Glaucoma: Where Are We Today?

The glaucomas are a collection of progressive optic neuropathies characterised by degeneration of retinal ganglion cells, resulting in optic nerve cupping and visual field defects. They are the leading cause of irreversible vision loss worldwide, and the second leading cause of blindness.¹

Glaucoma is sub-categorised into open and closed angle disease, with primary or secondary aetiology. Secondary causes of glaucoma include ocular conditions (eg. pigment dispersion syndrome, lens related pathology and pseudo-exfoliation), local or systemic inflammation and vascular conditions, and certain medications.² 

In 2020, glaucoma is estimated to effect between 66 million and 80 million people globally, with 11 million people suffering bilateral blindness as a result

EPIDEMIOLOGY

In 2020, glaucoma is estimated to effect between 66 million and 80 million people globally, with 11 million people suffering bilateral blindness as a result.^3-5 The number of people with glaucoma increases annually as the population ages, and by 2040, 112 million people worldwide are predicted to be affected by this disease.⁵ The prevalence of primary open-angle glaucoma is highest in Africa (4.2%), while primary angle closure glaucoma is highest in Asia (1.09%).⁵ 

Locally, the recently published results of the National Eye Health Survey (NEHS) show the prevalence of ‘definite’ glaucoma to be 1.5% in non-Indigenous Australians over the age of 50, and 0.6% in Indigenous Australians over the age of 40.⁶ When ‘definite’ and ‘probable’ cases of glaucoma are combined, the prevalence increases to 3.4% in the non-Indigenous population, and 1.6% in the Indigenous population. The authors hypothesise that genetic factors and/or a lower life expectancy may play a role in the lower prevalence of glaucoma in the Indigenous cohort.

The non-Indigenous Australian prevalence is similar to the global prevalence of 3.5% in 40–80 year olds reported by Tham et al,⁵ and represents an increase from research conducted in the 1990s, estimating a 3.0% prevalence of open angle glaucoma in Australians over 49 years old.⁷ The increase in prevalence over the last two decades is expected, given the progressive ageing of the Australian population.⁸ 

Unfortunately, as the disease may remain visually asymptomatic until pathology is very advanced, many people with glaucoma are unaware of their condition. Studies have shown that in high income countries, approximately 50% of patients with glaucoma have a diagnosis,^6,7,9 and in low-income countries less than 10% of patients with glaucoma may be diagnosed.¹⁰ Living in a rural/remote area increases the risk of being undiagnosed. The National Eye Health Survey results show that only 28% of Indigenous Australians with glaucoma self-reported knowledge of their pathology.⁶

In addition to the quality of life and economic burdens suffered by individual patients with glaucoma in Australia, there is a substantial economic cost to the health care system. By 2025, primary open angle glaucoma (POAG) is estimated to result in direct health system costs of AU$784 million per year. Totals costs (health system costs, indirect costs, and cost of loss of well-being) are predicted to be $4.3 billion annually.¹¹ 

RISK FACTORS FOR GLAUCOMA

There is an expansive body of research on the risk factors for developing glaucoma. Importantly, many of these risk factors can be determined with a comprehensive patient history. Correspondingly, patients at risk may be identified by primary health care providers (GPs, community nurses, allied health providers) with a targeted history, then referred to optometrists and ophthalmologists for more comprehensive assessment.

Clear communication between the optometrist and ophthalmologist is vital in collaborative care arrangements

Elevated or Fluctuating Intraocular Pressure 

Elevated intraocular pressure (IOP) is a well-established, major risk factor for all categories of glaucoma.^12-14 The goldstandard method of IOP measurement is with Goldmann applanation and the upper limit of ‘normal’ IOP is considered to be 21mmHg2. Compelling evidence from the Early Manifest Glaucoma Treatment Trial and Ocular Hypertension Treatment Study analysis indicates that every 1mmHg increase in mean IOP is associated with a 10% increased risk of glaucoma diagnosis and progression.^12,15 

Fluctuation in IOP, both over the 24 hour diurnal period and across multiple visits, has also proven to be a risk factor for glaucoma.^16,17 

Age 

Advancing age is a major risk factor for glaucoma.^7,9 The large body of literature to support this is further supported by analysis of data from the recent NEHS study, which showed non-Indigenous Australians 80 years and older were three times more likely to have glaucoma than those aged 60-69 years.⁶

Ethnicity 

The prevalence of age-adjusted POAG is highest among those of African descent. Racette et al reported prevalence up to six times higher in certain African-American age groups, compared with Caucasian groups.¹⁸ In primary angle closure glaucoma, Asian and Inuit populations have increased prevalence, with reports suggesting an approximate three-fold increase.^19-21

Family History 

Another strong risk factor for open angle glaucoma is having a close relative with a history of POAG. For people with a first degree relative with glaucoma, the prevalence of the disease is three to nine times higher than the general population.^22,23 Wolfs et al²⁴ found the lifetime risk of glaucoma in those with a family history of the disease was 22%, compared with 2.3% in relatives of normal controls.

GA is educating and supporting patients 20 years earlier than they were previously

There is also an increasing knowledge of genetic risk factors for glaucoma. Examples include Myocillin mutations in advanced open angle glaucoma²⁵ and copy number variations in TBK1 in normal tension glaucoma.²² 

Myopia 

Several studies have identified myopia as a risk factor for developing glaucoma.^26-28 In more recent years there has been evidence to suggest an association between the degree of myopia and risk of glaucoma development and progression.^27,28 However, as noted in the meta-analysis conducted by Burr et al,¹⁹ myopia predisposes to several non-glaucomatous field defects and myopic discs are difficult to assess for glaucoma, making the studies in this area prone to selection bias.

Eye Injury 

Despite the relative lack of evidence in the literature, traumatic eye injury has long been acknowledged as a risk factor for glaucoma, acutely or years following the injury.²⁹

Corticosteroid and Other Medications 

The most common cause of medicationinduced secondary glaucoma is longterm use of corticosteroids.³⁰ Steroids administered by any route may precipitate an IOP increase.³¹ In patients with open angle glaucoma, 46–92% were found to have an IOP rise two to four weeks after commencing topical ocular corticosteroids.³² 

A large number of medications may precipitate episodes of acute angle closure, and subsequent glaucoma, including adrenergic agents, anti-cholinergics and sulphonamides.³³ 

Diabetes Mellitus 

The relationship between diabetes and the risk of developing glaucoma remains subject to debate.³⁴ However, a meta-analysis by Zhou et al³⁵ showed that in six out of seven case control studies, and five out of six population studies, there was a significant association between diabetes mellitus and POAG. Furthermore, Burr et al¹⁹ reported that diabetic patients were twice as likely to develop onset open angle glaucoma.

Systemic Hypertension and Hypotension 

The literature is inconclusive on the association between systemic hypertension and open angle glaucoma. The Blue Mountains Eye Study⁷ found a linear increase in IOP as systolic blood pressure increased, and Bonomi et al³⁶ found a positive correlation between systemic blood pressure and IOP, as well as an association with POAG. However, a Japanese crosssectional study³⁷ determined that the relationship between elevated blood pressure and glaucoma is likely secondary to the correlation between hypertension and age.

A number of studies have shown associations between low diastolic pressure, decreased ocular perfusion pressure, and higher prevalence of glaucoma.^36,38,39

Smoking 

Research on the association between smoking and glaucoma is equivocal. A meta-analysis by Bonovas et al⁴⁰ suggests an association between current smokers and developing glaucoma, but not past smokers. Doucette et al³⁴ postulate that smoking (along with other environmental risk factors) may result in earlier onset of glaucoma in those with genetic risk factors.

Migraines and Peripheral Vasospasm 

The evidence for an association between migraines, peripheral vasospasm and glaucoma is limited. However, both the Blue Mountains Eye Study⁷ and the Ocular Hypertension Treatment Trial¹² found peripheral vasospasm and migraine headache to be risk factors for glaucomatous optic neuropathy progression. A case control-study from 1985 also identified an association between migraines, Raynaud’s syndrome and normal tension glaucoma. The Collaborative Normal Tension Glaucoma Study⁴² also found migraine headaches to be a risk factor for progression in normal tension glaucoma.

COLLABORATIVE CARE

Due to the ageing population, the number of Australians living with glaucoma is projected to increase. People with glaucoma should be seen by an eye care professional at least twice a year to ensure that their treatment is adequate and their glaucoma stable. Regular reviews are also an opportunity to check patients are compliant with their treatment. Likewise, people who are at risk of developing glaucoma, known as glaucoma suspects, should also be reviewed on a regular basis.

Royal Australian and New Zealand College of Ophthalmologists (RANZCO) has developed guidelines for the collaborative care of glaucoma patients.⁴³ The goals of collaborative care are patient focused treatment, with patients having access to the most appropriate health-care provider in a timely fashion.

In Australia, optometrists and ophthalmologists can co-manage patients. Optometrists are able to review glaucoma suspects as well as stable glaucoma patients, as identified by an ophthalmologist. The ophthalmologist will also give guidelines to the optometrist for referral back to the ophthalmologist as circumstances change. Clear communication between the optometrist and ophthalmologist is vital in collaborative care arrangements. The ophthalmologist however, remains responsible for all management decisions.

In rural and regional areas of Australia and New Zealand, access to health care is limited. Almost all health professionals are less prevalent in rural areas, with even fewer in remote regions. In Australia, there is an under supply of ophthalmologists in rural and remote regions, which means that ophthalmology services may not be available all the time. Patients may need to wait until an ophthalmologist visits the area or alternatively travel to a regional or metropolitan hospital. Therefore, optometrists in these areas will encounter more ocular conditions and pathology as they will take on the role of primary eye care practitioner. The optometrist in regional and rural areas will often play an important role in educating, treating and managing patients with glaucoma. Collaborative care in this situation is vital to ensure all patients are seen on a regular basis.

Public hospital clinics in metropolitan areas are often stretched to meet the demand of the number of patients with moderate to advanced glaucoma. Consequently, they often have waiting periods for routine appointments that exceed a year. In this situation, the benefit to the patient of collaborative care is obvious. Patients who are glaucoma suspects or who have stable glaucoma can be comanaged by optometrists, allowing patients with complex and advanced glaucoma to remain under the care of ophthalmologists in the hospital system.

GLAUCOMA AUSTRALIA

Glaucoma Australia (GA) was formed in the late 1980s to increase community awareness of the glaucomas as potentially blinding diseases. The organisation also provides information and support for glaucoma patients and their families, reinforcing advice and explanations given by their treating ophthalmologists and improving compliance with treatment. GA also funds research into the glaucomas.

In 2018, GA designed the Glaucoma Australia Patient Centred Referral Pathway, an initiative that has dramatically increased the number of referrals received and the demographic of those referrals.

Whereas prior to 2018, GA would receive approximately 300 referrals per year, today the organisation receives 400 referrals per month – a total of 5,689 referrals since launching the referral pathway. Over half of these referrals are via Oculo and the remainder via the GA website.

Furthermore, prior to 2018, the average patient age was 80–89 years and today the average patient who contacts GA is 60–69 years of age. This means that GA is educating and supporting patients 20 years earlier than they were previously.

This has been a remarkable initiative to connect with people who may have glaucoma and their families, and GA’s reach is set to continue thanks to its high profile support. In late 2019, the Governor- General, His Excellency General the Honourable David Hurley AC DSC (Retd) became a patron of GA. Kirk Pengilly from INXS, who has glaucoma, is an ambassador for the organisation.

Glaucoma Australia’s mission is to “Eliminate Glaucoma Blindness”. By connecting to more people with glaucoma this may become a reality. Visit glaucoma. org.au to find out how you can refer patients on to this sight saving organisation.

Dr Katherine Masselos MBBS (Hons) MPH FRANZCO is an ophthalmologist in Sydney with subspecialty interest in glaucoma and cataract surgery. Dr Masselos has presented at Australian and international ophthalmic meetings and has published widely in peer-reviewed literature. She completed a fellowship in glaucoma surgery at Manchester Royal Eye Hospital, in the United Kingdom. During her fellowship she was an investigator in an international trial of microstents for the treatment of glaucoma. Dr Masselos enjoys teaching and supervises RANZCO registrars at Prince of Wales and Sydney Eye Hospital. She is also a lecturer at the University of NSW. Dr Masselos is a member of the Glaucoma Australia Ophthalmology Committee. 

Dr Samuel Dance MBBS, MS, FRANZCO is an ophthalmologist who practices in Sydney and the Central Coast of New South Wales. He specialises in cataract surgery, glaucoma and (medical) retinal conditions. Dr Dance completed his ophthalmology training at Prince of Wales Hospital in Randwick, before moving to the United Kingdom to gain further sub-speciality experience in complex glaucoma and cataract surgery and in the management of medical conditions of the retina at the Cambridge University and Moorfields Eye Hospital Health Trusts, respectively. He has been a reviewer for the Journal of Glaucoma, lectured at both the University of Sydney, and University of New South Wales, and been an investigator for multiple international clinical trials assessing innovative ocular therapies. He is a member of the Glaucoma Australia Ophthalmology committee and a fellow of the Royal Australian & New Zealand College of Ophthalmologists. 

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