Megalocornea - Causes, Symptoms, Diagnosis, and Treatment

Introduction:

The eye is an essential sense organ mainly consisting of the cornea, pupil, iris, lens, and retina. The cornea is the clear and transparent layer covering the eye's iris, pupil, and anterior chamber. The interesting fact about the cornea is that it does not contain blood vessels like other tissues. Instead, it obtains nutrients from tears and the eye's anterior chamber (fluid-filled portion). The cornea works by bending and focusing the light that enters the eye. This article reviews the rare corneal defect.

What Is Megalocornea?

Megalocornea is a rare congenital defect characterized by enlargement of the diameter of the cornea in both eyes. The increased corneal diameter is non-progressive and is more than 12.5 to 13 mm. In addition, the eye (intraocular) pressure remains normal. The other names of megalocornea are:

• X-linked megalocornea.

• Macrocornea.

• Anterior megalophthalmos.

How Is Megalocornea Caused?

• The specific cause of megalocornea is unknown. It may be associated with other conditions or genetic changes (mutation).

• Our body consists of 23 pairs of chromosomes that carry the genetic material called DNA (deoxyribonucleic acid). Out of which 22 pairs are growth chromosomes and one pair of sex chromosomes (X and Y). Males have one X and one Y chromosome, while females have two X chromosomes.

• The chordin-like 1 (CHRDL1) gene present on the X-chromosome is responsible for producing a protein called ventroptin. It works against the bone morphogenic protein (BMP) and aids in corneal development. The defective Chordin-like 1 gene leads to the lack of ventroptin production, which generates bone morphogenic protein buildup. It eventually gives rise to unregulated growth of cornea leading to megalocornea. It more commonly affects males than females.

What Are the Signs and Symptoms?

The megalocornea develops by birth, and it leads to the following:

In Children -

• Usually asymptomatic.

• Blurred vision; usually occurs due to astigmatism (unusual curvature of the cornea).

In Adults -

• Glaucoma: The increased pressure in the eye damages the optic nerve leading to an eye condition called glaucoma. Individuals over 60 years of age have an increased risk of developing glaucoma. Initially, it does not show any symptoms. Severe pain, redness of the eye, headache, and blurred vision may develop later.

• Mosaic corneal dystrophy occurs due to a buildup of foreign substances in the cornea and causes blurred vision.

• Cataract (cloudy lens): Individuals between 30 years to 50 years of age are usually affected.

• Arcus juvenilis: A gray or bluish arc around the cornea that is made up of fatty substances (mainly cholesterol).

• Lens subluxation: The lens is malpositioned from its usual location.

Other Conditions Include-

• Iris atrophy: It is characterized by the degeneration of the colored portion of the eye.

• Lens dislocation.

• Retinal detachment is a severe condition where the retina (inner layer of the eye) is disconnected from its original position. If left untreated, it leads to complete blindness.

• Coloboma: The normal tissues in the iris, pupil, or other eye parts are missed at birth.

• Zonular fibers abnormalities: The zonular fibers of the eye aids in holding the lens in its position. Any defect in zonular fibers leads to blurred vision.

• Uneven or asymmetrical cornea.

How to Diagnose Megalocornea?

The diagnosis of megalocornea provides a significant challenge as the children are primarily asymptomatic. However, the following techniques are used in evaluating megalocornea.

• Clinical Examination: The ophthalmologist utilizes a slit-lamp tool to examine the eye's cornea, lens, and anterior chamber. The visualized features of megalocornea include-

1. Deep anterior chamber.
2. The corneal diameter is more than 13 mm.
3. Decrease in the vitreous chamber (fluid-filled space behind the eyeball) length.
4. Iris and the lens are pushed backward.
5. The trabecular meshwork is a spongy tissue where the fluid from aqueous humor drains out of the eye. It looks severely pigmented in megalocornea.

• Electroretinogram: It is a test used to measure the retina's response to light. In a few individuals with megalocornea, the cells that perceive color are affected.

• Visual Evoked Potential: An electric conductor is placed on the back of the head, and its response to a visual stimulus (image) is measured. There is a delay in transmitting optical signals in patients with megalocornea. However, intellectual abilities remain normal.

• Genetic Testing: A specific test identifies alterations in the genes and chromosomes. It is considered a confirmatory test to detect the changes in X-chromosomes.

What Are the Related Disorders?

The conditions that consist of features similar to megalocornea are as follows-

• Infantile Glaucoma: It is a rare disorder that affects the drainage of aqueous fluid out of the eye. Therefore, the fluid gets accumulated and increases the intraocular pressure. It usually affects infants and children. On clinical examination, it shows features similar to that of megalocornea.

• Neuhauser Syndrome: It is a congenital disorder that causes mental retardation, megalocornea, muscle weakness, and facial deformities.

• Frank-Ter-Haar Syndrome is an inherited disorder characterized by a large cornea, skeletal abnormalities, and developmental delay.

How to Treat Megalocornea?

No specific treatment cures megalocornea. However, disorders associated with it have managed to reduce symptoms.

It includes:

• Corrective lenses, glasses, or surgery is suggested to correct mild vision problems. The patients are followed-up regularly.

• Correction of cataracts is complex and is done with great care as the complication after the surgery is high.

• Eye drops and oral medications combined with or without surgery reduce the intraocular pressure (IOP) in glaucoma.

• Iris-claw intraocular lens (IOL) is used after cataract surgery and is clipped to the iris to maintain the lens position.

Conclusion:

Megalocornea is a rare genetic defect, and its symptoms usually remain mild. The prognosis of it is significantly good with proper and early treatment. It also provides a significant challenge to the professionals in the diagnosis, but genetic testing is done to confirm such defects. The parents of the affected children are also informed about the complications of megalocornea in later life. Therefore, the affected children need support from parents and specialists to lead better lives.