eye health

Coloboma

Generality

The coloboma is a defect in the development of the eye or eyelid. Present since birth, this congenital anomaly implies the absence of tissue in one or more ocular structures, such as cornea, iris, ciliary body, crystalline, retina, choroid and optic disk. The coloboma can manifest itself in isolation or as part of different genetic diseases and neurological syndromes.

The consequences on vision vary depending on the location and extent of the ocular malformation. For example, a coloboma limited to the iris does not cause vision problems, while a defect extended to the optic nerve or to the retina can compromise, even severely, the visual function.

Causes

The coloboma of the eye is caused by a defective closure of the choroid fissure during the early stages of prenatal development, around the 5th-7th week of gestation. This event causes a malformation in the tissue of one or more ocular structures, which can be unilateral or bilateral (that is to hit one or both eyes).

The coloboma of the eyelids can have several causes unrelated to abnormalities of the eye globe. The disease occurs due to a defective fusion of the eyelid folds, at about 7-8 weeks of gestation.

Several genetic and / or environmental factors can contribute to determining its onset.

  • Environmental factors include:
    • Alcohol (in the fetal alcohol syndrome);
    • Vitamin A deficiency;
    • Teratogenic drugs (example: thalidomide, mycophenolate mofetil, etc.);
    • Infections (toxoplasmosis, cytomegalovirus etc.).
  • Genetic factors are clearly involved where a model of Mendelian inheritance of a specific chromosomal anomaly is respected (example: mutation of the PAX2 gene, trisomy of chromosome 13, 18 or 22 etc.). In other cases, the transmission methods are less clear.

Associated conditions

The coloboma of any ocular structure can be an isolated anomaly, that is, afflict otherwise normal subjects, or occur as part of genetic syndromes that also affect other districts of the body and cause multisystem malformations. As an isolated condition, the coloboma is generally sporadic (not hereditary). Some families, however, have shown a pattern of autosomal dominant inheritance: the presence of only one copy of the abnormal gene is sufficient for the disorder to occur. If the coloboma is inherited, it is possible to find variations relative to the severity of the event among individuals, probably due to an incomplete penetrance and the variable expression of the responsible gene.

The following is a list of some multisystem syndromes associated with coloboma:

  • CHARGE syndrome: coloboma, heart defects, choanal (nasal) atresia, developmental delay, ear malformations, abnormalities of the genital or urinary tract.
  • Epidermal nevus syndrome (ENS);
  • Cat's eye syndrome (Cat-eye syndrome);
  • Veil-cardio-facial syndrome and DiGeorg syndrome;
  • Kabuki syndrome (KS).

The coloboma of the eyelids can be associated with other syndromes that cause abnormal facial development, including Treacher Collins syndrome.

Symptoms

The effects of coloboma on vision may be mild or more severe, depending on the extent and structure affected by the malformation. For example, if a coloboma affects the front of the eye, visual function may be normal, while a malformation involving the retina or optic nerve may result in a reduction in visual acuity and a defect in the visual field (central or peripheral ). Other conditions may be associated with a coloboma.

Sometimes, the eye may be small (microphthalmia) or other ocular abnormalities may be present such as: cataract (opacity of the lens of the eye), glaucoma (increased pressure inside the eye), nystagmus (eye movements involuntary), photophobia or strabismus. A coloboma of the iris may be evident due to a small missing portion, which gives the pupil an oval appearance.

A small or large developmental defect in the deeper structures of one or both eyes, on the other hand, can only be diagnosed when the ocular fundus is examined during a routine eye examination.

Chorioretinal coloboma can occur in adulthood, with loss of vision associated with retinal detachment.

Coloboma of the eyelid

The coloboma of the eyelid is a defect that varies from the lack of a small portion to the almost total absence of tissue. Most commonly, the condition affects the upper eyelid.

Treatment

Currently, there is no universal treatment for visual impairment caused by the coloboma.

Devices for correcting refractive errors can help improve visual acuity. Furthermore, the ophthalmologist can recommend special treatments to manage other problems associated with the malformation, such as cataract, the growth of new blood vessels in the back of the eye, strabismus and amblyopia (if the coloboma is unilateral).

In the case of severe microphthalmia (one or both eyeballs are abnormally small), a prosthesis can be applied to assist the symmetrical development of the face.

Other possible interventions include:

  • Coloboma of the iris: to correct the appearance of the iris, patients with coloboma can wear colored contact lenses or resort to surgical repair.
  • Chorioretinal coloboma: surgery may be necessary to treat or prevent retinal detachment.
  • Coloboma of the eyelids: the defect leaves part of the cornea uncovered. This can cause excessive dryness in the eyes due to the evaporation of tears. The eye usually needs extra lubrication and reparative surgery.