Why you need to beware of potential mimickers of paediatric glaucoma

Reviewed by Gabor Hollo

Take-home: Some rare paediatric conditions can be mistaken for early childhood glaucoma.

Primary congenital glaucoma (isolated goniodysgenesis) is often a straightforward diagnosis. Classic phenotypic features include increased measured IOP, corneal haze/scarring with associated astigmatism, corneal enlargement (megalocornea) with globe enlargement (buphthalmos) and associated myopia, Descemet membrane breaks (Haab striae), iris atrophy and optic nerve cupping. These findings also occur in early developmental glaucoma. However, although the diagnosis of primary congenital or early developmental glaucoma is usually straightforward, similar phenotypic features can occur in other paediatric conditions, which are sometimes mistaken for early childhood glaucoma. Ophthalmologists who care for children with glaucoma must keep such potential mimics of paediatric glaucoma in mind.

False increases in measured IOP

False increases in measured IOP

Cooperation issues

Although it is desirable to obtain an IOP measurement in a child with suspected glaucoma, a child who is struggling and/or squeezing his or her eyelids will have a falsely elevated reading. Examination under general anaesthesia can also result in falsely raised IOP values, depending upon the agents used (e.g., ketamine can increase IOP), the degree of discomfort experienced by the child during the examination (e.g., from a large speculum or only partial anaesthesia) and/or the degree of intrathoracic pressure from endotracheal intubation. For uncooperative or very young children, IOP measurements can be taken while the child is sleeping (often after feeding) or, if necessary, under sedation with an agent such as chloral hydrate.

Corneal disease and megalocornea

Corneal disease

The right eye of a 10-year-old boy with genetically-proven congenital hereditary endothelial dystrophy is show. Measured intraocular pressures were in the high twenties but there were no glaucomatous changes and follow-up examination have been stable.

Sometimes corneal diseases can cause falsely elevated IOP readings, making them challenging to distinguish from glaucoma. In aphakia, for example, corneas are often abnormally thick. In primary corneal disease such as congenital hereditary endothelial dystrophy, corneal haze is sometimes accompanied by falsely elevated IOP readings. In such cases the lack of other glaucomatous signs (such as Descemet breaks, globe enlargement and disc cupping) should raise suspicion. In addition to primary corneal disease such as congenital hereditary endothelial dystrophy, corneal haze without glaucoma can also occur in metabolic diseases such as mucopolysaccharidoses.

Megalocornea

This baby boy with X-linked megalocornea had large horizontal corneal diameters (14 mm) but no corneal haze, Descemet breaks, or other signs for glaucoma. Follow-up examinations have been stable and maternal male cousins with similar findings were identified.

Megalocornea or anterior megalophthalmos refers to an enlarged anterior chamber with a cornea greater than 13 mm in horizontal diameter and without Descemet breaks or scarring. A stromal mosaic appearance (shagreen) is sometimes a feature of megalocornea; while its presence is helpful in making the diagnosis, its absence does not rule out the condition. Posterior bowing of the iris is another anterior segment sign that can be helpful in distinguishing megalocornea from buphthalmic changes. Measuring the ratio of anterior chamber depth to axial length can also be helpful: a large ratio (≥0.20) is typical for megalocornea but not expected in buphthalmos.

Descemet breaks and optic nerve cupping

Descemet breaks

Use of forceps during childbirth can cause compression of the globe between the roof of the orbit and the blade of the obstetric forceps, which may initially be overlooked because of lid oedema. Associated tears in the Descemet membrane are unilateral and generally appear as vertical or oblique striae that are parallel, with straight edges; they are associated with astigmatism. Rare corneal disease can also be associated with Descemet breaks or bands. In brittle cornea syndrome, corneal ectasia can result in Descemet breaks. In posterior polymorphous corneal dystrophy, metaplasia and overgrowth of endothelial cells result in characteristic vesicles and bands at the level of the Descemet membrane.

Optic nerve head cupping

The classic “vacant disc” of a 10-year-old girl with papillorenal syndrome is shown (right eye). Note the characteristic absence of central disc vessels. She had hypoplastic kidneys.

Although optic nerve head cupping is a feature of uncontrolled paediatric glaucoma, there are developmental causes of optic nerve cupping that are not glaucomatous. In papillorenal syndrome, abnormal vasculogenesis of the central retinal artery results in a characteristic ‘vacant’ appearance to the optic nerve head (and renal abnormalities). A unique form of optic nerve hypoplasia occurs in periventricular leukomalacia, which manifests primarily as cupping. In children with megalopapilla, optic nerve cups are large, which maintains the normal neuroretinal rim area.

Summary

Summary

The diagnosis of early childhood glaucoma is usually straightforward. However, paediatric ophthalmologists must always keep in mind conditions that can be mistaken for glaucoma. In my experience, confusion most often occurs in infants with isolated megalocornea, congenital hereditary endothelial dystrophy and optic nerve hypoplasia that is related to perinatal brain hypoxia and manifests as optic disc cupping.

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 Dr Arif O. Khan

E: arif.khan@mssm.edu

Dr Arif Khan is a paediatric ophthalmologist and ocular geneticist at the Eye Institute of Cleveland Clinic Abu Dhabi in the United Arab Emirates.