Coloboma

What is a Coloboma?

Ocular coloboma is an eye condition that’s present at birth. A coloboma is a missing piece of tissue in one of the structures that make up the eye.

A coloboma can appear in one or both eyes. When colobomas occur in both eyes, they may affect each one differently or in the same way. 

Colobomas can contribute to vision loss or light sensitivity problems. Coloboma of the iris, the most common type, doesn’t usually result in vision loss.  

How Common is Coloboma?

Coloboma develops in approximately 1 in 10,000 babies every year. Because some cases of coloboma don’t trigger any symptoms, the actual number may differ. People can have undiagnosed coloboma and never experience symptoms or complications.

Types of Coloboma

Ocular colobomas can affect different parts of the eye. The types of coloboma include:

Lens Coloboma

The lens is a clear disc that helps your eye focus. It’s located inside your eye, behind the iris (colored part).

A lens coloboma happens when part of the lens is missing. When this occurs, the lens can lose its normal shape. An irregularly shaped lens can cause vision problems, such as a refractive error or amblyopia (lazy eye). 

Macular Coloboma

The center of the retina is called the macula. This eye structure provides central vision and allows you to see fine details.

A macular coloboma occurs when the macula doesn't develop normally. This type can have a significant impact on vision.

Eyelid Coloboma

An eyelid coloboma appears as a missing piece of the upper or lower eyelid.

Most cases of eyelid coloboma affect the upper lid. They usually look like a notch in the eyelid. Severe cases of this condition can cause the visible part of the eyelid to be completely missing.

Uveal Coloboma 

The wall of the eye is composed of the uvea, a middle layer that includes:

• Iris (colored part of the eye)
• Choroid
• Ciliary body 

There are two different types of uveal coloboma:

Iris Coloboma

An iris coloboma can cause a “keyhole” or “cat-eye” appearance. Because part of the iris is missing, it looks like the pupil extends into the colored area of the eye.

Iris coloboma can cause the pupil to let too much light into the eye. This may lead to light sensitivity. People with iris coloboma might squint in bright light.

Chorioretinal Coloboma

Chorioretinal coloboma is a uveal coloboma in the retina. This means part of the retina is missing. The retina lines the back wall inside your eye. It senses light and relays signals to your brain so you can see.

Chorioretinal coloboma typically doesn’t cause vision problems. But in rare cases, it can cause retinal detachment. This happens when the retina pulls away from the back of the eye.

Optic Nerve Coloboma

The optic nerve is an essential structure in the eye. It helps relay visual information to the brain. Optic nerve coloboma occurs when this nerve doesn’t develop completely.

This type of coloboma can cause blurry vision or blind spots.

What Causes Coloboma?

Ocular coloboma occurs because of abnormal eye development before a baby’s born. The term coloboma stems from the Greek word meaning “curtailed.”

A baby's eyes develop rapidly in the first three months of gestation. During this time, a gap (choroidal fissure) develops at the base of the stalks that grow into the eye.

In most cases, this fissure closes before the seventh week of gestation. When it doesn’t close, a coloboma forms.

The exact cause of ocular coloboma can vary. They include:

Genetic Factors

Genetics can be a leading factor in why some fetuses have coloboma. Studies have shown that certain genes in the parents may increase the chances of a child having a coloboma. However, there’s insufficient research to determine which genes cause this condition.

Coloboma can sometimes result from a genetic disorder, such as cat-eye syndrome. In this example, the rare disorder takes its name from the unique shape found with an iris coloboma caused by a genetic mutation. 

It’s important to note that a family history of coloboma or a specific syndrome isn’t always present in babies born with a coloboma. This means that the condition can appear by chance.

Environmental Factors

Certain environmental factors, such as alcohol use during early pregnancy, can increase the risk of coloboma. When this occurs, affected babies usually have other health problems as well.

Other Health Conditions

Coloboma can occur with health conditions that affect other parts of the body, such as:

CHARGE Syndrome

CHARGE syndrome is present at birth and can affect many parts of the body. CHARGE is an acronym that stands for:

• Coloboma
• Heart defect
• Atresia choanae
• Restricted growth and development
• Genital abnormality
• Ear abnormality

CHARGE symptoms vary from person to person and range from mild to severe. Some people have many symptoms, and others only have a few.

Wolf-Hirschhorn Syndrome

Wolf-Hirschhorn syndrome (WHS) is a rare genetic disorder. Symptoms can affect many parts of the body. In addition to coloboma, WHS symptoms include:

• Delayed growth and development
• Intellectual disability
• Low muscle tone
• Seizures

Symptoms of a Coloboma

The symptoms of a coloboma vary depending on the type. Some people don’t have any symptoms. Others may experience vision problems, such as:

• Increased light sensitivity 
• Poor vision
• Vision loss or blindness
• Blind spots or vision impairment in a specific area of the field of vision

Some types, such as iris coloboma, cause a visible anomaly in the iris. Other types, like eyelid coloboma, can cause excessive dryness in the eye. 

Eye Problems Associated With Coloboma

Ocular coloboma can increase your child’s chances of developing eye conditions later in life, such as:

• Cataracts 
• Glaucoma 
• Refractive errors
• Retinal detachment
• Growth of new blood vessels in the back of the eye

Your ophthalmologist will monitor your child’s eyes as they grow, managing any changes that occur.

Diseases Associated With Coloboma of the Eye 

In some cases, a coloboma develops because of specific diseases or chromosomal abnormalities that involve other body structures. 

Diseases and syndromes that are associated with coloboma include:

• Goldenhar syndrome. This rare congenital condition is characterized by irregular development of the eye, ear, and spine.
• Duane syndrome.  This condition is a congenital and non-progressive type of strabismus caused by abnormal development of the sixth cranial nerve.
• Treacher Collins syndrome. This is a genetic disorder that results in deformities of the eyes, eyes, cheekbones, and chin. Disease severity will vary. 
• CHARGE syndrome. People with this condition experience heart defects, choanal atresia, developmental delays, genital or urinary tract anomalies, or ear malformations 
• Kabuki syndrome. A rare multisystem disorder, kabuki syndrome causes different abnormalities like distinctive facial features, delayed growth, intellectual disability, skeletal problems, and short stature.
• 13q deletion syndrome. This rare genetic disease appears when some or all of the long arm of human chromosome 13 is deleted. People born with this condition have low birth weight, head and facial malformations, abnormalities of the eyes, and much more. 
• Wolf-Hirschhorn syndrome. This genetic disorder can cause a distinctive facial appearance, delayed growth and development, intellectual disability, low muscle tone, and seizures.
• Microphthalmia. One or both eyes are atypically small. In some cases, the eyeball may seem to be missing entirely. 

Diagnosing a Coloboma

To diagnose a coloboma, an ophthalmologist will perform a comprehensive eye exam using an ophthalmoscope. This instrument allows your doctor to examine the inside of your baby’s eyes.

When your child is old enough to communicate, a visual acuity test can assess their vision.

Treatment Options for a Coloboma 

There is no cure for coloboma, and treatment won’t replace the missing tissue in the eyes. However, several treatments can improve your child’s vision and relieve symptoms.

Glasses or Contacts

People with refractive errors due to coloboma can wear eyeglasses or contact lenses to see more clearly.

People with iris colobomas might opt to wear colored contacts that make their pupils appear rounder.

Low Vision Aids

Some patients with coloboma experience vision loss that can’t be corrected with glasses or contacts. In these cases, low-vision devices can help. These include magnifiers and other forms of assistive technology.

Eye Patch or Eye Drops

Children with coloboma in one eye may benefit from wearing an eye patch or eye drops. These treatments help prevent amblyopia (lazy eye).

Surgery 

Various surgical procedures can treat different types of coloboma. For example, surgery can correct eyelid coloboma and iris coloboma.