What is coloboma?
Coloboma (pronounced "kah-luh-BOW-muh") is a condition characterized by missing tissues in and around the eye. This results in gaps or notches in part of the eye’s structure. Coloboma is a congenital condition, meaning it is present at birth. It is caused by abnormal development during gestation.
A coloboma may be present in one eye (unilateral) or both eyes (bilateral). In cases of bilateral coloboma, each eye can be affected differently.
The condition can be inherited or happen spontaneously. The most likely cause is a genetic disorder affecting the development of the eye before birth.
While some people with coloboma have no symptoms, many experience blurry or reduced vision and light sensitivity. Vision loss and blindness are also possible in severe cases.
Types of coloboma
Colobomas occur due to incomplete growth or development of some structures of the eye and the eyelids. They can affect the:
- Eyelids – The outer layers of skin that protect the eye
- Iris – The colored part of the eye
- Retina – The light-sensitive tissue at the back of the eye
- Optic nerve – The nerve at the back of the eye that transmits visual information to the brain
- Natural crystalline lens – A structure that helps vision focus at different distances
It is common for multiple coloboma types to be present together. For example, a child may have both eyelid coloboma and retinal coloboma.
Iris coloboma
Iris coloboma often looks like a black notch on the pupil due to missing tissue. In partial coloboma, this may cause the pupil to look more oval-shaped than round.
With complete iris coloboma, the notch extends to the edge of the iris, giving the pupil a keyhole or cat-like appearance. Iris coloboma appears in another genetic condition called cat eye syndrome, named specifically for the rare feature.
The iris coloboma can create a defect or hole in the iris that is not connected or attached to the pupil. This may result in the appearance of a second pupil in some cases. In these instances, the coloboma works as a second pupil and a second visual input is focused on the retina. This can cause blurry or double vision.
When the coloboma is attached to the pupil, minor vision issues, such as light sensitivity, can occur. Colored (prosthetic) contact lenses may be prescribed to relieve issues with light sensitivity. They can also give the pupils a rounder, more natural appearance.
Lens coloboma
Lens coloboma is characterized by missing tissue in the natural lens of the eye. This can cause blurry vision.
Cataracts are also common with lens coloboma. This occurs when the naturally clear lens begins to cloud. Cataracts can make colors appear dull and vision seem hazy or blurred. Glare and halos around lights are also common, making driving at night difficult.
Retina coloboma
Retinal coloboma, also called chorioretinal coloboma, happens when a gap occurs at the back of the eye. This area contains light-sensitive retinal tissue and the choroid (a tissue with many blood vessels right behind the retinal layer). Coloboma in this region leads to missing retinal tissue and blood vessels.
While the retina is vital for clear vision, people with retinal coloboma may show no symptoms. However, some complications can arise from the condition, including:
- Loss of visual clarity
- Blind spots, especially in the central and upper regions of the visual field
- Retinal tear or retinal detachment (can happen at any age)
- Distorted vision
- Abnormal blood vessel growth near the coloboma
- Cataracts
Retinal coloboma may affect one or both eyes. It is not typically diagnosed at birth, as the retina is an internal structure that cannot be seen from outside.
Treatment for retinal coloboma may not be necessary if the patient experiences no symptoms or complications. However, surgical treatment may be needed for retinal detachment, cataracts and abnormal blood vessel growth.
Optic nerve coloboma
Optic nerve coloboma, also known as optic disc coloboma, occurs when there is tissue missing in the optic nerve. The optic nerve takes images created by the eye and sends them to the brain, making it essential for clear vision.
Depending on the size and location of the affected area, optic nerve coloboma may or may not impact vision. Many people with this condition experience blurry or reduced vision and blind spots.
Like retinal coloboma, optic nerve coloboma is not usually detected without an eye exam. Although there is no cure, low vision aids can help those whose eyesight has been affected by the condition.
Eyelid coloboma
Eyelid coloboma refers to missing or incomplete eyelid tissue, which occurs when the skin folds of the eyelid fail to fuse. The results can be minor, with the eyelid appearing uneven or the edges looking incomplete. In more severe cases, half the upper eyelid may be missing.
Eyelid coloboma may affect one or both eyes. It may involve anywhere from one eyelid to both eyelids of each eye.
Treatments are designed to protect the eye and keep it moist — a task typically performed by the eyelids. Options typically include:
- Patches
- Scleral contact lenses
- Moisture chamber eye bandages
- Artificial tears
- Ointments
Severe cases of eyelid coloboma may require surgical treatment to create or complete an eyelid.
Because the eyelids work to protect and keep the eyes hydrated, missing part or all of the eyelid can cause dry eye. Having chronic dry eyes can lead to additional complications, such as:
- Cornea inflammation (keratitis)
- Corneal ulcers
- Corneal scarring
Eyelid coloboma is a rare condition, affecting one in every 10,000 births. Gender and race have little to no impact on risk.
What causes coloboma?
Eye colobomas occur when certain structures fail to fuse during fetal development.
During gestation, a seam known as a choroidal fissure (also called the optic fissure or embryonic fissure) connects and secures to form the structure of the eye. Typically, this connection occurs between week five and week seven of pregnancy.
If the choroidal fissure fails to close by the end of week seven, a gap or coloboma is left. The location of these gaps in the fissure determines where the colobomas are located.
Genetic defects or chromosomal abnormalities are the most likely cause of incomplete optic fissure fusion. These abnormalities can be inherited or happen spontaneously.
Coloboma of the eye may occur with other genetic abnormalities if caused by a genetic disorder. Some genetic conditions in which coloboma is found include:
- CHARGE syndrome
- Walker-Warburg syndrome
- MIDAS syndrome
- Cat eye syndrome
- Aicardi syndrome
Environmental conditions and maternal health also play a part in the development of eye coloboma. Research suggests that consuming alcohol during pregnancy can increase the risk of a baby being born with coloboma.
Signs of coloboma
If a child has coloboma on a structure that is visible from the outside, like the eyelid or iris, the signs will be somewhat clear. However, coloboma that affects an internal structure will require a dilated eye exam to diagnose. Below are some of the most common signs of eye coloboma:
Strange pupil shape
As mentioned earlier, having an irregular pupil shape is a telltale sign of iris coloboma. In minor cases, the pupil may look more like an oval than a perfect circle.
More severe instances could make the pupil look like it extends to the bottom of the iris. This can make the pupils look cat-like or keyhole-shaped.
One or more incomplete eyelids
Eyelid coloboma will affect the appearance and function of one or more eyelids. A notch or dip in the eyelid is possible, or the edges of the eyelid can appear droopy as if melted. In severe cases, the eyelid may be missing completely.
Usually, the upper eyelids are affected, but the lower eyelids may also have coloboma. It’s also possible for all four eyelids (both upper and lower) to be affected.
Blurry vision or blind spots
People with retina coloboma can experience vision loss in specific areas of the visual field. This is known as scotoma or blind spots. The upper region of the visual field is usually affected. However, if the coloboma interferes with the optic disc, central vision may diminish or be lost.
Blurry vision can also occur with lens coloboma. This is because the lens is the focusing structure of the eye. If part of it is missing, its focusing ability may be affected.
Light sensitivity
Photophobia (light sensitivity) is most common with iris coloboma. This is because the pupil controls how much light enters the eye. To let more light in, the pupil will get bigger (dilate). It will constrict, or get smaller, to reduce the amount of light entering the eye.
Because part of the iris is missing due to the coloboma, the pupil’s constriction isn’t as effective. This can make people with iris coloboma sensitive to light in bright conditions due to glare, discomfort and reduced visual clarity.
How doctors check for coloboma
A pediatric eye doctor will first do a physical exam of the baby’s eyes. Iris and eyelid coloboma can often be diagnosed during physical examination.
To examine the inside of the eye, they may use dilating eye drops to get a better look at the internal structures. Using a tool called an ophthalmoscope, they will check to see if colobomas are present inside the eye.
Unless visible signs of coloboma are present at birth, an eye doctor may not check for coloboma inside the eyes until later in life. In other words, if an iris or eyelid coloboma isn’t present to alert the eye doctor to a problem, it may take more time to diagnose.
Living with coloboma
Treatment options depend on the type of coloboma that you have. For those looking for coloboma treatment, successful methods for each type include:
- Iris coloboma – Iris coloboma can be surgically treated by having the iris sutured, essentially closing the gap. A less invasive option includes wearing color contact lenses to cover the coloboma.
- Lens coloboma – Surgery to replace the affected lens can treat lens coloboma. It can also treat or prevent cataract formation that often occurs with lens coloboma. Besides surgery, corrective glasses or contacts may help improve vision in the affected eyes.
- Retinal coloboma – Surgical procedures are available to treat complications associated with retinal coloboma. These may include retinal detachment, blood vessel overgrowth and cataracts.
- Optic nerve coloboma – No treatment is available to treat optic nerve coloboma. Low vision aids are available to help those whose vision has declined due to the condition.
- Eyelid coloboma – Eyelid coloboma may be treated surgically to create a full eyelid. It can also be managed with products designed to protect and moisten the eye.
If only one eye is affected with coloboma, an eye doctor may recommend measures to avoid amblyopia (lazy eye). These measures can include wearing an eye patch over the better eye to help strengthen the affected eye. Glasses or prescription eye drops may also be used.
Problems coloboma can cause
Having coloboma can increase a person’s risk of developing other eye diseases. Some of these include:
Cataracts
Cataracts occur when the naturally clear lens of the eye becomes cloudy. The cloudiness can affect the vibrancy and detail of a person’s vision. If left untreated, the cataracts can grow and ultimately lead to vision loss.
Glaucoma
Glaucoma is a series of eye diseases characterized by damage to the optic nerve. It’s often associated with increased pressure in the eye. Over time, the increased pressure can press on the optic nerve. This can lead to nerve damage and vision loss.
Retinal detachment
Retinal detachment is a condition in which the retina pulls away from the back of the eye. The retina is a light-sensitive tissue that lines the back of the eye and is essential for vision. If not treated quickly, retinal detachment can lead to permanent vision loss or blindness.
When to see your eye doctor
Some people with minor coloboma may never experience vision problems, so it’s important to get regular comprehensive eye exams. If any eye structures are missing tissue, their health and function may be affected. Your eye doctor will check your eyes for these types of abnormalities (and others) during each exam.
If you’ve been diagnosed with eye coloboma, see an eye doctor right away if you notice changes in your vision. Routine eye exams can help ensure your vision and eye health are at their best.
