Guidance

Optical coherence tomography (OCT) in diabetic eye screening (DES) surveillance clinics

Published 8 July 2020

1. Overview

This document provides consistent best practice guidance for local diabetic eye screening (DES) services on the management of diabetic maculopathy in digital surveillance (DS) clinics using optical coherence tomography (OCT).

The national service specification states that people who need more frequent review but do not require referral to a hospital eye service (HES) can be referred to DS clinics. It also advises that DS clinics may link to OCT for the assessment of maculopathy.

The use of OCT is not currently included in NHS England commissioned DES services. Any provision of OCT assessments must be commissioned separately. The commissioning of OCT services should involve commissioners, clinical care groups, general practice, HES and local screening providers.

Providers must implement additional quality assurance (QA) and failsafe measures to maintain patient safety alongside existing failsafe arrangements.

The clinical lead is responsible for the clinical governance of the OCT pathway. A consultant diabetologist clinical lead must appoint a consultant or senior specialty ophthalmologist with medical retina experience to provide dedicated support to the service.

A cost effectiveness study for the use of OCT assessment in screening demonstrated that it is cost effective to use OCT in DS for maculopathy follow-up.

2. Screening pathway

Low risk maculopathy can be followed up in digital surveillance with an OCT. High risk maculopathy and all R2M1 and R3AM1 grades must be referred to HES and follow the national referral pathway.

DS clinics with OCT should provide both digital fundus photography consistent with national criteria and the additional OCT capture using either spectral domain (SD) or swept source (SS) OCT. Referral into and from these clinics will be counted in the pathway standards.

The OCT scan quality, grade and outcome for the DS encounter must be recorded within the screening software using the features based grading (FBG) form. This may include a report output from the OCT of the relevant slice of the retina. The OCT grader must be able to escalate the scan within the pathway for additional grading or a second opinion.

3. Training

The clinical lead is responsible for the clinical governance of the OCT pathway and ensuring the quality standard is met for DS.

Individuals performing OCT imaging must be adequately trained in obtaining appropriate quality OCT images.

OCT graders (ophthalmologists, optometrists and technicians) should be:

• adequately trained in assessing OCT scans
• an active referral outcome grader (ROG) who complies with the associated QA criteria
• assessed and ‘signed-off’ as competent by the local DES provider clinical lead

There must be local training to make sure all OCT graders are competent in interpreting and grading OCT scans for diabetic retinopathy and incidental findings. A trainer can be a:

• consultant ophthalmologist, associate specialist, staff grade or specialist registrar year III (or higher) who has at least one year’s experience of medical retina clinics and understands and follows national grading criteria for DES
• hospital clinical optometrist or an experienced OCT examiner who has a minimum of 2 years’ experience working in medical retina clinics, is approved by the clinical lead and understands and follows national grading criteria for DES

3.1 Formal assessment

The clinical lead must complete an assessment of competence before the grader can undertake unsupervised OCT grading.

This should include:

• a formal assessment of 50 individual OCT scans as a minimum
• identification of all diabetic retinopathy and maculopathy levels
• FBG of both digital photographic images and OCT scans
• training over several sessions
• a documented feedback report

To continue assessing OCTs, the grader should:

• attend an annual continuing professional development (CPD) feedback session with the clinical lead
• grade a minimum number of OCT examinations per year from 100 people with diabetes
• perform peer-reviewed grading of diabetic retinopathy using OCT on at least 20 people with diabetes and with the assessor once every 3 years
• maintain an auditable record of all training and accreditation activity

Local DES providers may have additional eligibility, training and QA criteria for OCT imaging and graders. They should document these additional requirements within local standard operating procedures. Providers should maintain accurate and up to date records of accredited and trainee OCT graders.

They should document all training and assessments within an appropriate training record that can be updated and accessed by the OCT grader, clinical lead and appropriate line management.

4. Definitions and outcomes

High risk maculopathy is defined as:

• macular exudation (circinate) greater than 1/2 disc area and
• within 1 DD of the fovea and
• where there is a drop in visual acuity in this eye to ≤ 6/12

High risk M1 cases identified in the routine digital screening (RDS) pathway should be referred directly to HES following national referral pathways. The referring grader can add a note in the referral letter to ophthalmology and suggest that this person with diabetes is seen sooner if appropriate.

Low risk maculopathy is defined as all maculopathy cases that do not meet the high-risk definition above.

5. OCT pathway

The OCT in surveillance pathway, describes the pathway DES providers must follow if they use OCT in digital surveillance clinics.

5.1 Absence of surrogate markers

Please note that if there are no M1 surrogate markers seen on the retinal image but the OCT is borderline or positive due to diabetic maculopathy, the final outcome grade must be R1M1.

5.2 Discharges from HES to OCT DS

HES can discharge stable treated or untreated maculopathy back to the DS pathway for future closer monitoring.

• R1M1: follow up in OCT digital surveillance in 3 or 6 months (as directed by the discharging clinician)
• R3SM1: follow up in OCT digital surveillance in 3 or 6 months (as directed by the discharging clinician) or in 3 months if benchmark images are not provided

5.3 Progression to R2 or R3A within the OCT DS pathway

Where referable retinopathy R2 or R3A is identified within the OCT DS pathway, the ROG must follow national guidance for referring and managing these individuals.

6. OCT quality

OCT is adequate if:

• artefacts are not present and signal strength appears optimal for interpretation of the image set
• artefacts are present or signal strength is reduced, but there is still enough intensity to distinguish major features across the entire scan
• the grader is confident the quality of the OCT scan is sufficient

OCT is inadequate if:

• severe artefacts are present (for example, significant deviations in retinal contour) or the signal strength is so reduced across the scan that you cannot identify major features
• the OCT quality fails to meet definition of adequate above

7. OCT grading and outcomes

The OCT images should be reviewed in combination with the digital retinal images obtained. The whole macular OCT scan area must be scrolled through and reviewed, not just the central foveal cut.

7.1 OCT negative

OCT negative is the absence of OCT positive or borderline criteria.

Outcome: refer to annual RDS (R1M0) or DS follow-up (R3SM0 and R1M1).

7.2 OCT borderline

OCT borderline is:

• intraretinal cysts with no change in the foveal contour
• an area of retinal thickening less than 1-disc area within the NHS Diabetic Eye Screening Programme definition of the macula

Outcome: refer to DS (with OCT) follow-up.

7.3 OCT positive

OCT positive is intraretinal cysts and one or more of:

• a change in the foveal contour
• an area of retinal thickening greater than 1/2-disc area, the edge of which is within 1 DD of the central fovea
• an area of retinal thickening greater than 1-disc area within the NHS Diabetic Eye Screening Programme definition of the macula

Outcome: refer to HES (unless extenuating circumstances requested by clinical lead).

Please see:

• OCT examples
• pathway diagram for screen positive maculopathy with R1M1 or R3SM1 when OCT in a digital surveillance clinic

Please note that if there are no M1 surrogate markers seen on the retinal image but the OCT is borderline or positive due to diabetic maculopathy then the grade must revert to R1M1.