It is defined as a congenital disability in any ocular tissue.
This defect typically presents as absent tissue or space in a site compatible with aberrant closure of the optic fissure.
A coloboma (from the Greek coloboma, which means defect) is a hole in one of the eye’s structures, such as the iris, retina, choroid, or optic disc.
Coloboma is an eye abnormality that occurs before birth. Colobomas are missing pieces of tissue in the structures that make up the eye. Most cases of coloboma affect only the iris.
Colobomas involving the iris, which result in a “keyhole” appearance of the pupil, generally do not lead to loss of vision.
Causes of a coloboma
Coloboma arises from the abnormal development of the eye. The hole is present from birth (except in one case, it developed during the first months of the child’s life).
And it can be caused during the second month of development before birth, a vein/gap called an optic fissure (also known as a choroidal fissure or embryonic fissure, choroidal fissure).
This vein/gap, present during the early stages of prenatal development, does not close completely to form the eye’s structures before a child is born.
When the optic fissure does not close completely, the result is a coloboma. The location of the coloboma depends on the part of the optic fissure that did not close. The condition can also result from a chromosomal abnormality that affects one or more genes.
The risk of coloboma can also be increased by environmental factors that affect early development, such as exposure to alcohol during pregnancy. In these cases, the affected people usually have other health problems in addition to coloboma.
People with coloboma may also have other eye abnormalities, such as:
- It is clouding of the lens (cataracts).
- Increased pressure inside the eye (glaucoma) can damage the optic nerve, vision problems such as myopia, involuntary back and forward eye movements (nystagmus), or separation of the retina from the back of the eye (retinal detachment).
When coloboma occurs on its own, it is described as nonsyndromic or isolated. Colobomas that affect the eyeball must be distinguished from spaces in the eyelids.
While these eyelid gaps are also called colobomas, they arise from abnormalities in different structures during early development.
Coloboma can be associated with a mutation in the PAX2 gene.
Eye abnormalities have been shown to occur in more than 90% of children with fetal alcohol syndrome.
Other eye malformations including or related to coloboma:
CHARGE syndrome is a term that came into use as an acronym for the set of unusual congenital features seen in a series of newborn infants.
The letters represent coloboma of the eye, heart defects, nasal choanal atresia, delayed growth and development, genital and urinary abnormalities, ear abnormalities, and deafness. Although these characteristics are no longer used to make a diagnosis, the name has been retained.
Cat-eye syndrome is caused by the short arm (p) and a small section of the long arm (q) of human chromosome 22 that is present three (trisomic) or four times (tetrasomic) instead of the usual two times.
The term “cat’s eye” was coined due to the unique appearance of vertical colobomas in the eyes of some patients.
Patau syndrome (trisomy 13) is a chromosomal abnormality that can cause several deformities, some of which include structural defects of the eyes, including:
- Microphthalmia, Peters anomaly, cataract, fundus iris and coloboma, retinal dysplasia or retinal detachment, sensory nystagmus, cortical visual loss, and optic nerve hypoplasia.
- Treacher Collins syndrome is an autosomal dominant syndrome caused by the TCOF1 mutation.
Coloboma is part of a set of characteristic facies that present craniofacial malformations, such as low-slant eyes, abnormalities of the ear, or zygomatic bone and jaw hypoplasia (micrognathia).
Tilted Disc Syndrome: A rare congenital malformation associated with myopic astigmatism causes the optic disc to enter the retina improperly, also known as Fuchs’ coloboma.
Most often, isolated coloboma is not inherited, and there is only one affected individual in a family. However, the affected person still risks transmitting coloboma to their children.
Coloboma can have different inheritance patterns in cases where it runs in families.
Less commonly, the isolated coloboma may have X-dominant or X-linked recessive, recessive inheritance patterns. X-linked means that a gene associated with this condition is located on the X chromosome, one of the two sex chromosomes.
In men (who have only one X chromosome), a mutation in the only copy of a gene in each cell causes the disorder. In most cases, men experience more severe disease symptoms than women.
Men are more affected by recessive X-linked disorders because women are unlikely to have two altered copies of a particular gene.
Description of a coloboma
The classic description in the medical literature is of a keyhole-shaped defect. In this presentation, the student is referred to as a “keyhole.” A coloboma can occur in one eye (unilateral) or both eyes (bilateral).
They can appear as notches or gaps in one of several parts of the eye, including:
The colored part of the eye is called the iris; the retina, the specialized light-sensitive tissue that lines the back of the eye; the layer of blood vessels under the retina called the choroid; or the optic nerves, which carry information from the eyes to the brain.
The level of visible impairment in people with a coloboma can range from having no vision problems to seeing only light or dark, depending on the severity and position of the coloboma (or more than one colobomata is present).
Colobomas that affect the retina cause vision loss in specific parts of the visual field, usually in the upper part.
Large retinal colobomas or those that affect the optic nerve can cause low vision, which means vision loss that cannot be completely corrected with glasses or contact lenses.
Some people with coloboma also have a condition called microphthalmia. In this condition, one or both eyeballs are abnormally small.
In some affected people, the eyeball may appear wholly lost; however, the remaining ocular tissue is usually present even in these cases.
However, the terms anophthalmia and severe microphthalmia are often used interchangeably. Microphthalmia may or may not cause significant vision loss.
Signs and symptoms
The effects of a coloboma on vision can be mild or more severe depending on the size and location of the space.
If, for example, only a tiny part of the iris is missing, vision may be expected, while 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.
It is more likely to cause problems with mobility if the lower visual field is absent. Other conditions may be associated with coloboma.
Sometimes the eye can be reduced in size; a condition called microphthalmia. Glaucoma, nystagmus, scotoma, or strabismus may also appear. There may be some increase in sensitivity to light due to a larger pupil.
Diagnosis of coloboma
A coloboma is usually oval or kite-shaped with a rounded end toward the center. There may be some vessels (retinal or choroidal) at the edges. The surface may have irregular depression.
Iris coloboma can be treated in several ways. A simple cosmetic solution is a specialized cosmetic contact lens with an artificial pupil aperture. Surgical repair of the iris defect is also possible.
Surgeons can close the defect by sewing in some cases. Specialist surgeons have successfully used artificial iris prosthetic devices, such as the Human Optics artificial iris.
This device cannot be used if the natural lens is in place and is not suitable for children. Suture repair is a better option where the lens is still present.
Vision can be improved with glasses, contact lenses, or even laser eye surgery, but it can be limited if the retina is affected or amblyopia.
Epidemiology and incidences of a coloboma
Coloboma is a congenital ocular disability that results from abnormal eye development during embryogenesis. The number of cases is 0.5 to 0.7 per 10,000 births, making it a rare condition.
Because coloboma doesn’t always affect vision or the external appearance of the eye, some people with this condition probably go undiagnosed.
Notable people with coloboma include the late actor John Ritter, New York Times columnist Andrew Ross Sorkin, tennis player Arnaud Clément, alternative rock singer Lachi, George Soros, and Madeleine McCann.
McCann, a British girl, disappeared from her parents’ rented apartment in May 2007, just before her fourth birthday.
Posters and online campaigns promoting Madeleine’s search use the word “Search” with the first “O” in the word drawn in the shape of a coloboma radius extending from the pupil at the 7 o’clock position. O’clock.
What is an eyelid coloboma?
It is a defect that varies from a small notch to an almost total absence of the eyelid. The most common is that it affects the upper eyelid.
What other abnormalities occur with an eyelid coloboma?
Eyelid coloboma can be associated with Goldenhar syndrome, characterized by growth in the eye (limbal dermoid), abnormal eye movement (Duane syndrome), ear abnormalities, or vertebral abnormalities.
Another syndrome associated with coloboma of the lower eyelid is Treacher Collins syndrome, characterized by depression of the cheeks, a sloping appearance of the eye, and a small jaw.
How is an eyelid coloboma treated?
The eye generally requires additional lubrication to prevent drying of the surface and may eventually require surgery to close the defect.