Reorganising glaucoma clinics to include new imaging tests undertaken by technicians appeared to have potential for releasing specialist time compared to usual care. However, the practicalities of adding the tests to current pathways of care in eye clinics will need further assessment.
Four strategies included imaging of the back of the eye plus standard eyesight and pressure tests undertaken by nurses and technicians. These tests were promising when used after referral to a specialist service and may be useful in sorting out who amongst those referred might be at low risk of having glaucoma, and who might not need to see the specialist.
As expected, the tests were not perfect though, missing up to one in seven people who might be at risk of glaucoma. If this is implemented in the NHS, further evaluation of the tests will be needed so that the impact of any delayed or missed diagnoses in minimised.
Why was this study needed?
The study was commissioned to test whether imaging tests performed by a technician, if added to current tests, could make more efficient use of specialist time in hospital eye clinics. Glaucoma is the second most common cause of blindness in the UK. It is a chronic, age-related eye condition in which the optic nerve at the back of the eye is damaged by build-up of fluid pressure in the eye, eventually causing sight loss.
It is important to detect and treat the condition as early as possible, to prevent further sight loss, so opportunistic glaucoma screening is carried out as part of regular sight tests. Referrals to hospital can come from optometrists, who carry out these tests in the community, or from general practitioners. Currently only about 25% of those referred to eye clinics are actually found to have glaucoma.
Imaging technologies are being introduced into glaucoma services but their role in the clinic is unclear. The tests are safe and simple, providing automated classifications that potentially could reduce the need for an examination by a clinician. This study aimed to see whether different triage methods including the new imaging tests, when used in hospital clinics, could identify people with and without glaucoma before they were seen by an eye specialist.
What did this study do?
This NIHR-funded diagnostic study, GATE, compared the accuracy and cost effectiveness of four diagnostic imaging tests, in hospital eye clinics, that did not need to be done by a doctor. It also looked at the usefulness of the tests to triage patients who might not need to see a specialist. All patients in the study were also seen by an eye specialist (the gold standard assessment), for comparison purposes. The imaging tests look at the back of the eye where thinning of tissues helps diagnose glaucoma. HRT-MRA, HRT-GPS, GDx and optical coherence tomography were assessed in this study (see Definitions).
The study included 943 participants, average age 60 years, in five hospital eye clinics who received all of the imaging tests. The two parts to the study were designed to determine:
- a diagnosis of glaucoma (mild, moderate or severe) according to well-defined criteria (diagnosis analysis)
- whether or not the patient would be discharged or should be monitored/treated within hospital eye services (triage analysis).
The researchers made assumptions about costs for the imaging approaches and also assumed that eye specialists would have 100% diagnostic accuracy.
What did it find?
- After assessment by an eye specialist, glaucoma was diagnosed in at least one eye in 16.8% of the study participants (prevalence) and 6.5% of people were found to have glaucoma in both eyes. Overall, 37.9% of the study participants were discharged after the first visit.
- The most sensitive single imaging test (HRT-MA) used alone correctly diagnosed glaucoma in 87% of cases (sensitivity 87.0%, 95% confidence interval (CI) 80.2% to 92.1%). This implies that 13% of people with glaucoma might be missed by use of this test alone (false negatives). This test had the lowest ability to correctly identify those without the disease (specificity 63.9%, 95% CI 60.2% to 67.4%).
- Regarding the test performance of triage tests, the HRT-GPS along with eye pressure and visual testing, was the most accurate test of four. It had the highest sensitivity (86.0%, 95% CI 82.8% to 88.7%) but also the lowest specificity (39.1%, 95% CI 34.0% to 44.5%).
- When the researchers modelled the cost effectiveness of using testing strategies for triage (to decide whether people should be discharged or not) HRT-MA imaging plus measurement of intraocular pressure and visual acuity seemed to be the most cost-effective of the four tested.
What does current guidance say on this issue?
NICE guidance on diagnosis and management of glaucoma was published in 2009. At the time of gathering evidence for this guideline, no suitable research was found comparing imaging technologies to expert clinical assessment for glaucoma diagnosis.
In November 2015, NICE decided that this guideline would be updated, with expected publication date of May 2017.
The current recommendation from the National Screening Committee, part of Public Health England, is that a systematic population screening programme for glaucoma is not recommended.
What are the implications?
If a technician did an imaging test plus an eye pressure test and a nurse performed a visual acuity test to identify those people with or without eye disease, there could be a substantial reduction in demand for ophthalmologists’ time, which could be used for other things. In this study, field testing was undertaken later, for those being seen by an ophthalmologist. However, there are uncertainties in the economic evaluation suggest that if a move from current practice to HRT-MRA testing as triage was implemented, some savings would be expected, but this needs further quantification.. The most cost-effective imaging strategy for this combined screening may include HRT-MRA testing. The researchers say that the costs and cost benefits from their economic modelling analysis should be interpreted with caution. It is as yet uncertain whether implementing an efficient triage glaucoma diagnostic system is possible or acceptable.
Citation and Funding
Azuara-Blanco A, Banister K, Boachie C, et al. Automated imaging technologies for the diagnosis of glaucoma: a comparative diagnostic study for the evaluation of the diagnostic accuracy, performance as triage tests and cost-effectiveness (GATE study). Health Technol Assess. 2016;20(8):1-168.
This project was funded by the National Institute for Health Research Health Technology Assessment programme (project number 09/22/11).
NHS Choices. Glaucoma [internet]. Leeds: NHS Choices; 2014.
NICE. Glaucoma diagnosis and management. CG85.London: National Institute for Health and Care Excellence; 2009.
UK NSC. The UK NSC recommendation on Glaucoma screening in adults [internet]. London: UK National Screening Committee; 2016.
Produced by the University of Southampton and Bazian on behalf of NIHR through the NIHR Dissemination Centre