Generality
Coloboma is a developmental defect 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, lens, retina, choroid and disc. optical. Coloboma can occur in isolation or as part of different genetic diseases and neurological syndromes.
Causes
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 (i.e. striking one or both eyes).
Coloboma of the eyelids can have several causes unrelated to abnormalities of the globe of the eye. The disease arises from a defective fusion of the eyelid folds, at approximately 7-8 weeks of gestation.
Several genetic and / or environmental factors can contribute to determining its onset.
- Environmental factors include:
- Alcohol (in fetal alcohol syndrome);
- Vitamin A deficiency;
- Teratogenic drugs (example: thalidomide, mycophenolate mofetil etc.);
- Infections (toxoplasmosis, cytomegalovirus, etc.).
- Genetic factors are clearly involved where a Mendelian inheritance model of a specific chromosomal anomaly is respected (example: PAX2 gene mutation, trisomy of chromosome 13, 18 or 22 etc.). In other cases, the methods of transmission are less clear.
Associated conditions
Coloboma of any ocular structure can be an "isolated anomaly, affecting otherwise normal subjects, or occur as part of genetic syndromes that also affect other parts of the body and cause multisystem malformations. As an isolated condition, coloboma is generally sporadic (not hereditary). Some families, however, have shown an autosomal dominant pattern of inheritance: the presence of only one copy of the abnormal gene is sufficient for the disorder to occur. If the coloboma is inherited, there may be variations in the severity of the manifestation between individuals, probably due to incomplete penetrance and the variable expressivity of the responsible gene.
Below is a list of some multisystemic syndromes associated with coloboma:
- CHARGE syndrome: coloboma, heart defects, choanal (nasal) atresia, developmental delay, ear malformations, genital or urinary tract abnormalities.
- Epidermal nevus syndrome (ENS);
- Cat-eye syndrome (Cat-eye syndrome);
- Velo-cardio-facial syndrome and DiGeorg syndrome;
- Kabuki Syndrome (KS).
Coloboma of the eyelids can be associated with other syndromes that result in abnormal facial development, including Treacher Collins syndrome.
Symptoms
The effects of coloboma on vision can 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 which involving the retina or the optic nerve can lead to 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 in size (microphthalmia) or other ocular abnormalities may be present such as: cataract (clouding 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 an oval appearance to the pupil.
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 fundus is examined during a routine eye exam.
Chorioretinal coloboma can present in adulthood, with vision loss 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 coloboma.
Devices to correct refractive errors can help improve visual acuity. In addition, the ophthalmologist can recommend special treatments to manage other problems associated with the malformation, such as cataracts, the growth of new blood vessels in the back of the eye. , strabismus and amblyopia (if the coloboma is unilateral).
In case of severe microphthalmia (one or both eyeballs are abnormally small), a prosthesis can be applied to assist in the symmetrical development of the face.
Other possible interventions include:
- Coloboma of the iris: To correct the appearance of the iris, patients with coloboma may wear colored contact lenses or seek surgical repair.
- Chorioretinal coloboma: Surgery may be needed to treat or prevent retinal detachment.
- Coloboma of the eyelids: the defect leaves part of the cornea uncovered. This can induce excessive dryness due to evaporation of tears. The eye usually needs additional lubrication and repair surgery.
