore, there is often no notable swelling.

Spigelian hernias are usually small and therefore risk of strangulation is high. Most occur on the right side. (4th–7th decade of life.) Compared to other types of hernias they are rare.

Patients typically present with either an intermittent mass, localized pain, or signs of bowel obstruction. Ultrasonography or a CT scan can establish the diagnosis, although CT scan provides the greatest sensitivity and specificity.

Strictures tend to be diagnosed based on difficulty with insertion and manipulation during sialendoscopy, or by sialography or ultrasound.

Levator ani syndrome is a condition characterized by brief intermittent burning pain or tenesmus of the rectal or perineal area.

Intermittent hair–follicle dystrophy is a disorder of the hair follicle leading to increased fragility of the shaft, with no identifiable biochemical disturbance, also with an unknown prevalence.

DES manifests as intermittent difficulty swallowing (dysphagia) for solid foods and liquids, and atypical chest pain. The chest pain may appear similar to cardiac chest pain (angina pectoris), so investigating the possible existence of heart disease is often indicated.

Salivary duct stricture (also termed salivary duct stenosis) is narrowing of the duct of a major salivary gland.

The hallmark sign of urethral stricture is a weak urinary stream. Other symptoms include:

- Splaying of the urinary stream

- Urinary frequency

- Urinary urgency

- Straining to urinate

- Pain during urination

- Urinary tract infection

- Prostatitis

- Inability to completely empty the bladder.

Some patients with severe urethral strictures are completely unable to urinate. This is referred to as acute urinary retention, and is a medical emergency. Hydronephrosis and renal failure may also occur.

Diffuse esophageal spasm (DES) is a condition characterized by uncoordinated contractions of the esophagus, which may cause difficulty swallowing (dysphagia) or regurgitation. In some cases, it may cause symptoms such as chest pain, similar to heart disease. The cause of DES remains unknown.

Certain abnormalities on x-ray imaging are commonly observed in DES, such as a "corkscrew" or "rosary bead esophagus", although these findings are not unique to this condition. Specialized testing called manometry can be performed to evaluate the motor function of the esophagus, which can help identify abnormal patterns of muscle contraction within the esophagus that are suggestive of DES. The treatment of DES consists primarily of medications, such as acid suppressing agents (like proton pump inhibitors), calcium channel blockers, hyoscine butylbromide, or nitrates. In only extremely rare cases, surgery may be considered. People with DES have higher incidences of gastroesophageal reflux disease (GERD) and anxiety.

Geniculate ganglionitis or geniculate neuralgia (GN), also called nervus intermedius neuralgia, Ramsay Hunt syndrome, or Hunt's neuralgia, is a rare disorder characterized by severe paroxysmal neuralgic pain deep in the ear, that may spread to the ear canal, outer ear, mastoid or eye regions. GN may also occur in combination with trigeminal or glossopharyngeal neuralgia.

The pain of GN is sharp, shooting or burning and can last for hours. Painful attacks can be triggered by cold, noise, swallowing or touch, but triggers are usually unique to the sufferer. Other related symptoms that may be experienced include increased salivation, bitter taste, tinnitus and vertigo.

GN is rare, and only limited data is available regarding the incidence, prevalence, and risk factors associated with this condition. Middle-aged adults, however, seem to be predominantly affected, women more than men.

GN may be caused by compression of somatic sensory branch of cranial nerve VII which goes through the nervus intermedius. In sufferers of GN, signals sent along these nerves are altered and interpreted by the geniculate ganglion (a structure in the brain) as GN pain. GN may also develop following herpes zoster oticus (Ramsay Hunt syndrome), where cold sores occur on the ear drum or ear. This may also be associated with facial paresis (weakness), tinnitus, vertigo and deafness. Disorders of lacrimation, salivation and/or taste sometimes accompany the pain. There is a common association with herpes zoster.

Dyssomnias are a broad classification of sleeping disorders involving difficulty getting to sleep, remaining asleep, or of excessive sleepiness.

Dyssomnias are primary disorders of initiating or maintaining sleep or of excessive sleepiness and are characterized by a disturbance in the amount, quality, or timing of sleep.

Patients may complain of difficulty getting to sleep or staying asleep, intermittent wakefulness during the night, early morning awakening, or combinations of any of these. Transient episodes are usually of little significance. Stress, caffeine, physical discomfort, daytime napping, and early bedtimes are common factors.