The term "cat eye" syndrome was coined because of the particular appearance of the vertical colobomas in the eyes of some patients. However, over half of the CES patients in the literature do not present with this trait.

The additional chromosome 22 usually arises spontaneously. It may be hereditary and parents may be mosaic for the marker chromosome but show no phenotypic symptoms of the syndrome.

The chromosomal area included in the cat eye syndrome "critical region" is 22pter→q11.

The characteristic features of the syndrome are:

- Limitation of abduction (outward movement) of the affected eye.

- Less marked limitation of adduction (inward movement) of the same eye.

- Retraction of the eyeball into the socket on adduction, with associated narrowing of the palpebral fissure (eye closing).

- Widening of the palpebral fissure on attempted abduction. (N. B. Mein and Trimble point out that this is "probably of no significance" as the phenomenon also occurs in other conditions in which abduction is limited.)

- Poor convergence.

- A head turn to the side of the affected eye to compensate for the movement limitations of the eye(s) and to maintain binocular vision.

While usually isolated to the eye abnormalities, Duane syndrome can be associated with other problems including cervical spine abnormalities Klippel-Feil syndrome, Goldenhar syndrome, heterochromia, and congenital deafness.

The presence of a small eye within the orbit can be a normal incidental finding but in most cases it is abnormal and results in blindness. The incidence is 14 per 100,000 and the condition affects 3-11% of blind children.

Microphthalmia (Greek: μικρός "micros" = small; ὀφθαλμός "ophthalmos" = eye), also referred as microphthalmos, is a developmental disorder of the eye in which one (unilateral microphthalmia) or both (bilateral microphthalmia) eyes are abnormally small and have anatomic malformations. It is different from nanophthalmos in which the eye is small in size but has no anatomical alterations.

An alternative name of the condition, LEOPARD syndrome, is a mnemonic, originally coined in 1969, as the condition is characterized by some of the following seven conditions, the first letters of which spell LEOPARD, along with the characteristic "freckling" of the skin, caused by the lentigines that is reminiscent of the large cat.

- Lentigines — Reddish-brown to dark brown macules (surface skin lesion) generally occurring in a high number (10,000+) over a large portion of the skin, at times higher than 80% coverage. These can even appear inside the mouth (buccal), or on the surface of the eye (scleral). These have irregular borders and range in size from 1 mm in diameter to café-au-lait spots, several centimeters in diameter. Also, some areas of vitiligo-like hypopigmentation may be observed.

- Electrocardiographic conduction abnormalities: Generally observed on an electrocardiograph as a bundle branch block.

- Ocular hypertelorism: Wideset eyes, which lead to a similar facial resemblance between patients. Facial abnormalities are the second highest occurring symptom after the lentigines. Abnormalities also include: broad nasal root, prognathism (protruding lower jaw), or low-set, possibly rotated, ears.

- Pulmonary stenosis: Narrowing of the pulmonary artery as it exits the heart. Other cardiac abnormalities may be present, including aortic stenosis, or mitral valve prolapse.

- Abnormal genitalia: usually cryptorchidism (retention of testicles in body) or monorchism (single testicle). In female patients, this presents as missing or single ovaries, much harder by nature to detect. Ultrasound imaging is performed at regular intervals, from the age of 1 year, to determine if ovaries are present.

- Retarded growth: Slow, or stunted growth. Most newborns with this syndrome are of normal birth weight and length, but will often slow within the first year.

- Deafness: Sensorineural (nerve deafness).

The presence of all of these hallmarks is not needed for a diagnosis. A clinical diagnosis is considered made when, with lentigines present there are 2 other symptoms observed, such as ECG abnormalities and ocular hypertelorism, or without lentigines, 3 of the above conditions are present, with a first-degree relative (i.e. parent, child, sibling) with a clinical diagnosis.

- Additional dermatologic abnormalities (axillary freckling, localized hypopigmentation, interdigital webbing, hyperelastic skin)

- Mild mental retardation is observed in about 30% of those affected with the syndrome

- Nystagmus (involuntary eye movements), seizures, or hyposmia (reduced ability to smell) has been documented in a few patients

- In 2004, a patient was reported with recurrent upper extremity aneurysms that required surgical repairs.

- In 2006, a NSML patient was reported with acute myelogenous leukemia.

Due to the rarity of the syndrome itself, it is hard to determine whether certain additional diseases are actually part of the syndrome. With a base population of possibly less than one thousand individuals, one or two outlying cases can skew the statistical population very quickly.

In the clinical setting, the principal difficulties in differential diagnosis arise as a consequence of the very early age at which patients with this condition first present. The clinician must be persistent in examining abduction and adduction, and in looking for any associated palpebral fissure changes or head postures, when attempting to determine whether what often presents as a common childhood squint (note-"squint" is a British term for two eyes not looking in the same direction) is in fact Duane syndrome. Fissure changes, and the other associated characteristics of Duane's such as up or down shoots and globe retraction, are also vital when deciding whether any abduction limitation is the result of Duane's and not a consequence of VI or abducens cranial nerve palsy.

Acquired Duane's syndrome is a rare event occurring after peripheral nerve palsy.

The syndrome is defined as the following changes:

- optic atrophy in the ipsilateral eye

- disc edema in the contralateral eye

- central scotoma (loss of vision in the middle of the visual fields) in the ipsilateral eye

- anosmia (loss of smell) ipsilaterally

This syndrome is due to optic nerve compression, olfactory nerve compression, and increased intracranial pressure (ICP) secondary to a mass (such as meningioma or plasmacytoma, usually an olfactory groove meningioma). There are other symptoms present in some cases such as nausea and vomiting, memory loss and emotional lability (i.e., frontal lobe signs).

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).

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.

The effects a coloboma has on the vision can be mild or more severe depending on the size and location of the gap. If, for example, only a small part of the iris is missing, vision may be normal, whereas if a large part of the retina or optic nerve is missing, vision may be poor and a large part of the visual field may be missing. This is more likely to cause problems with mobility if the lower visual field is absent. Other conditions can be associated with a coloboma. Sometimes, the eye may be reduced in size, a condition called microphthalmia. Glaucoma, nystagmus, scotoma, or strabismus may also occur.

Other ocular malformations that include coloboma or are related to it:

- CHARGE syndrome, a term that came into use as an acronym for the set of unusual congenital features seen in a number of newborn children. The letters stand for: coloboma of the eye, heart defects, atresia of the nasal choanae, retardation of growth and/or development, genital and/or urinary abnormalities, and ear abnormalities and deafness. Although these features are no longer used in making a diagnosis, the name has remained.

- Cat eye syndrome, caused by the short arm (p) and a small section of the long arm (q) of human chromosome 22 being present three (trisomic) or four times (tetrasomic) instead of the usual two times. The term "cat eye" was coined because of the particular appearance of the vertical colobomas in the eyes of some patients.

- Patau syndrome (trisomy 13), a chromosomal abnormality that can cause a number of deformities, some of which include structural eye defects, including microphthalmia, Peters anomaly, cataract, iris and/or fundus coloboma, retinal dysplasia or retinal detachment, sensory nystagmus, cortical visual loss, and optic nerve hypoplasia.

- Treacher Collins syndrome, autosomal dominant syndrome caused by mutation of "TCOF1". Coloboma is part of a set of characteristic facies that features craniofacial malformations, such as downslanting eyes, ear anomalies, or hypoplasia of zygomatic bone and jaw (micrognathia).

The syndrome gets its name from the characteristic cry of affected infants, which is similar to that of a meowing kitten, due to problems with the larynx and nervous system. About 1/3 of children lose the cry by age of 2 years. Other symptoms of cri du chat syndrome may include:

- feeding problems because of difficulty in swallowing and sucking;

- low birth weight and poor growth;

- severe cognitive, speech, and motor delays;

- behavioral problems such as hyperactivity, aggression, outbursts, and repetitive movements;

- unusual facial features which may change over time;

- excessive drooling;

- small head and jaw;

- wide eyes;

- skin tags in front of eyes.

Other common findings include hypotonia, microcephaly, growth retardation, a round face with full cheeks, hypertelorism, epicanthal folds, down-slanting palpebral fissures, strabismus, flat nasal bridge, down-turned mouth, micrognathia, low-set ears, short fingers, single palmar creases, and cardiac defects (e.g., ventricular septal defect [VSD], atrial septal defect [ASD], patent ductus arteriosus [PDA], tetralogy of Fallot). Infertility is not associated with Cri du chat.

It has also been observed that people with the condition have difficulties communicating. While levels of proficiency can range from a few words to short sentences, it is often recommended by medical professionals for the child to undergo some sort of speech therapy/aid with the help of a professional.

Less frequently encountered findings include cleft lip and palate, preauricular tags and fistulas, thymic dysplasia, intestinal malrotation, megacolon, inguinal hernia, dislocated hips, cryptorchidism, hypospadias, rare renal malformations (e.g., horseshoe kidneys, renal ectopia or agenesis, hydronephrosis), clinodactyly of the fifth fingers, talipes equinovarus, pes planus, syndactyly of the second and third fingers and toes, oligosyndactyly, and hyperextensible joints. The syndrome may also include various dermatoglyphics, including transverse flexion creases, distal axial triradius, increased whorls and arches on digits, and a single palmar crease.

Late childhood and adolescence findings include significant intellectual disability, microcephaly, coarsening of facial features, prominent supraorbital ridges, deep-set eyes, hypoplastic nasal bridge, severe malocclusion, and scoliosis.

Affected females reach puberty, develop secondary sex characteristics, and menstruate at the usual time. The genital tract is usually normal in females except for a report of a bicornuate uterus. In males, testes are often small, but spermatogenesis is thought to be normal.

Knobloch syndrome is a rare genetic disorder presenting severe eyesight problems and often a defect in the skull. It was named after W.H. Knobloch, who first described the syndrome in 1971. A usual occurrence is a degeneration of the vitreous humour and the retina, two components of the eye. This breakdown often results in the separation of the retina (the light-sensitive tissue at the back of the eye) from the eye, called retinal detachment, which can be recurrent. Extreme myopia (near-sightedness) is a common feature. The limited evidence available from electroretinography suggests a cone-rod pattern of dysfunction is also a feature.

Knobloch syndrome is caused by mutations in an autosomal recessive inherited gene. These mutations have been found in the COL18A1 gene that instructs for the formation of a protein that builds collagen XVIII. This type of collagen is found in the basement membranes of various body tissues. Its deficiency in the eye is thought to be responsible for affecting normal eye development. There are two types of Knobloch syndrome and the case has been made for a third.

When caused by mutations in the COL18A1 gene it is called Knobloch syndrome type 1. The genes causing types II and III have yet to be identified.

Knobloch syndrome is also characterised by cataracts, dislocated lens with skull defects such as occipital encephalocele and occipital aplasia. Encephalocele is a neural tube defect where the skull has not completely closed and sac-like protrusions of the brain can push through the skull; (it can also result from other causes).

In Knobloch’s syndrome this is usually seen in the occipital region, and aplasia is the underdevelopment of tissue again in this reference in the occipital area.

Foster–Kennedy syndrome (also known as Gowers–Paton–Kennedy syndrome, Kennedy's phenomenon or Kennedy's syndrome) refers to a constellation of findings associated with tumors of the frontal lobe.

Although "Foster–Kennedy syndrome" is equated with "Kennedy syndrome", it should not be confused with Kennedy disease, which is named for William R. Kennedy.

"Pseudo-Foster–Kennedy syndrome" is defined as one-sided optic atrophy with papilledema in the other eye but with the absence of a mass.

Noonan syndrome with multiple lentigines (NSML) which is part of a group called Ras/MAPK pathway syndromes, is a rare autosomal dominant, multisystem disease caused by a mutation in the protein tyrosine phosphatase, non-receptor type 11 gene ("PTPN11"). The disease is a complex of features, mostly involving the skin, skeletal and cardiovascular systems, which may or may not be present in all patients. The nature of how the mutation causes each of the condition's symptoms is not well known; however, research is ongoing. It is a RASopathy.

Noonan syndrome with multiple lentigines is caused by a different missense mutation of the same gene. Noonan syndrome is fairly common (1:1,000 to 1:2,500 live births), and neurofibromatosis 1 (which was once thought to be related to NSML) is also common (1:3500); however, no epidemiological data exists for NSML.

Telecanthus is often associated with many congenital disorders. Congenital disorders such as Down syndrome, fetal alcohol syndrome, Cri du Chat syndrome, Klinefelter syndrome, Turner syndrome, Ehlers-Danlos syndrome, Waardenburg syndrome often present with prominent epicanthal fold and if these folds are nasal (most commonly are) they will cause telecanthus.

Fig of the used terms

Causes of the one and a half syndrome include pontine hemorrhage, ischemia, tumors, infective mass lesions such as tuberculomas, and demyelinating conditions like multiple sclerosis.

Telecanthus (from the Greek word "tele" (τῆλε) meaning far, and the Latin word canthus, meaning either corner of the eye, where the eyelids meet) refers to increased distance between the medial canthi of the eyes, while the inter-pupillary distance is normal. This is in contrast to hypertelorism, where the inter-pupillary distance is increased.

The distance between the inner corner of the left eye and the inner corner of the right eye, is called intercanthal distance. In most people, the intercanthal distance is equal to the distance between the inner corner and the outer corner of each eye, that is, the width of the eye. The average interpupillary distance is 60–62 millimeters (mm), which corresponds to an intercanthal distance of approximately 30–31 mm. The situation, where intercanthal distance is intensely bigger than the width of the eye, is called telecanthus (tele= Greek τηλε = far, and Greek ακανθα = thorn). This can be an ethnic index or an indication for hypertelorism or hypotelorism, if it is combined with abnormal relation to the interpupillary distance (A D STEAS).

"Traumatic Telecanthus" refers to telcanthus resulting from traumatic injury to the nasal-orbital-ethmoid (NOE) complex. The diagnosis of traumatic telecanthus requires a measurement in excess of those normative values. The pathology can be either unilateral or bilateral, with the former more difficult to measure.

Cri du chat syndrome, also known as chromosome 5p deletion syndrome, 5p− syndrome (pronounced "Five P Minus") or Lejeune’s syndrome, is a rare genetic disorder due to chromosome deletion on chromosome 5. Its name is a French term ("cat-cry" or "call of the cat") referring to the characteristic cat-like cry of affected children. It was first described by Jérôme Lejeune in 1963. The condition affects an estimated 1 in 50,000 live births across all ethnicities and is more common in females by a 4:3 ratio.

The syndrome usually results from single unilateral lesion of the paramedian pontine reticular formation and the ipsilateral medial longitudinal fasciculus. An alternative anatomical cause is a lesion of the abducens nucleus (VI) on one side (resulting in a failure of abduction of the ipsilateral eye and adduction of the contralateral eye = conjugate gaze palsy towards affected side), with interruption of the ipsilateral medial longitudinal fasciculus after it has crossed the midline from its site of origin in the contralateral abducens (VI) nucleus (resulting in a failure of adduction of the ipsilateral eye).

Symptoms of entropion include:

- Redness and pain around the eye

- Sensitivity to light and wind

- Sagging skin around the eye

- Epiphora

- Decreased vision, especially if the cornea is damaged

Diprosopus often occurs in combination with other congenital disorders, particularly anencephaly, neural tube defect and cardiac malformations. When present, the brain may show abnormalities ranging from partial to complete duplication of brain structures, and/or underdevelopment of brain tissues.

People with early keratoconus typically notice a minor blurring of their vision and come to their clinician seeking corrective lenses for reading or driving. At early stages, the symptoms of keratoconus may be no different from those of any other refractive defect of the eye. As the disease progresses, vision deteriorates, sometimes rapidly. Visual acuity becomes impaired at all distances, and night vision is often poor. Some individuals have vision in one eye that is markedly worse than that in the other. The disease is often bilateral, though asymmetrical. Some develop photophobia (sensitivity to bright light), eye strain from squinting in order to read, or itching in the eye, but there is normally little or no sensation of pain. It may cause luminous objects to appear as cylindrical pipes with the same intensity at all points.

The classic symptom of keratoconus is the perception of multiple "ghost" images, known as monocular polyopia. This effect is most clearly seen with a high contrast field, such as a point of light on a dark background. Instead of seeing just one point, a person with keratoconus sees many images of the point, spread out in a chaotic pattern. This pattern does not typically change from day to day, but over time, it often takes on new forms. People also commonly notice streaking and flaring distortion around light sources. Some even notice the images moving relative to one another in time with their heart beat.

The predominant optical aberration of the eye in keratoconus is coma. The visual distortion experienced by the person comes from two sources, one being the irregular deformation of the surface of the cornea, and the other being scarring that occurs on its exposed highpoints. These factors act to form regions on the cornea that map an image to different locations on the retina. The effect can worsen in low light conditions, as the dark-adapted pupil dilates to expose more of the irregular surface of the cornea.

Heterochromia is classified primarily by onset: as either genetic or acquired.

Although a distinction is frequently made between heterochromia that affects an eye completely or only partially (segmental heterochromia), it is often classified as either genetic (due to mosaicism or congenital) or acquired, with mention as to whether the affected iris or portion of the iris is darker or lighter. Most cases of heterochromia are hereditary, caused by certain diseases and syndromes. Sometimes one eye may change color following disease or injury.