Congenital Primary Glaucoma

There are various forms of congenital glaucoma. Some arise in the context of other abnormalities (e.g. Reiger's syndrome, Sturge-Weber syndrome and neurofibromatosis) but the commonest type of infantile glaucoma is in fact primary congenital glaucoma. In 90% of cases, this is sporadic and in the remaining 10% of cases, there is an autosomal dominant pattern of inheritance.¹

The problem lies in defective aqueous outflow from the anterior chamber due to malformation of the trabecular meshwork, the main drainage passage for aqueous. This results in a rise in intraocular pressure (IOP): in true congenital glaucoma (40% of cases), this occurs during intrauterine life and in infantile glaucoma (55% of cases), the rise is evident before the child's third birthday. The remainder of cases fall into the juvenile glaucoma group whose problem manifests itself after the third birthday but before the age of 16.²

Most cases (75%) are bilateral although involvement is usually asymmetrical.

• This is the most common of the congenital glaucomas but is still very rare, of the order of 1:10,000 births.
• 65% of patients are boys.
• Its impact, if unrecognised, can be significant on the child's vision: it accounts for about 2-15% of patients being treated / cared for by institutions for the blind.³

This depends on the age of onset of IOP rise but general trends are common to all children.

Symptoms

• Corneal changes including oedema which causes haziness. This may be the first abnormality noticed by the parents.
• Globe enlargement (if the IOP rises before the age of 2), known as buphthalmos. This is not generally noticed by parents unless it is unilateral or markedly asymmetrical, when they may report that their child has a 'large eye'.
• Other highly significant symptoms are photophobia, epiphora and blepharospasm.

Signs

The ophthalmologist will make a note of the following:

• Presence of buphthalmos
• Corneal diameter: a horizontal diameter of > 12mm before the first year of life is highly suggestive.³
• Abnormalities of one of the layers of the cornea (Descemet's membrane) which can split so causing corneal oedema.
• A rise in IOP
• Abnormalities on examination of the trabecular meshwork
• Optic disc cupping
• Refractive changes - particularly myopia (short-sightedness)

• Cloudy cornea at birth - birth trauma, intrauterine rubella, some metabolic disorders (e.g. mucopolysaccharidoses), congenital corneal dystrophies.
• Large cornea - very high myopia, megalocornea.
• Epiphora - delayed canalisation of the nasolacrimal duct (very common).
• Raised IOP - tumours (e.g. retinoblastoma), retinopathy of prematurity, intraocular inflammation, trauma.

This depends on the age of the child. The ophthalmologist will need to ascertain the visual acuity, the IOP and have a good look at the trabecular meshwork as well as the fundus via dilated fundoscopy. Visual acuity can be determined to a certain extent when the child is awake but a full examination of the globe usually warrants a general anaesthetic.

By definition, this condition occurs in an otherwise healthy eye with no associated systemic disease.

• Primary care - any child presenting with symptoms or signs suggestive of glaucoma should be referred to the ophthalmologists. If the child appears to be systemically unwell (irritable, not feeding), referral should be immediate. If the symptoms have been going on a while, discuss it with the duty ophthalmologist.
• Medical⁴ - this is usually temporary and initiated on diagnosis whilst awaiting surgery. It may involve the use of topical beta-blockers ± systemic carbonic anhydrase inhibitors.
• SurgicalSurgery is the definitive treatment and can involve one or more of the following:
  • Goniotomy - this is usually performed at the initial examination under anaesthetic once the diagnosis is confirmed. It involves opening Schlemm's canal (which drains the aqueous) via an incision into the trabecular meshwork. This procedure may need to be repeated more than once.
  • Trabeculotomy - this is similar to the above procedure but uses a different technique; it is used when the cornea is too cloudy to allow for a goniotomy.
  • Trabeculectomy - this involves removal of part of the trabecular meshwork (or where it would be if it were correctly formed) in order to allow aqueous to drain into Schlemm's canal.
  Where these procedures fail, a modified trabeculectomy is performed, using antimetabolite drugs such as 5FU or mitomycin C.
• Intractable glaucoma - this may be treated with laser therapy or cryotherapy but this is very much a last resort.
• Optical - any refractive errors will also be addressed in order to minimise the possibility of amblyopia.

Undiagnosed glaucoma can lead to life-long visual impairment. However, this is quite unusual as most cases are picked up. The most serious complications are rare but tend to relate to having a general anaesthetic or to the surgery itself (hyphaema, infection, lens damage and uveitis).

The corneal oedema may persist for several weeks but often resolves as does the optic disc cupping (unlike adults). However, parents (and eventually, patients) need to be aware that there is always a risk of the pressure rising again and they will need life-long monitoring.⁴ About 50% of patients are left with a degree of visual loss² which may be due to persistent oedema, persistent optic disc cupping, nystagmus, large refractive errors or amblyopia. An enlarged globe will also be more susceptible to damage in the future.