NIHR Signal New tests by a technician in glaucoma clinics could free up specialist appointments

Published on 23 March 2016

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.

New tests by a technician in glaucoma clinics could free up specialist appointments

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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).

Bibliography

American Academy of Ophthalmology. Optic nerve and retinal nerve fiber imaging. In: Eye wiki [internet]. American Academy of Ophthalmology; 2015.

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.

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).

Bibliography

American Academy of Ophthalmology. Optic nerve and retinal nerve fiber imaging. In: Eye wiki [internet]. American Academy of Ophthalmology; 2015.

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.

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)

Published on 1 January 2016

Azuara-Blanco A, Banister K, Boachie C, McMeekin P, Gray J, Burr J, Bourne R, Garway-Heath D, Batterbury M, Hernandez R, McPherson G, Ramsay C, Cook J

Health Technology Assessment , 2016

Background Many glaucoma referrals from the community to hospital eye services are unnecessary. Imaging technologies can potentially be useful to triage this population. Objectives To assess the diagnostic performance and cost-effectiveness of imaging technologies as triage tests for identifying people with glaucoma. Design Within-patient comparative diagnostic accuracy study. Markov economic model comparing the cost-effectiveness of a triage test with usual care. Setting Secondary care. Participants Adults referred from the community to hospital eye services for possible glaucoma. Interventions Heidelberg Retinal Tomography (HRT), including two diagnostic algorithms, glaucoma probability score (HRT-GPS) and Moorfields regression analysis (HRT-MRA); scanning laser polarimetry [glaucoma diagnostics (GDx)]; and optical coherence tomography (OCT). The reference standard was clinical examination by a consultant ophthalmologist with glaucoma expertise including visual field testing and intraocular pressure (IOP) measurement. Main outcome measures (1) Diagnostic performance of imaging, using data from the eye with most severe disease. (2) Composite triage test performance (imaging test, IOP measurement and visual acuity measurement), using data from both eyes, in correctly identifying clinical management decisions, that is ‘discharge’ or ‘do not discharge’. Outcome measures were sensitivity, specificity and incremental cost per quality-adjusted life-year (QALY). Results Data from 943 of 955 participants were included in the analysis. The average age was 60.5 years (standard deviation 13.8 years) and 51.1% were females. Glaucoma was diagnosed by the clinician in at least one eye in 16.8% of participants; 37.9% of participants were discharged after the first visit. Regarding diagnosing glaucoma, HRT-MRA had the highest sensitivity [87.0%, 95% confidence interval (CI) 80.2% to 92.1%] but the lowest specificity (63.9%, 95% CI 60.2% to 67.4%) and GDx had the lowest sensitivity (35.1%, 95% CI 27.0% to 43.8%) but the highest specificity (97.2%, 95% CI 95.6% to 98.3%). HRT-GPS had sensitivity of 81.5% (95% CI 73.9% to 87.6%) and specificity of 67.7% (95% CI 64.2% to 71.2%) and OCT had sensitivity of 76.9% (95% CI 69.2% to 83.4%) and specificity of 78.5% (95% CI 75.4% to 81.4%). Regarding triage accuracy, triage using HRT-GPS had the highest sensitivity (86.0%, 95% CI 82.8% to 88.7%) but the lowest specificity (39.1%, 95% CI 34.0% to 44.5%), GDx had the lowest sensitivity (64.7%, 95% CI 60.7% to 68.7%) but the highest specificity (53.6%, 95% CI 48.2% to 58.9%). Introducing a composite triage station into the referral pathway to identify appropriate referrals was cost-effective. All triage strategies resulted in a cost reduction compared with standard care (consultant-led diagnosis) but with an associated reduction in effectiveness. GDx was the least costly and least effective strategy. OCT and HRT-GPS were not cost-effective. Compared with GDx, the cost per QALY gained for HRT-MRA is £22,904. The cost per QALY gained with current practice is £156,985 compared with HRT-MRA. Large savings could be made by implementing HRT-MRA but some benefit to patients will be forgone. The results were sensitive to the triage costs. Conclusions Automated imaging can be effective to aid glaucoma diagnosis among individuals referred from the community to hospital eye services. A model of care using a triage composite test appears to be cost-effective. Future work There are uncertainties about glaucoma progression under routine care and the cost of providing health care. The acceptability of implementing a triage test needs to be explored. Funding The National Institute for Health Research Health Technology Assessment programme.

Confocal laser scanning ophthalmoscopy (HRT)

The HRT uses confocal laser scanning to measure the optic disc anatomy. There are two main classification tools to relate measurements to normal ranges: (1) HRT-MRA, which requires user input to determine the optic disc boundary, and (2) HRT-GPS, which is fully automated.

Scanning laser polarimetry (GDx)

The GDx scanning laser polarimeter measures the retinal nerve fibre layer (RNFL) thickness surrounding the optic disc. The software automatically provides a measurement termed the nerve fibre indicator.

Optical coherence tomography (OCT)

Spectral domain OCT provides high-resolution, cross-sectional images of the retina. The Spectralis® optical coherence tomograph (Heidelberg Engineering, Heidelberg, Germany) was used in this study.

The ophthalmic team (information from NHS Choices: Glaucoma (2015).

  • An optometrist examines eyes, tests your sight and prescribes and provides glasses and contact lenses. Optometrists are trained to recognise eye defects and eye diseases. Some prescribe treatment for common eye conditions.
  • An ophthalmic medical practitioner (OMP) is a medical doctor who specialises in eye care. They examine the eyes, test sight, diagnose abnormalities and prescribe corrective lenses.
  • An ophthalmologist is a medical doctor who specialises in eye disease and its treatment. They mainly work in hospitals and hospital eye departments.
  • A dispensing optician fits prescriptions for glasses provided by optometrists, OMPs or ophthalmologists. They may also fit contact lenses after having specialist training. A dispensing optician does not examine eyes.

Expert commentary

The study provides interesting findings about the refinement of glaucoma referrals using various diagnostic equipment within secondary care settings. The data on the relative sensitivity of the different equipment, compared with the reference standard of an experienced ophthalmologist, provides useful insights into the comparative benefits of these items. It would be interesting to see how the relative costs / benefits of the equipment considered were influenced by extending the model to reflect that fact that the majority of referrals are made in primary care settings. It would also be interesting to understand how the relative costs might be moderated by the influence of the utility of the different technologies for other eye health diagnostic processes.

Michael Bowen, Director of Research, The College of Optometrists

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