Megalocornea is a congenital developmental anomaly characterized by a corneal diameter larger than normal, with intraocular pressure, fundus, and visual function remaining within normal ranges. When not accompanied by other abnormalities, it is referred to as simple megalocornea. The condition follows an X-linked recessive inheritance pattern, with the genetic locus identified on Xq21.3-q22.
The majority of individuals with megalocornea are male, and the condition is typically bilateral, symmetric, and nonprogressive. Horizontal corneal diameters exceed 13 mm, and vertical diameters exceed 12 mm, with disproportionate enlargement of the anterior segment of the eye. The cornea appears clear, and the corneal limbus has well-defined boundaries. In some cases, other ocular abnormalities, such as defects in the iris, ciliary body, pupil, or lens, may be present, or there may be associated systemic congenital anomalies such as Marfan syndrome, in which case the condition is also referred to as anterior megalophthalmos.
In diagnosing megalocornea, differentiation from congenital glaucoma is necessary. The latter presents with an enlarged, cloudy cornea, expanded and poorly defined corneal limbus, elevated intraocular pressure, among other features.