An Infant With Enlarged Corneas

Marjan S. Bolouri; Aaron M. Miller, MD; David K. Coats, MDSeries Editor: David K. Coats, MD

Disclosures

September 14, 2006

Discussion

Congenital megalocornea is a rare inherited enlargement of the corneas often associated with dysgenesis of the trabecular meshwork, iris, or both. The pathophysiology of primary megalocornea is not completely understood, but it is believed to be linked to induction of the lens during embryologic development of the anterior chamber.[1]

The differential diagnosis of large corneas in a child includes glaucoma, primary megalocornea, and keratoglobus. Distinguishing primary megalocornea from other causes is essential to planning proper treatment. Children with congenital glaucoma and keratoglobus are at risk for progressive corneal enlargement or rupture and thus require intervention, whereas treatment is unnecessary for primary megalocornea.

Studies of children with megalocornea have revealed a number of clinical features that differentiate this entity from congenital or infantile glaucoma.[2] Megalocornea is characterized by large corneas with normal IOP, transilluminating defects of the iris, pigment dispersion, and absence of breaks in Descemet's membrane (Haab's striae). The corneas are typically larger than 12 mm in diameter at birth, and larger than 13 mm in diameter by 1 year of age. The anterior chambers are usually very deep, with depth exceeding the mean value plus 2 SD, while vitreous length is typically short. A study of 11 males with megalocornea found smaller keratometry readings, an observation termed globular corneas, which may be pathognomonic for megalocornea.[3]

In congenital glaucoma, the elevated IOP causes photophobia, epiphora, eye pain, corneal opacification, and tears in Descemet's membrane — findings not encountered in primary megalocornea.[2] Also in contrast to megalocornea, congenital glaucoma is marked by elevated IOP, absence of iris transillumination defects, absence of pigment dispersion, and less pronounced enlargement of the anterior segment. Because asymmetric corneal enlargement may be found in primary megalocornea as well as congenital glaucoma, this sign may not be used to reliably differentiate between these conditions.

Megalocornea is inherited in an X-linked recessive pattern, and the gene locus for megalocornea has been mapped to the Xq21.3-q22 region.[4,5] This pattern is in contrast to congenital glaucoma, which demonstrates autosomal recessive inheritance in most familial cases.[6] The variability in findings and severity among reported cases of congenital megalocornea, however, has raised the possibility of heterogeneity, and autosomal recessive and dominant inheritance patterns have been described.[7]

Megalocornea may present as part of the megalocornea-mental retardation syndrome (MMR), first described by Neuhauser and colleagues in 1975.[8] Also known as Neuhauser syndrome, over 30 patients have been described, 88% of which have megalocornea. Familial occurrence suggests an autosomal recessive inheritance.[9,10] Due to clinical variability, patients with the syndrome may also present with macrocephaly and motor retardation in what is known as megalocornea, macrocephaly, mental and motor retardation, or MMMM syndrome.[11,12]

Comments

3090D553-9492-4563-8681-AD288FA52ACE
Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.
Post as:

processing....