Glaucoma in Rural Australia: Good News and Risk Factors

How ‘bad’ is a patient’s glaucoma by the time they are diagnosed by an ophthalmologist? Which patients are presenting late? And what are the risk factors for presenting late?

These were the questions we set out to answer using a retrospective review of patient records at the Port Macquarie Eye Centre. We reviewed our patients’ records in the Fight Glaucoma Blindness! registry to identify all patients newly diagnosed with glaucoma at this clinic in 2020 and 2021.

Associations with glaucoma severity at presentation, measured with the visual field index (VFI), were analysed using a beta-regression model. This Severity at 1st Presentation (S1P) study was the first of its kind in an Australian population and has recently been published in Clinical and Experimental Optometry.¹

Given that the degree of visual field loss at the time of diagnosis strongly influences the rate of disease progression and risk of blindness,^2,3 glaucoma severity at presentation constitutes a valuable proxy measure of a healthcare system’s effectiveness, in terms of detection and referral efficiency.

In rural areas, such as Port Macquarie, patients depend on efficient and effective triage and referral by optometrists and other primary care providers to enable timely initiation of treatment and thereby maximally curtail disease progression.

Associations between severity at presentation and demographic factors can also be used to identify and target at-risk populations and compare efficacy of different healthcare systems.

… glaucoma severity at presentation constitutes a valuable proxy measure of a healthcare system’s effectiveness, in terms of detection and referral efficiency

A Specific Cohort

Port Macquarie is an idyllic town on the New South Wales Mid North Coast with a population of ~80,000.⁴ Compared to NSW state averages, in Port Macquarie the population is older, has a greater proportion of Caucasian residents and also Aboriginal and Torres Strait Islander residents, and reports a lower average household income.4 Port Macquarie also serves as a regional hub, servicing a large catchment of smaller surrounding rural areas (Figure 1). The Port Macquarie Eye Centre comprises five of six full-time and two of three part-time ophthalmologists servicing the Port Macquarie district, including the only two glaucoma subspecialists.

To ensure we captured the correct cohort for this review, we excluded patients who opted out of the Fight Glaucoma Blindness! registry, those with a previous diagnosis of glaucoma by an ophthalmologist or optometrist, those previously deemed glaucoma suspects by an ophthalmologist, those with no visual fields or unreliable visual fields, and those with severe retinal pathology likely to confound their visual fields.

In total, 3,538 new patients were seen at the Port Macquarie Eye Centre from 2020–2021, including 110 new glaucoma diagnoses (3.1% of new patients seen at this clinic). Of these, 89 were referred for suspicion of glaucoma and 21 were referred for other reasons, with glaucoma diagnosed incidentally on initial examination. Most cases were referred by optometrists (101 cases), with a smaller number referred by general practitioners (five cases), other ophthalmologists (three cases; for reasons other than glaucoma), and emergency physicians (one case). The Fight Glaucoma Blindness! registry records of 95 patients met the inclusion criteria.

The cohort was 50.5% male, had a mean age of 70, a mean intraocular pressure (IOP) at diagnosis of 22.5 mmHg, and 75.8% of cases were primary open angle glaucoma.

The Findings

The VFIs of the cohort revealed that glaucoma was diagnosed relatively early in this population, with a median VFI of 94.5% at presentation and 71.6% of patients presenting with a VFI greater than or equal to 90%. This would suggest a well-functioning primary care referral system. Despite the relatively greater scarcity of service providers and resources in this rural setting compared to a metropolitan region, we found that glaucoma patients here are still being referred promptly.

The findings also suggested that most cases in this population would be amenable to treatment with a good visual prognosis, given their early stage at diagnosis. However, there was still a group of very late presenters – six patients (6.3% of the cohort) – who presented with a VFI below 50%. Of these, 83% had primary open angle glaucoma and 50% were over 80, but it was otherwise difficult to comment on any factors unique to these latest of late presenters.

However, we were able to show that older age (p <0.001), higher initial IOP (p = 0.026), and poorer visual acuity (p = 0.041) were strongly associated with glaucoma severity at presentation (Table 1), while other factors were not found to be significant in this study. Importantly, we found no evidence for an association between remoteness (measured using the Modified Monash Model) and VFI (p = 0.260), with no significant difference between remoteness levels observed. This suggests that the Port Macquarie structure of rural service provision, with an ophthalmic practice in a large rural town (Modified Monash 3) servicing medium and small rural towns (Modified Monash 4–5), does not disadvantage patients’ timeliness of diagnosis.

Thus, older age, higher initial IOP, and poorer visual acuity (as well as male sex and glaucoma type) are significant predictors of glaucoma severity at presentation and represent key factors for primary care providers to be aware of when considering glaucoma referrals. In particular, the association with age represents a key target for public health screening strategies, underscoring the importance of frequent comprehensive eye examinations in older patients. Age has been previously correlated with severity at presentation.^2,5-8 This is likely attributable to declining access to healthcare due to age-associated mobility issues, social isolation, relocation to aged care, increasing rates of cognitive impairment, and competing health priorities.^5,8,9 In their seminal work, Fraser et al. proposed that late presentation is a function of the rapidity of visual field deterioration and the frequency of eye examinations.⁵ The relationship between age and severity at presentation represents a combination of these factors, but the frequency of eye checks is the key modifiable factor in this relationship. Accordingly, our findings suggest that more frequent comprehensive eye examinations in older patients have the potential to reduce late glaucoma presentation.

Table 1. Estimates of associations between predictors and visual field index (VFI) using multivariable beta regression.

Limitations and Key Strengths of Study

Limitations include the absence of other possible predictors of severity, chiefly socioeconomic status, which is an established predictor of late presentation and of access to healthcare.^6,10,11 Other potential predictors include insurance status, educational attainment, employment status, knowledge of glaucoma, time since last ophthalmic examination, referral source, and indication, Aboriginal and Torres Strait Islander status, and cognitive impairment. The absence of these predictors in our model does introduce the possibility of confounding bias. The study design also meant it could not capture patients who were referred but never attended an appointment, though this would be a particularly interesting group in the context of severity at presentation. Finally, prospective studies are required to establish causal links between the risk factors identified and further replication in other Australian populations is also needed.

However, key strengths of this study include its novel use of the Fight Glaucoma Blindness! registry, use of a clinically applicable severity measure (VFI), and that it is both the first to investigate predictors of severity at presentation in an Australian population and the first to focus on patients in a regional setting. We have shown that glaucoma is diagnosed relatively early in this population, but that there are several key predictive factors for late presentation with glaucoma, which clinicians should be aware of. These represent key targets for population strategies to optimise early detection and timely referral for new glaucoma patients, and thus maximise preservation of vision.

Dr Zayn Al-Timimi is a recently graduated junior doctor interning at Coffs Harbour Health Campus in 2024. He has a keen interest in ophthalmology and is also undertaking a Masters by Research from the University of New South Wales, with a thesis entitled, ‘What matters to patients when choosing glaucoma surgery?’.

Dr Hamish Dunn is an ophthalmologist with subspecialty training in glaucoma and oculoplastics. He has worked with Sight for All in Cambodia and Laos and with UNICEF in Guyana, South America prior to medicine. His PhD research is on developing optimised ways for non-experts to examine the fundus, and he is actively involved in clinical glaucoma research. He has clinical teaching and research affiliations with Westmead Hospital, the University of Sydney, and University of NSW.

References

1. Al-Timimi Z, Campbell A, Dunn H, et al. Glaucoma severity at first presentation to an ophthalmologist and risk factors for late presentation in rural Australia: the S1P study. Clin Exp Optom. 2024;6:1-8. doi: 10.1080/08164622.2024.2344835.
2. Deva NC, Insull E, Gamble G, Danesh-Meyer HV. Risk factors for first presentation of glaucoma with significant visual field loss. Clin Exp Ophthalmol. 2008;36(3): 217-221. doi: 10.1111/j.1442-9071.2008.01716.x.
3. Lee JM, Caprioli J, Coleman AL, et al. Baseline prognostic factors predict rapid visual field deterioration in glaucoma. Invest Ophthalmol Vis. Sci. 2014;55(4):2228–2236. doi: 10.1167/iovs.13-12261.
4. Australian Bureau of Statistics, Port Macquarie: 2021 census all persons quickstats. available at: abs.gov.au/census/find-census-data/quickstats/2021/SED10068 [accessed Dec 2024].
5. Fraser S, Bunce C, Wormald R. Retrospective analysis of risk factors for late presentation of chronic glaucoma. Br J Ophthalmol. 1999;83: 24-28. doi: 10.1136/bjo.83.1.24.
6. Ng WS, Agarwal PK, Azuara-Blanco A, et al. The effect of socio-economic deprivation on severity of glaucoma at presentation. Br J Ophthalmol. 2010;94:85-87. doi: 10.1136/bjo.2008.153312.
7. Abdull MM, Gilbert CC, Evans J. Primary open angle glaucoma in northern Nigeria: stage at presentation and acceptance of treatment. BMC Ophthalmol. 2015;15:111. doi: 10.1186/s12886-015-0097-9.
8. Belete BK, Assefa NL, Ayele FA, et al. Determinants for late presentation of glaucoma among adult glaucomatous patients in University of Gondar Comprehensive Specialized Hospital. Case-control study. PLoS One 17, 2022 Apr 29;17(4): e0267582. doi: 10.1371/journal.pone.0267582.
9. Odayappan A, Kavitha S, Venkatesh R, at al. Assessment of reasons for presentation in new primary glaucoma patients and identification of risk factors for late presentation. Ophthalmol Glaucoma 4, 382–389 (2021). doi: 10.1016/j.ogla.2020.11.007.
10. Gupta V, Srivastava RM, Singh D, et al. Determinants of severity at presentation among young patients with early onset glaucoma. Indian J Ophthalmol. 2013 Oct;61(10):546-51. doi: 10.4103/0301-4738.121064.
11. Buys YM, Jin YP; Canadian Glaucoma Risk Factor Study Group. Socioeconomic status as a risk factor for late presentation of glaucoma in Canada. Can J Ophthalmol. 2013;48:83-87. doi: 10.1016/j.jcjo.2012.10.003.