Megalocornea is a rare condition in which the cornea is larger than usual. In primary congenital megalocornea, the enlarged corneas are present from birth and the intraocular pressure is not raised.
The condition is usually bilateral, meaning it affects both eyes. It is important to distinguish megalocornea from congenital glaucoma, because glaucoma involves raised eye pressure and needs different management.
Features
Megalocornea is usually defined by an enlarged horizontal corneal diameter, often at least 12.5 to 13 mm. The cornea is enlarged but typically clear.
Common or recognised features include:
- enlarged corneal diameter
- deep anterior chamber
- mild to moderate short-sightedness in some people
- light sensitivity
- iridodonesis, where the iris trembles because support structures are abnormal
- lens dislocation or lens instability in some cases
- cataracts developing earlier than usual in some adults
- risk of secondary glaucoma in some people
Visual outcome varies. Some people have relatively good vision with monitoring and correction, while others develop complications that need specialist eye care.
Cause and Inheritance
Isolated congenital megalocornea is most often linked to pathogenic variants in the CHRDL1 gene. CHRDL1 is located on the X chromosome and is involved in eye development.
The recognised isolated form is usually inherited in an X-linked recessive pattern. This means males are more commonly affected, while carrier females may have no symptoms or milder findings.
Megalocornea can also appear as part of broader syndromes or other eye-development disorders. When other features are present, clinicians may look for a wider genetic or developmental diagnosis.
Diagnosis
Diagnosis is clinical and is made by eye examination. The key findings are enlarged corneas and a deep anterior chamber without the raised intraocular pressure expected in congenital glaucoma.
Assessment may include:
- corneal diameter measurement
- intraocular pressure measurement
- slit-lamp examination
- optic nerve assessment
- refraction testing
- imaging of the front of the eye
- genetic testing when an inherited form is suspected
Family history can help, especially when an X-linked pattern is possible.
Management
Management depends on symptoms and complications. Some people need monitoring only, while others need treatment for refractive error, cataract, glaucoma or lens problems.
Care may include glasses or contact lenses, regular eye-pressure checks, cataract monitoring, glaucoma surveillance and advice before eye surgery. Surgery can be more complicated because the front part of the eye has unusual dimensions.
Differential Diagnosis
The main condition to distinguish from megalocornea is primary congenital glaucoma. Both can involve large corneas, but congenital glaucoma is usually associated with raised intraocular pressure and may cause corneal clouding, tearing and sensitivity to light.
Other conditions that may be considered include anterior segment dysgenesis, corneal enlargement linked to systemic syndromes, Marfan syndrome, Down syndrome and other inherited eye disorders.
See Also
References
Discussion log
Use comments for sourcing notes, corrections, and disputed details.
No comments yet.