Guidance

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

Updated 27 September 2024

Applies to England

1. Overview

This document provides guidance for local diabetic eye screening (DES) services on the management of individuals in the digital surveillance (DS) with Optical Coherence Tomography (OCT) pathway.

The national DES service specification states that people who need more frequent review, but do not require referral to a hospital eye service (HES) should be referred to DS clinics. It also advises that DS clinics should include OCT for the assessment of maculopathy. Individuals should be referred to HES once they meet, or are on course to meet, treatment criteria for maculopathy or meet the thresholds for R3A or higher risk R2. Services must implement quality assurance (QA) and failsafe measures to maintain patient safety as part of their DS with OCT pathway.

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

2. Screening pathway

Individuals who are graded as having any M1 pathology, including those with R3S or lower risk R2 should be referred to a DS with OCT clinic, except where there is pathology as defined as higher risk M1 or higher risk R2.  DS clinic with OCT should provide both digital fundus photography consistent with national criteria and OCT capture using either spectral domain (SD) or swept source (SS) OCT. Referral in to, and from these, clinics will be counted in the pathway standards.

The OCT scan quality, grade and outcome for the DS with OCT encounter must be recorded within the screening software using the features based grading (FBG) form. This may include a report output from the OCT and the relevant slice of the retina.

For grading, the complete macular area of the OCT must be viewable (currently this may be through separate IT image software) and should be graded by two OCT qualified graders. Services that do not use two level grading for OCT must be able to provide assurance of the quality of the OCT interpretation to the satisfaction of Screening Quality Assurance and Commissioners.

3. Training

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

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

Individuals undertaking OCT grading (ophthalmologists, optometrists and technicians) should be:

• adequately trained in interpreting OCT scans;
• assessed and ‘signed-off’ as competent by the local DES service clinical lead or senior specialty ophthalmologist with medical retinal experience if appropriate; and
• where the grader is performing final outcome grading, should be an active referral outcome grader (ROG) who complies with the associated QA criteria.

Training for OCT interpretation must either be provided locally or by undertaking one of the certificated OCT courses available for Interpretation of Optical Coherence Tomography, providing the clinical lead is assured the content of the course is relevant for the DES programme.

If provided locally, a trainer can be a:

• consultant ophthalmologist, associate specialist, staff grade or specialist registrar who has at least one year’s experience of medical retina clinics and understands and follows national grading criteria for DES; or
• an individual who is experienced with OCT interpretation, 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 fundus images and OCT scans;
• training over several sessions; and
• documented feedback report.

To continue assessing OCTs, the grader should:

• attend regular clinical supervision and continuing professional development (CPD) feedback sessions with the clinical lead or designated deputy;
• grade a minimum of 100 OCT examinations per year of people with diabetes;
• have OCT intergrader agreement reports reviewed regularly and disagreements discussed with clinical supervisor; and
• maintain an auditable record of all clinical supervision sessions and intergrader agreement reports.

Local DES services may have additional eligibility, training and QA criteria for OCT imaging and graders. They should document these additional requirements in local standard operating procedures.

Services 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. Higher Risk Maculopathy

Higher risk M1 cases identified in the routine digital screening (RDS) pathway should be referred directly to Hospital Eye Services (HES) following national referral pathways. This is to ensure there is no delay to treatment by insisting on an OCT being carried out in DES prior to the referral. It may be advisable for the referring grader to add a note in the referral letter to ophthalmology and suggest that this person with diabetes is seen sooner than routine, if appropriate.

Higher risk maculopathy is defined as:

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

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

5. Digital Surveillance with OCT pathway

The DS with OCT pathway describes the pathway DES services must follow when using OCT in digital surveillance clinics.Diabetic Eye Screening Pathway Overviews

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 RXM1.

5.2 Discharges from HES to DS with OCT

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

• R1M1: follow up in DS with OCT in 3 or 6 months (as directed by the discharging clinician)
• R2LM0 or R2LM1: follow up in DS with OCT in 3 or 6 months (as directed by the discharging clinician)
• R3SM1: follow up in DS with OCT 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 in the DS with OCT pathway

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

6. OCT Quality

An OCT scan is adequate if:

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

An OCT scan is inadequate if the OCT quality fails to meet definition of adequate above, including when:

• severe artefacts are present (for example, significant deviations in retinal contour) or the signal strength is so reduced across the scan that major features cannot be identified.

7. OCT Grading Description

The OCT scans should be reviewed in combination with the digital fundus images obtained. When performing grading, the whole macular OCT scan area must be scrolled through and reviewed, not just the central foveal cut. It should also be noted that the definition of ‘1DD from the centre of the fovea’ for OCT is based on the OCT grid shown below and is the area within the middle ring (3mm).

Please see examples:

• OCT examples (https://www.gov.uk/government/publications/diabetic-eye-screening-optical-coherence-tomography-in-surveillance/oct-examples)

7.1 OCT negative

OCT negative is defined as the absence of features required to meet the OCT positive or borderline criteria.

7.2 OCT borderline

OCT borderline is defined as:

• intraretinal cysts within the DES defined macular area with no change in the foveal contour within the macular region; and/or -an area of retinal thickening less than 1-disc area within the DES Programme definition of the macula but more than 1DD from the centre of the fovea providing there are no features which meet the OCT positive criteria.

7.3 OCT positive

OCT positive is defined as intraretinal cysts together with 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 DES Programme definition of the macular.

 

8. OCT Outcomes

Non-DR Features:

• refer to HES for non-DR, if non-DR features meet the criteria set within local protocols and require referral.

OCT Negative Outcome:

• refer to Routine Digital Screening (12-month recall), if R1M0 or R0M0; or
• retain in DS for follow-up, if R3SM0, R2LM0, R1M1, R2LM1 or R3SM1.

OCT Borderline Outcome:

• retain in DS for follow-up.

OCT Positive Outcome:

• refer to HES, if OCT indicates diabetic macular oedema has reached, or is on course to reach treatable levels (exact levels to be defined by local protocols depending on type of OCT machine in use) for example:
  • o   Central Retinal Thickness is of a suitable thickness in microns within the Early Treatment of Diabetic Retinopathy Study (ETDRS) defined central subfield; or
  • o   There is an area of thickening to a suitable degree in microns which is equal to or larger than a disc area within the DES Programme definition of the macular; or
• retain in DS for follow-up if OCT positive but not at threshold for referral to HES.