Mapping evidence on screening for Primary Open Angle Glaucoma (POAG) at primary health care level: A scoping review protocol

1. Study background

Glaucoma is the primary cause of irreversible blindness globally.^1–5 The most common type of glaucoma, affecting 90% of patients, is Primary Open-Angle Glaucoma (POAG).^4,6 Primary open-angle glaucoma is a chronic and progressive neurodegenerative disease of the optic nerve, characterized by thinning of the optic disc and/or retinal nerve fiber layer, accompanied by visual field defects. Other scholars suggest that typical optic nerve changes or visual field defects are adequate for diagnosing glaucoma.^7–9 In this context of POAG, “open” delineates a specific anatomical configuration characterized by an unobstructed anterior chamber angle, easily visualized through gonioscopic lens examination. This configuration is distinctly differentiated from closed or narrow-angle glaucoma, nosologically and therapeutically divergent clinical condition whose comprehensive diagnostic and management strategies extend beyond the interpretive scope of the present view.^10,11 Primary angle glaucoma is usually bilateral, although it can be asymmetric, and typically manifests in mid to late adulthood.^9,12 Despite the association between elevated intraocular pressure (IOP) greater or equal to 21 mmHg and POAG, up to 40% of patients with POAG do not exhibit elevated IOP which can be missed sometimes if clinicians solely rely on tonometry to diagnose POAG.¹¹ It is estimated that 3.5% of adults between the ages of 40 and 80 worldwide have glaucoma.¹³ It is anticipated that 111.8 million people will have glaucoma in 2040 due to the growing number and percentage of elderly individuals in the population.^9,14–17

Noticeably, a large number of cases of primary open-angle glaucoma worldwide remain undiagnosed or poorly managed.^18,19 Because early-stage glaucoma is asymptomatic, well-crafted health promotion programs that stress early detection by raising awareness of the value of routine eye exams can effectively increase older populations’ use of eye care services.^12,20 In most contexts, screening for glaucoma in the general population is currently not thought to be cost-effective.^21–24 Because early detection is crucial for protecting visual function, frequent eye exams are advised for high-risk patients. Lowering intraocular pressure is the only validated and widely recognised method of lowering the risk of glaucoma development.¹ Numerous therapies, such as laser therapy, surgery, therapeutic eye drops, or a combination of these, can lower intraocular pressure.²⁵

International policies support screening for the prevention of blindness, as part of the VISION 2020 initiative.^21,26 However, these policies are not being met.^21–23 Previous policies recommended screenings every 2-3 years and included the following tests: 1. Tonometry (Intraocular pressure measurement) 2. Ophthalmoscopy (Optic nerve head evaluation) 3. Perimetry (Visual field test) 4. Gonioscopy (Angle measurement where the iris meets the cornea) 5. Pachymetry (Corneal thickness measurement) 6. Visual Acuity testing.^5,27 Screening should be conducted at the primary health care level, as it is more accessible and affordable for patients, especially for individuals coming from low-middle income countries.²⁴ There is more evidence of glaucoma being detected during cataract surgeries by ophthalmologists, indicating a gap in detection at the secondary health care level as opposed to the primary health care level. This lack of detection at the primary healthcare level may result in the disease progressing severely, leading to higher healthcare costs and a higher likelihood of vision loss.

This study aims to comprehensively identify the existing literature on screening programs or interventions for primary open-angle glaucoma (POAG) at the primary healthcare level. Additionally, the study aims to outline the characteristics of these screening programs/interventions and emphasize the most successful programs that have been implemented at the primary healthcare level.

We searched the Open Science Framework, the Cochrane Database of Systematic Reviews, and the JBI Evidence Synthesis platform and found no completed, started, or proposed scoping or systematic reviews on screening for primary open-angle glaucoma at the primary healthcare level.

2. Methods

The conduct and design of this review will be guided by Arksey and O’Malley’s (2005) scoping review framework guidelines,²⁸ and Levac et al. (2010) methodological enhancement for conducting a scoping review project.²⁸ According to Arksey and O’Malley’s framework, five stages in projecting a scoping review exist: (1) defining the review question and criteria development for studies inclusion; (2) Study search to address the evaluation question; (3) Selection of studies that meet the criteria for inclusion in the review; (4) Data charting from the studies that meet the criteria for inclusion, and (5) Assemble, summarising, and reporting the results.²⁸ The review results will be reported in accordance with the PRISMA extension for scoping reviews (PRISMA-ScR): checklist and explanation.^29,30 The review protocol was registered with the Open Science Framework and can be accessed by this link https://doi.org/10.17605/OSF.IO/9UDPF.³⁶

The University of KwaZulu Natal’s Biomedical Research Ethical Committee (BREC) granted ethical approval for this study, with reference number BREC/00007182/2024. The Declaration of Helsinki, which governs all research involving humans, is followed in this study. Consent was not required because the study would use publicly available, previously published data.

3. Discussion

Primary open-angle glaucoma (POAG) is a leading cause of blindness, but screening for it at the primary care level remains challenging. While ophthalmoscopic disc photos show high specificity for detecting glaucoma, their sensitivity is lower, suggesting additional testing may be necessary.³¹ National screening programs are currently difficult to justify due to test validity issues, manpower constraints, and resource limitations.³² The progression of visual field deficits in some patients may be delayed due to treatment that lowers intraocular pressure with early POAG, as demonstrated in a Swedish trial (ARR 17%, P=0.007), but the impact on vision-related function remains unclear.³³ Further research is needed to develop improved screening tests and evaluate their cost-effectiveness in primary care settings.^31,34 POAG is rarely diagnosed by primary care clinicians, despite being a significant cause of visual loss among the elderly.³⁵

4. Conclusion

This review will help identify research gaps in primary healthcare POAG screening programs and recommend effective interventions.

Authors’ contributions

Conceptualization PNM., SJN., and ZNXK. Methodology PNM., SJN., and ZNXK. Project Administration PNM. Resources Software PNM., TSSM. Supervision Validation ZNXK. Visualization PNM., SJN., ZNXK., TSSM. Writing – Original PNM. Draft Preparation PNM., ZNXK., TSSM. Writing – Review & Editing PNM., ZNXK., TSSM.

Ethics and concern

Although ethical considerations were not mandatory for this protocol project, ethical clearance was obtained from the Biomedical Research Ethical Committee at the University of KwaZulu Natal (BREC/00007182/2024). Ethical clearance for this manuscript was obtained on July 3rd, 2024. This study adheres to the Declaration of Helsinki’s statement of ethical principles for medical research involving humans.