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Glaucoma Learning Zone

Glaucoma overview

Read time: 50 mins
Last updated:9th Jun 2022
Published:9th Jun 2022

Glaucoma is a disease of global concern, with cases expected to rise to 112 million worldwide over the coming decades1,2. Explore our Learning Zone to:

  • Discover the prevalence and burden of glaucoma
  • Learn about the risk factors for glaucoma from an expert
  • Understand why glaucoma is difficult to detect

Prevalence and burden of glaucoma

In this video, Professor Anthony King describes the prevalence of glaucoma and explains why it is difficult to estimate. He also highlights major glaucoma risk factors and the burden of glaucoma on patients, health services and society.

Introduction to glaucoma

Glaucoma, known as the ‘silent thief of sight’, is the principal cause of irreversible blindness and visual disability globally, affecting over 60 million people3, 4

Glaucoma is a complex disease with multiple causes5. It occurs when the optic nerve – the conduit between the eye and the brain – becomes damaged6. It is a common eye condition6 characterised by cupping of the optic nerve head, leading to progressive loss of the visual field. At first, peripheral vision is affected with central visual field being unaffected, detection typically occurring only as the disease progresses4. Left untreated, glaucoma can lead to irreversible visual field loss and blindness7. Chronic glaucoma is often not noticed by the patient as it is usually painless and progresses slowly – it is usually only detected once visual field loss becomes apparent. For these reasons, glaucoma is known as the ‘silent thief of sight’3, 8.

Loss of retinal ganglion cells (RGCs) is the key pathological feature of glaucoma; however, the underlying causes of RGC loss are not yet fully understood4. Increased intraocular pressure (IOP) is characteristic of glaucoma and may contribute to loss of RGCs4, 9. IOP becomes elevated when aqueous humour is overproduced or cannot drain properly through the trabecular meshwork where the iris and cornea meet10. However, only around 50% of glaucoma cases exhibit IOP above reference values2, 9. Further, cases of ‘normotensive glaucoma’ have rapidly increased in recent years, with these patients having a higher likelihood of being underdiagnosed2, 9.

Glaucoma comprises two major types, open angle and closed angle. A third type, childhood glaucoma, also exists. Differentiation between open angle and angle closure depends on the appearance of the iridocorneal angle through which aqueous humour drains from the eye – that is, the drainage angle formed by the iris and cornea4, 10.

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Risk factors for glaucoma

Within their lifetime, over 10% of people with glaucoma experience serious visual field loss or become blind in both eyes2

Left untreated, glaucoma can lead to moderate-to-severe vision loss. This highlights the need to be aware of the risk factors for glaucoma, so that people at higher risk can be screened, diagnosed and treated as early as possible, early detection being vital to prevention of disease progression24 and irreversible vision loss. Figure 2 illustrates the major risk factors for the development of open angle glaucoma, the most common form of glaucoma2.


Figure 2. The major risk factors for development of open angle glaucoma2. IOP, intraocular pressure.

Table 3 outlines the risk factors for the more common forms of glaucoma. Of all risk factors, intraocular pressure is the only risk factor known to be modifiable28. Risk factors for secondary subtypes have been excluded from the table, as the risks vary depending on the underlying cause.

Table 3. Risk factors for common forms of glaucoma (Adapted2). BP, blood pressure; CCT, central corneal thickness; IOP, intraocular pressure. *Thinner CCT: not an independent prognostic risk factor for onset/progression of open angle glaucoma in univariate analyses.

Type Risk factors
Primary open angle glaucoma

· Higher IOP

· Older age

· Race/ethnicity: highest prevalence in people of Black race

· First-degree relative with confirmed open angle glaucoma

· Moderate-to-high myopia

· Low diastolic BP

· Thinner CCT*

· Higher IOP

· Older age

· Presence of disc haemorrhages

· Thinner CCT*
Primary angle closure glaucoma

· Older age

· Race/ethnicity: higher prevalence in South and East Asians

· Family history

· Female sex

· Hypermetropia

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Signs and symptoms of glaucoma

Glaucoma symptoms are almost undetectable in the early stages – even once the disease process is underway and nerve fibres have already been damaged3, 9

Early detection of glaucoma is key to early treatment and the prevention of further loss of visual function4.

The signs and symptoms of glaucoma vary depending on the type and stage of the disease. Below are the common signs and symptoms of glaucoma.

Open angle glaucoma symptoms

In the early stages, there are no obvious symptoms of open angle glaucoma. Blind spots, also known as scotomas, usually develop in the peripheral vision although central visual field is affected in some individuals as the disease progresses. Often, changes to vision generally go unnoticed until substantial damage has already occurred and may be masked by a good visual field in the fellow eye6, 8, 10, 28 .

Secondary open angle glaucoma

Being a heterogenous group of conditions, symptoms will vary depending on the underlying cause, although raised IOP is the leading cause2. The signs and symptoms are generally similar although in cases of pseudoexfoliation and pigment dispersion syndrome, specific changes will be noted in the anterior chamber on examination29.

Normal tension glaucoma symptoms

Intraocular pressure is within normal ranges, but signs of glaucoma are present, such as optic nerve damage and blind spots in the field of vision8.

Angle closure glaucoma symptoms

Most commonly, people with angle closure glaucoma are asymptomatic. Sub-acute episodes of increased IOP due to angle closure may occur in some patients and can result in symptoms including blurred vision, haloes, pain and redness. However, the sensitivity and specificity of these symptoms as a means of identifying angle closure is very low2. Given that acute angle closure glaucoma is a medical emergency, it is important that if symptoms develop suddenly – namely red eye, nausea, intense eye pain or blurry vision – the patient seeks immediate treatment. Left untreated, acute angle closure glaucoma can lead to blindness within days6, 12.

Secondary angle closure glaucoma

The clinical signs of secondary angle closure glaucoma vary, depending on the underlying cause2.

Progression of disease

In glaucoma, visual field loss usually begins in the periphery, advancing towards central fixation during disease progression28. However, central loss may be experienced earlier in the disease course28. Typically, rates of glaucoma disease progression are evaluated by measuring structural or functional changes to the optic nerve30. When part of the optic nerve head or retinal nerve fibre layer (RNFL) are affected by structural damage, functional loss is often observed in the corresponding visual field location on perimetry28.

Event analyses compare baseline to follow-up measurements, indicating whether the measurement has worsened, and trend analyses determine the rate of progression by using serial measurements. Trend analyses supplements event analyses in that it helps the clinician understand the velocity of vision loss, and whether this may impact the patient’s vision-related quality of life30.

Using standard automated perimetry for visual field testing is the gold standard for measuring glaucoma progression, despite being patient-dependent and carrying high test-retest variability. Other tests that are used for qualitative and quantitative assessment of rate of structural change include spectral domain and swept-source optical coherence tomography30.

Comparison of sequential perimetry results can indicate whether increases in visual field loss have occurred, which can help inform whether further IOP-lowering treatments may be required28. Disease progression and the need for further IOP-lowering treatment may also be indicated when optical nerve head cupping has expanded, or when increased thinning of RNFL tissue on sequential optical coherence tomography (OCT) tests has been observed28.

One example of a functional tool used to detect visual loss is the Amsler grid (also known as the Amsler chart). It is a simple and rapid qualitative test commonly used for people at risk of macula degeneration. It helps identify and locate defects in the central field of vision: specifically, in the central 10 degrees around a fixation point31, 32.

Figure 3 illustrates how the Amsler grid appears when viewed by a person with normal central vision or with central visual field abnormalities associated with macula degeneration.

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