Congenital Glaucoma: What Optometrists Need to Know

Childhood glaucoma can be broadly classified into primary and secondary types (Figure 1). Congenital glaucoma constitutes a diverse group of diseases, in which a structural anomaly in the drainage angle, present at birth, results in impaired aqueous outflow and elevated intraocular pressures (IOP).^1,2

This article will focus on primary congenital glaucoma (PCG) – the most prevalent subtype where the angle anomaly occurs in the absence of an associated ocular or systemic condition. PCG presents before three years of age, with most cases (80%) presenting in the first year of life.^2,3 The incidence of PCG varies across different populations, however the average is one in 10,000 live births.⁴ In Australia, the reported incidence is one in 30,000 births.⁵ Although PCG can occur sporadically, causative genes have been identified and the incidence appears to increase with consanguinity.⁶ The condition is mostly bilateral and can be asymmetric.⁷

Figure 1. The basic classification scheme of paediatric glaucoma based on the Childhood Glaucoma Research Network (CGRN) classification system.

CLINICAL PRESENTATION

The clinical presentation of PCG is variable and determined by the age of onset and degree of IOP elevation. The most severe form of PCG is present between birth and the first month of life (25% of cases).⁸

Anterior Eye

PCG is typically characterised by the triad of epiphora, photophobia, and blepharospasm – all secondary to IOP-induced corneal oedema and the associated loss of corneal transparency. The oedema initially involves the corneal epithelium, however with prolonged IOP elevation, extends to the stroma, resulting in irreversible scarring/opacification.⁹ Infants with photophobia have an aversion to standard lighting and involuntarily close, shield, excessively blink, or rub their eyes.

The elastic nature of the scleral and corneal collagen fibres in the first three years of life means the immature eye can respond to elevated IOPs by progressive enlargement of the globe (buphthalmos), with the main enlargement occurring at the corneoscleral junction (Figure 2). Corneal diameters suggestive of elevated IOPs vary with age (Table 1).^3,10,11 Corneal enlargement may give way to single or multiple breaks in the less elastic Descemet’s membrane known as Haab striae, or descriptively as ‘tram tracks’ (Figure 3). Other causes of breaks in Descemet’s membrane must be differentiated (Table 2).^2,4,9 The differential diagnosis of PCG should also be considered (Tables 3, 4).¹¹

Intraocular Pressure

The IOP in a healthy infant eye is less than 12mmHg.¹² An IOP above 21mmHg or an asymmetry of 5mmHg in a calm resting infant raises the suspicion of glaucoma.^2,3

While the mainstay of treatment is surgical in nature, primary eye care practitioners also play a pivotal role in minimising the impact on vision

However, IOP can be one of the most variable and least accurate parameters when assessing an infant for glaucoma, and hence diagnosis should not be based on IOP alone. Eye movements, crying, eyelid squeezing, breath-holding, resistance or the use of a lid speculum will falsely elevate the IOP.^2,8,12

An elevated IOP in conjunction with any of the key clinical features of PCG (Table 5), warrants an urgent referral to a paediatric ophthalmologist/glaucoma specialist. If an accurate IOP measurement is not possible, any combination of the key features also warrants immediate referral.

Optic Disc Cupping

In the absence of a congenital optic disc disorder, a cup-to-disc ratio ≥ 0.3 or an asymmetry greater than 0.2 is suggestive of congenital glaucoma.^3,14

The pattern of optic disc cupping in PCG differs from that in adult glaucoma in two ways:

1. In infants, the cupping tends to be round and enlarges circumferentially (vertical oval elongation in adults), and
2. Reversal of cupping can occur with normalisation of IOP in the early stages of PCG – especially in the first year of life where the laminar cribrosa is most elastic.

Any pre-treatment retinal nerve fibre layer loss tends to be permanent. An increase in disc cupping indicates poorly controlled glaucoma, regardless of the IOP measurement.^15-17

CLINICAL EXAMINATION

Optometrists may be the first to detect changes indicative of PCG. An unusual appearance to the baby’s eyes or their behaviour usually prompts parents to consult an eye care practitioner or referral from a paediatrician.

A comprehensive ocular examination may be a challenge given the age group; however, strategies can be implemented to facilitate a more successful paediatric examination. Swaddling, during or shortly after bottle feeding, may help calm/distract the baby for the examination. Dim ambient lighting may also assist, especially for those with photophobia. Quick, simple testing techniques with good fixation targets (e.g., bright coloured/light up toys) work well.

In almost all cases, an ophthalmologist will need to conduct an examination under general anaesthesia in the operating theatre.²

Nevertheless, the initial assessment is essential to establish enough evidence to justify timely referral, and would include:

1. History: family history of glaucoma, parental consanguinity, associated congenital defects, birth history,
2. External eye examination: enlargement, asymmetry, corneal transparency/size, behaviours,
3. Age-appropriate visual acuity assessment,
4. Pupillary responses,
5. Ocular motilities: penlight/bright coloured toy,
6. Ocular alignment: cover test using thumb to occlude/Hirschberg test,
7. Retinoscopy: look for myopia,
8. Anterior eye examination: handheld slit lamp. Look for corneal oedema, scarring, Haab striae, anterior chamber abnormalities,
9. Ophthalmoscopy: observe red reflex, cup-to-disc ratio, and
10. Tonometry using a handheld device.
11. Perkins applanation tonometry is the most accurate. Tonopen and I-care tonometers overestimate the IOP in this cohort.¹⁹ I-care may be an advantage as it does not require topical anaesthesia, however the child needs to be upright.

The ophthalmological examination under anaesthesia would likely include the following additional components to confirm the diagnosis and establish an accurate baseline:

• Corneal diameter measurement with callipers,
• Axial length measurement with a-scan ultrasonography,
• Corneal pachymetry,
• Gonioscopy,
• Cycloplegic refraction,
• Dilated fundus examination,
• Fundus photo, and
• B-scan ultrasound if visualisation of the posterior segment is obscured.

COMMUNICATING RESULTS

Communicating concerns for a potential PCG diagnosis may be a challenge for optometrists, however it is also important to remember that receiving difficult news can be challenging for parents/caregivers. Although there is no set way to convey such information, a non-alarmist, factual but compassionate approach will help to avoid unnecessary anxiety while still ensuring the parent understands the importance and urgency of following through with the referral. Avoid jargon, reassure the parent that this is the first step in sorting out the child’s eye concerns, and that their child is receiving the best care. If faced with questions regarding prognosis, it may be appropriate to relay that additional clinical information is needed and that many children respond well to treatment.

In almost all cases, an ophthalmologist will need to conduct an examination under general anaesthesia in the operating theatre

TREATMENT

Due to the risks associated with general anaesthesia in babies, surgical treatment usually immediately follows confirmation of PCG diagnosis under the same anaesthesia. Control of IOP is most often achieved with goniotomy and/or trabeculectomy to restore normal aqueous outflow. Success rates of both procedures are reported to be up to 90%. Other surgical procedures, such as trabeculectomy or drainage implant, may be required when IOP is not sufficiently reduced or in more advanced cases. Ciliary body ablation techniques are considered as a last resort.^6,16.21

The age at which diagnosis is made and the timing of treatment has a direct bearing on the visual outcome

Medical IOP lowering therapy alone has a limited role in PCG given the angle anomaly. However, it can play a supportive role before surgery or as an adjuvant treatment postoperatively when surgical outcomes are suboptimal and in cases when surgery is not possible.6 In addition to its provisional efficacy, compliance, and the long-term safety profile, topical IOP lowering drugs can be a concern in babies. Therefore, therapeutic management of PCG is best initiated by the ophthalmologist only.

VISUAL IMPAIRMENT

Vision impairment in PCG is multifactorial. Vision loss can occur as a direct result of glaucomatous neuropathy and/or corneal opacities, however deprivation amblyopia is identified as the leading cause.²² Promptly addressing the underlying aetiology is essential for significantly improved visual outcomes (Table 6). Amblyopia secondary to a sensory tropia is also possible.²³

PROGNOSIS

The age at which diagnosis is made and the timing of treatment has a direct bearing on the visual outcome. PCG present at birth to one month carries the highest risk for vision loss, likely due to a more severe angle anomaly and thus higher IOP. Corneal oedema secondary to IOP elevation in the first three months often results in a poor visual outcome. Unilateral PCG cases tend to have poorer visual outcomes secondary to amblyopia. Photophobia may persist if splits in Descemet’s membrane are severe. Diagnosis between the age of three to 12 months, with prompt treatment, appears to carry the most favourable prognosis.

FOLLOW-UP

Frequent follow-up is required post-surgery to determine the response to treatment and monitor for surgical complications. Thereafter, lifelong follow-up is necessary to monitor IOP, optic nerves, visual development, and risks associated with axial elongation such as retinal detachment. Functional perimetric assessments should be performed when the patient is older. It is also prudent to examine first-degree relatives of confirmed PCG patients, including siblings. Connecting patients and their families to support services and other resources early on, is paramount.

PCG when left untreated results in blindness. Recognising the unique features of PCG is crucial for timely diagnosis and intervention. Treatment extends beyond successful control of IOP and involves promptly addressing uncorrected refractive errors, amblyopia, and other ocular comorbidities. Ongoing optometrical and ophthalmological management is key to care and paramount in achieving optimal visual outcomes.

Anna Delmadoros is Adjunct Lecturer at the School of Optometry, Faculty of Medicine and Health UNSW, and Associate Editor for Clinical and Experimental Optometry. She also serves on advisory panels for Glaucoma Australia and Optometry Australia’s Continuing Professional Development. Her expertise is in ocular disease, therapeutics, and clinical optometry, with over two decades in teaching and education at undergraduate and postgraduate levels in these fields. She has also presented at numerous professional education events.

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