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Congenital glaucoma

Summary
Aetiology
Clinical features
Diagnosis
Management
References
Author(s)

Summary

Primary congenital glaucoma (PCG) is a rare condition (incidence of 1:10,0000), caused by maldevelopment of the trabecular meshwork (trabeculodysgenesis) and anterior chamber angle, resulting in impaired aqueous outflow and raised intraocular pressure (IOP), without other ocular or systemic developmental anomalies.

Aetiology

There are three types:

True congenital glaucoma (40% of cases) - IOP is elevated intrauterine
Infantile glaucoma (55% of cases) - manifests prior to age 3
Juvenile glaucoma - the least common, manifests between age 3 and 16.

Cases are usually sporadic, however approximately 10% of cases are autosomal recessive with a variable penetrance. The main gene culprit has been implicated is the CYP1B1 gene. This gene codes for an enzyme that metabolises vital components for ocular development, and Teixeira et al found that in mouse models severe trabecular meshwork atrophy is seen in subjects with a gene deletion.

The MYOC gene on chromosome 1q24 may also explain some cases of PCG, although it is classically associated with primary open angle glaucoma.

Prognosis depends on severity and the age at onset, in true congenital glaucoma, legal blindness happens in at least 50% of eyes.

Primary congenital glaucoma is the most common form, and one of two primary childhood glaucomas presenting in children under four (the other being juvenile open angle glaucoma). If another disease process is present, we can rule out PCG, and other diagnosis need to be considered (e.g. Axenfeld Reiger syndrome, aniridia, Peters anomaly, persistent fetal vasculature, Sturge Weber syndrome, Lowe syndrome, retinopathy of prematurity, tumours and many others).

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The 2013 International Classification System for Childhood Glaucoma defines childhood glaucoma as irreversible or reversible damage to the whole eye (not just the optic nerve as glaucoma is defined for adults). Therefore, the following clinical signs affecting the whole eye are important to make a diagnosis.

Clinical features

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The classic triad of primary congenital glaucoma is 1) photophobia, 2) epiphora and 3) blepharospasm.

Corneal haze: Due to diffuse oedema secondary to raised IOP, or localized oedema

Buphthalmos: A large eye which occurs as a result of stretching due to elevated IOP before the age of 3 - the thinned sclera appears blue due to increased visualisation of the uvea underneath.

Haab striae: Curvilinear healed breaks in the Descemet membrane

Corneal scarring/vascularization

Optic disc cupping

Diagnosis

IOP measurement should be performed first, and where possible this should be measured in a conscious or sedated child. The instrument of choice in young children is the Perkins applanation tonometer - and in older children the standard Goldmann applanation tonometry can be used. The normal IOP in infants and young children is lower than in adults. A newborn has an average IOP of 10-12 mm Hg, which goes up to around 14 mm Hg by age 7 or 8. Any asymmetric or elevated measurements combined with other suggestive eye signs helps clinch the diagnosis.

Anterior chamber examination can be carried with an operating microscope or portable slit lamp, which may reveal Haab striae. Upon optic disc examination, asymmetry or a cup/disc ratio of >0.3 may be clinically significant, and corneal diameter measurement: > 12 mm prior to the age of one year is also suspicious.

Gonioscopy using a direct goniolens may reveal trabeculodysgenesis - appearing as an anteriorly located iris insertion and a hypoplastic appearing peripheral iris.

Management

Surgical management is essential: angle surgery alone is successful in 80-90% of cases. Medication may be used as a temporary or supplementary therapy - in young children however caution must be exercised as many medications are contraindicated. Ambylopia and refractive error must be aggressively managed to prevent long term visual defects.

Options for angle surgery include goniotomy or trabeculotomy, which improve aqueous outflow resulting in a lowered IOP. Goniotopy is often done in the first instance, with trabeculotomy if corneal haze prevents a clear view or if goniotomy has failed.

Goniotomy: Under direct gonioscopic visualization an incision is made at the midpoint of the trabecular meshwork

Trabeculotomy: A partial thickness scleral flap is created and a trabeculotome is inserted into the Schlemm canal and rotated into the anterior chamber.

Trabeculectomy, tube shunt implantation, and ciliary body ablation.

IOP and corneal diameter must be monitored long term.

References

Bowling, Brad. Kanski’s Clinical Ophthalmology: A Systematic Approach 2016. Open WorldCat, http://public.ebookcentral.proquest.com/choice/publicfullrecord.aspx?p=2029294.
Papadopoulos M, Cable N, Rahi J, Khaw PT. The British Infantile and Childhood Glaucoma (BIG) Eye Study. Invest Ophthalmol Vis Sci. 2007;48(9):4100-6
Teixeira LB, Zhao Y, Dubielzig RR, Sorenson CM, Sheibani N. Ultrastructural abnormalities of the trabecular meshwork extracellular matrix in Cyp1b1-deficient mice. Vet Pathol. 2015;52(2):397-403.

Author(s)

Dr Sara Memon

Sara is the Co-Founder of Ophtnotes. She is a doctor who graduated from UCL Medical School in London. She won the Allen Goldsmith Prize in Ophthalmology. Sara is also the co-founder of PAMSA: an organisation linking doctors and medical students of Pakistani origin. She’s especially passionate about teaching and education, having presented a workshop she designed herself at the 2019 Annual GMC Conference.