Retinoschisis is an eye disease characterized by the abnormal splitting of the retina's neurosensory layers, usually in the outer plexiform layer. Most common forms are asymptomatic, some rarer forms result in a loss of vision in the corresponding visual field.

This type of retinoschisis is very common with a prevalence of up to 7 percent in normal persons. Its cause is unknown. It can easily be confused with retinal detachment by the non-expert observer and in difficult cases even the expert may have difficulty differentiating the two. Such differentiation is important since retinal detachment almost always requires treatment while retinoschisis never itself requires treatment and leads to retinal detachment (and hence to visual loss) only occasionally. Unfortunately one still sees cases of uncomplicated retinoschisis treated by laser retinopexy or cryopexy in an attempt to stop its progression towards the macula. Such treatments are not only ineffective but unnecessarily risk complications. There is no documented case in the literature of degenerative retinoschisis itself (as opposed to the occasional situation of retinal detachment complicating retinoschisis) in which the splitting of the retina has progressed through the fovea. There is no clinical utility in differentiating between typical and reticular retinoschisis. Degenerative retinoschisis is not known to be a genetically inherited condition.

There is always vision loss in the region of the schisis as the sensory retina is separated from the ganglion layer. But like the loss is in the periphery, it goes unnoticed. It is the very rare schisis that encroaches on the macula where retinopexy is then properly used.

Many times, an optic pit is asymptomatic and is just an incidental finding on examination of the eye by a physician. However, some patients may present with the symptoms of a posterior vitreous detachment or serous retinal detachment. This is because optic pits are associated with these disorders and are even speculated to be the actual cause of these disorders when they arise in patients with optic pits (see "Associated Retinal Changes" below for a more in-depth discussion on this theory). The most common visual field defects include an enlarged blind spot and a scotoma. Visual acuity is typically not affected by the pit but may get worse if serous detachment of the macula occurs. Metamorphopsia (distorted vision) may then result.

Optic pits were first described in 1882 as dark gray depressions in the optic disc. They may, however, appear white or yellowish instead. They can also range greatly in size (e.g. some can be minuscule while others may be large enough as to occupy most of optic disc surface). Optic pits are associated with other abnormalities of the optic nerve including large optic nerve size, large inferior colobomas of the optic disc, and colobomas of the retina. The optic disc originates from the optic cup when the optic vesicle invaginates and forms an embryonic fissure (or groove). Optic pits may develop due to failure of the superior end of the embryonic fissure to close completely.

Optic pit, optic nerve pit, or optic disc pit is a congenital excavation (or regional depression) of the optic disc (also optic nerve head), resulting from a malformation during development of the eye. Optic pits are important because they are associated with posterior vitreous detachments (PVD) and even serous retinal detachments.

Vitreomacular adhesion (VMA) is a human medical condition where the vitreous gel (or simply vitreous) of the human eye adheres to the retina in an abnormally strong manner. As the eye ages, it is common for the vitreous to separate from the retina. But if this separation is not complete, i.e. there is still an adhesion, this can create pulling forces on the retina that may result in subsequent loss or distortion of vision. The adhesion in of itself is not dangerous, but the resulting pathological vitreomacular traction (VMT) can cause severe ocular damage.

The current standard of care for treating these adhesions is pars plana vitrectomy (PPV), which involves surgically removing the vitreous from the eye. A biological agent for non-invasive treatment of adhesions called ocriplasmin has been approved by the FDA on Oct 17 2012.

Traction caused by VMA is the underlying pathology of an eye disease called symptomatic VMA. There is evidence that symptomatic VMA can contribute to the development of several well-known eye disorders, such as macular hole and macular pucker, that can cause visual impairment, including blindness. It may also be associated with age-related macular degeneration (AMD), diabetic macular edema (DME), retinal vein occlusion, and diabetic retinopathy (DR).

An ectopic cilia is a special type of distichia. It is usually found in younger dogs. Commonly affected breeds include Poodles, Golden Retrievers, and Shih Tzus. The eyelash exits through the conjunctiva of the eyelid facing toward the eye, usually at the middle of the upper eyelid. It can cause intense pain and corneal ulcers. Treatment is surgery or cryotherapy.

Individuals with Stickler syndrome experience a range of signs and symptoms. Some people have no signs and symptoms; others have some or all of the features described below. In addition, each feature of this syndrome may vary from subtle to severe.

A characteristic feature of Stickler syndrome is a somewhat flattened facial appearance. This is caused by underdeveloped bones in the middle of the face, including the cheekbones and the bridge of the nose. A particular group of physical features, called the Pierre Robin sequence, is common in children with Stickler syndrome. Robin sequence includes a U-shaped or sometimes V-shaped cleft palate (an opening in the roof of the mouth) with a tongue that is too large for the space formed by the small lower jaw. Children with a cleft palate are also prone to ear infections and occasionally swallowing difficulties.

Many people with Stickler syndrome are very nearsighted (described as having high myopia) because of the shape of the eye. People with eye involvement are prone to increased pressure within the eye (ocular hypertension) which could lead to glaucoma and tearing or detachment of the light-sensitive retina of the eye (retinal detachment). Cataract may also present as an ocular complication associated with Stickler's Syndrome. The jelly-like substance within the eye (the vitreous humour) has a distinctive appearance in the types of Stickler syndrome associated with the COL2A1 and COL11A1 genes. As a result, regular appointments to a specialist ophthalmologist are advised. The type of Stickler syndrome associated with the COL11A2 gene does not affect the eye.

People with this syndrome have problems that affect things other than the eyes and ears. Arthritis, abnormality to ends of long bones, vertebrae abnormality, curvature of the spine, scoliosis, joint pain, and double jointedness are all problems that can occur in the bones and joints. Physical characteristics of people with Stickler can include flat cheeks, flat nasal bridge, small upper jaw, pronounced upper lip groove, small lower jaw, and palate abnormalities, these tend to lessen with age and normal growth and palate abnormalities can be treated with routine surgery.

Another sign of Stickler syndrome is mild to severe hearing loss that, for some people, may be progressive (see hearing loss with craniofacial syndromes). The joints of affected children and young adults may be very flexible (hypermobile). Arthritis often appears at an early age and worsens as a person gets older. Learning difficulties, not intelligence, can also occur because of hearing and sight impairments if the school is not informed and the student is not assisted within the learning environment.

Stickler syndrome is thought to be associated with an increased incidence of mitral valve prolapse of the heart, although no definitive research supports this.

A distichia is an eyelash that arises from an abnormal spot on the eyelid. This abnormality, attributed to a genetic mutation, is known to affect dogs and humans. Distichiae (the abnormal eyelash) usually exit from the duct of the meibomian gland at the eyelid margin. They are usually multiple and sometimes more than one arises from a duct. They can affect either the upper or lower eyelid and are usually bilateral. The lower eyelids of dogs usually have no eyelashes.

Distichiae usually cause no symptoms because the lashes are soft, but they can irritate the eye and cause tearing, squinting, inflammation, and corneal ulcers and scarring. Treatment options include manual removal, electrolysis, electrocautery, cryotherapy, and surgery.

Cystoid macular edema (CME) involves fluid accumulation in the outer plexiform layer secondary to abnormal perifoveal retinal capillary permeability. The edema is termed "cystoid" as it appears cystic; however, lacking an epithelial coating, it is not truly cystic. The cause for CME can be remembered with the mnemonic "DEPRIVEN" (diabetes, epinepherine, pars planitis, retinitis pigmentosa, Irvine-Gass syndrome, venous occlusion, E2-prostaglandin analogues, nicotinic acid/niacin).

Diabetic macular edema (DME) is similarly caused by leaking macular capillaries. DME is the most common cause of visual loss in both proliferative, and non-proliferative diabetic retinopathy.

Macular edema occurs when fluid and protein deposits collect on or under the macula of the eye (a yellow central area of the retina) and causes it to thicken and swell (edema). The swelling may distort a person's central vision, because the macula holds tightly packed cones that provide sharp, clear, central vision to enable a person to see detail, form, and color that is directly in the centre of the field of view.

The most obvious symptom of macropsia is the presence of exceptionally enlarged objects throughout the visual field. For example, a young girl might see her sister’s books as the same size as her sister. Stemming from this symptom, someone with macropsia may feel undersized in relation to his or her surrounding environment. Patients with macropsia have also noted the cessation of auditory function prior to the onset of visual hallucination, indicating possible seizure either before or after the hallucination. A buzzing sound in the ears has also been reported immediately before macropsia development. Some patients claim that symptoms may be eased if an attempt is made to physically touch the object which appears enormous in size. It is important to note, however, that patients typically remain lucid and alert throughout episodes, being able to recount specific details. A person with macropsia may have no psychiatric conditions. Symptoms caused chemically by drugs such as cannabis, magic mushrooms, or cocaine tend to dissipate after the chemical compound has been excreted from the body. Those who acquire macropsia as a symptom of a virus usually experience complete recovery and restoration of normal vision.

Dysmetropsia in one eye, a case of aniseikonia, can present with symptoms such as headaches, asthenopia, reading difficulties, depth perception problems, or double vision. The visual distortion can cause uncorrelated images to stimulate corresponding retinal regions simultaneously impairing fusion of the images. Without suppression of one of the images symptoms from mild poor stereopsis, binocular diplopia and intolerable rivalry can occur.

In addition to small palpebral fissures, features include epicanthus inversus (fold curving in the mediolateral direction, inferior to the inner canthus), low nasal bridge, ptosis of the eyelids and telecanthus.

Stickler syndrome (hereditary progressive arthro-ophthalmopathy) is a group of genetic disorders affecting connective tissue, specifically collagen. Stickler syndrome is a subtype of collagenopathy, types II and XI. Stickler syndrome is characterized by distinctive facial abnormalities, ocular problems, hearing loss, and joint problems. It was first studied and characterized by Gunnar B. Stickler in 1965.

Blepharophimosis syndrome is an autosomal dominant characterized by blepharophimosis (horizontal shortening of the palpebral fissures), ptosis (upper eyelid drooping, usually with the characteristics of congenital ptosis), epicanthus inversus (skin folds by the nasal bridge, more prominent lower than upper lid), and telecanthus (widening of the distance between the medial orbital walls). This syndrome is caused by mutations in the FOXL2 gene, either with premature ovarian failure (BPES type I) or without (BPES type II). It may also be associated with lop ears, ectropion, hypoplasia of superior orbital rims, and hypertelorism.

The joint changes include hyperextensibility (double-jointedness) and arthritis. Babies and young children with Stickler syndrome usually have very hyperextensible joints. As an affected child gets older, they may experience pain and stiffness from overuse of a joint. Osteoarthritis of the large joints often develops during the third or fourth decade. The joint changes in Marshall syndrome are of the same type but to a lesser degree. There also may be changes in the bones that show up on X-ray but generally are not a problem.

Myopia is the most common eye problem in Marshall syndrome. Cataracts also occur more frequently and detached retina less frequently than in Stickler syndrome. Myopia also is the most common problem with the eyes in Stickler syndrome. In the latter syndrome, extreme myopia may lead to severe eye problems such as detached retina more frequently than in Marshall syndrome.

There are a broad range of psychological and emotional effects that a person suffering macropsia may experience. One competing theory has radically stated that macropsia may be an entirely psychological pathological phenomenon without any structural defect or definite cause. He or she may be in an irritable or angry state, or in contrast, a euphoric state. There is evidence that those who experience Alice in Wonderland Syndrome and associated macropsia are able to recount their experiences with thorough detail. There may be no evidence of psychiatric disturbance and, as a result, no psychiatric therapy may be required. Psychological conditions often arise from macropsia, but the general consensus is that they do not cause macropsia. Those afflicted may experience extreme anxiety both during and after episodes as a result of the overwhelming nature of his or her distorted visual field. Due to the fear and anxiety associated with the condition, those who have previously suffered an episode hesitate to recount the episode, although retain the ability to do so. Psychologically, a person with macropsia may feel separation and dissociation from the outside world and even from immediate family. This feeling of dissociation has mostly been noted in child or adolescent patients. The patient may feel that he or she must unfairly contend with hostile and aggressive forces due to the gigantic nature of the surrounding environment. The defense against said forces is usually expressed verbally. The patient may falsely present an outgoing or flamboyant persona, while remaining fearful of people internally. He or she, in an attempt to balance the size distortion, may try to make others feel small in size through insult or hostile behavior. The psychological impact of macropsia on long time sufferers who have had the condition since childhood may be greater and lead to severe ego-deficiencies. An alternate interpretation of the condition is that macropsia is a response to biophysiological contraction and has no psychological roots. Thus, when a patient reaches for an enlarged object, he or she is overcoming that physiological contraction . However, this theory has been under much scrutiny.

The primary characteristics of FTHS are brachycephaly (flat head), wide fontanelle (soft spot on a baby’s head), prominent forehead, hypertelorism (abnormally wide distance between the eyes), prominent eyes, macrocornea (large corneas), optic disc edema, full cheeks, small chin, bowing of the long bones in the arms or legs, and finger deformities. Protruding, simple ears and a prominent coccyx (tailbone) are also regarded as important diagnostic signs of FTHS.

The following signs are associated with the disease

- Abnormal heart development

- Abnormal skeletal development

- Hypermobile joints

- Large fingers

- Knock-knees

- Widely spaced teeth

- Bell-shaped chest (flared ribs)

- Compression of spinal cord

- Enlarged heart

- Dwarfism

- Heart murmur

- below average height for certain age

Patients with Morquio syndrome appear healthy at birth. They often present with spinal deformity, and there is growth retardation and possibly genu valgum in the second or third year of life. A patient with Morquio's syndrome is likely to die at an early age. Symptoms of the disease may include:

- Short stature and short neck (caused by flat vertebrae)

- Moderate kyphosis or scoliosis

- Mild pectus carinatum ("pigeon chest")

- Cervical spine: odontoid hypoplasia, atlanto-axial instability; may be associated with myelopathy with gradual loss of walking ability

- Joint laxity, mild dysostosis multiplex, dysplastic hips, large unstable knees, large elbows and wrists, and flat feet

- The combined abnormalities usually result in a duck-waddling gait

- Mid-face hypoplasia and mandibular protrusion

- Thin tooth enamel

- Corneal clouding

- Mild hepatosplenomegaly

Regarding the life span of people with Morquio, some can die as early as 2 or 3 years old, and some can live up to 60 or 70 years old. The oldest known person with Morquio syndrome type IV A was Kenneth D. Martin, who was born in Osage City, Kansas, USA and was 81 years old at the time of his death

Closed-eye hallucinations and closed-eye visualizations (CEV) are a distinct class of hallucination. These types of hallucinations generally only occur when one's eyes are closed or when one is in a darkened room. They can be a form of phosphene. Some people report closed-eye hallucinations under the influence of psychedelics. These are reportedly of a different nature than the "open-eye" hallucinations of the same compounds.

Antley–Bixler syndrome presents itself at birth or prenatally. Features of the disorder include brachycephaly (flat forehead), craniosynostosis (complete skull-joint closure) of both coronal and lambdoid sutures, facial hypoplasia (underdevelopment); bowed ulna (forearm bone) and femur (thigh bone), synostosis of the radius (forearm bone), humerus (upper arm bone), and trapezoid (hand bone); camptodactyly (fused interphalangeal joints in the fingers), thin ilial wings (outer pelvic plate), and renal malformations.

Other symptoms, such as cardiac malformations, proptotic exophthalmos (bulging eyes), arachnodactyly (spider-like fingers), as well as nasal, anal, and vaginal atresia (occlusion) have been reported.

Facial features found in this syndrome include

- dolichocephaly

- hypertelorism

- ptosis

- microretrognathia

- high arched palate

- long flat philtrum

- low set ears

Non facial features of this syndrome include

- hyperextensibility

- hypotonia

- lateral meningoceles

The lateral meningocoles are a common finding in this syndrome. They may be associated with neurological abnormalities and result in bladder dysfunction and neuropathy.

Morquio syndrome (referred to as mucopolysaccharidosis IV, MPS IV, Morquio-Brailsford syndrome, or Morquio) is a rare metabolic disorder in which the body cannot process certain types of mucopolysaccharides. This birth defect, which is autosomal recessive, is thus a lysosomal storage disorder that is usually inherited. In the US, the incidence rate for Morquio is estimated at between 1 in 200,000 and 1 in 300,000 live births.

The build-up or elimination of mucopolysaccharides, rather than processing by their usual biochemical pathways, causes various symptoms. These involve accumulation of keratan sulfate.

Antley–Bixler syndrome, also called trapezoidocephaly-synostosis syndrome, is a rare, very severe autosomal recessive congenital disorder characterized by malformations and deformities affecting the majority of the skeleton and other areas of the body.