Introduction
Background
Megalocornea is a nonprogressive enlargement of the cornea to 13 mm or greater. The cornea and the limbus are enlarged, but the cornea itself is histologically normal. Megalocornea is usually seen as an isolated finding, but it may be associated with other ocular and systemic findings. The additional ocular findings are found in anterior megalophthalmos, which includes an enlarged ciliary ring and crystalline lens in addition to an enlarged cornea.
Pathophysiology
Megalocornea is a developmental anomaly of unknown etiology. Postulated mechanisms of development include a defect in formation of the optic cup in which the anterior tips of the cup fail to fuse, allowing more space for the developing cornea, spontaneous arrest of congenital glaucoma, and exaggerated growth of the cornea. Abnormal collagen synthesis may play a role.
Frequency
United States
No data are available.
International
No data are available.
Mortality/Morbidity
- Morbidity and mortality can be secondary to the many systemic conditions found in association with megalocornea. See Special Concerns.
- Ocular morbidity is associated with anterior megalophthalmos. An enlarged ciliary ring causes zonular stretching, leading to phacodonesis, ectopia lentis, iridodonesis, iris stromal hypoplasia and transillumination defects, Krukenberg spindles, and trabecular meshwork pigmentation. Other findings are posterior embryotoxon, Rieger anomaly, goniodysgenesis, and cataracts. Goniodysgenesis and pigment dispersion can contribute to glaucoma.
Sex
Males account for 90% of cases because X-linked recessive inheritance is most common.
Age
Megalocornea is present from birth.
Clinical
History
- Megalocornea is present from birth.
- A family history of megalocornea may be present.
- The mother may have slightly enlarged corneas.
Physical
- Simple megalocornea
- Usually bilateral
- Usually good visual acuity
- With-the-rule astigmatism common
- Corneal diameter usually 13.0-16.5 mm
- Corneal thickness normal and stroma clear. May have central mosaic dystrophy (see Media file 1).
- Limbus sharply demarcated
- Keratometry usually normal but may be steeper than normal
- Anterior chamber depth increased
- Lens-iris diaphragm positioned posteriorly
- Vitreous length short
- Intraocular pressure normal
- Anterior megalophthalmos
- Megalocornea
- Ciliary body band wider than the trabecular meshwork and scleral spur on gonioscopy
- May have any of the following:
- Iridodonesis
- Iris stromal hypoplasia
- Transillumination defects
- Phacodonesis
- Ectopia lentis
- Cataracts
- Krukenberg spindles
- Posterior embryotoxon
- Excessive mesenchymal tissue in the angle
- Glaucoma (but not congenital glaucoma)
- Findings of congenital glaucoma not found in megalocornea
- Elevated intraocular pressure
- Corneal edema and Haab striae
- Optic disc cupping
Causes
- Megalocornea is inherited as an X-linked recessive trait (90% of cases).
- The gene locus for X-linked megalocornea is in band Xq12-q26, most likely band Xq21-q23.
- Autosomal dominant, autosomal recessive, and sporadic inheritance have been reported.
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References
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Further Reading
Keywords
enlarged cornea, corneal enlargement, anterior megalophthalmos, cataracts, glaucoma
