Guidance

Diabetic eye screening: guidance when adequate images cannot be taken

Updated 27 August 2021

This NHS Diabetic Eye Screening (DES) Programme document provides guidance when images:

• cannot be taken
• are inadequate

Deciding on image quality at the point of capture is within the competencies of a screener and covered in the health screening qualification.

When images cannot be taken

When images cannot be taken, the screener should make a record at the point of screening explaining why. Possible reasons include:

• administration discrepancies
• the individual did not consent
• technical reasons (described in more detail later in this guidance)

If this happens, record an exception to image capture and return the individual to the administration queue for automatic re-invitation as soon as possible.

People who are not able to sit for an image

In situations where the person is not able to sit at the camera:

• a dummy image (for example of the screener’s hand) should be taken
• refer them to the referral outcome grader (ROG) for a decision whether or not to re-screen or exclude

Take notes to inform ROG of the reasons why to aid their decision.

Rules around exclusions can be found in the DES cohort management guidance.

When images can be taken

Deciding on image quality at the point of screening

The screener capturing the images must decide if the images are of sufficient quality at the point of image capture. In cases where the images are not deemed to be of sufficient quality the screener must:

• capture extra images and photograph around the opacity (jig sawing)
• take anterior segment views to show the opacity and the reason for the inadequate images
• use the small pupil setting where appropriate

An adequate image set is one where the area of interest is positioned within the defined limits and has enough clarity for a reliable decision on the individual’s status.

The screener should select if the images captured are adequate or inadequate. The software will allow this decision to be recorded for each eye.

Deciding on image quality at the point of grading

All images (adequate and inadequate) go forward to primary disease grading regardless of image quality.

The grader must select the either adequate or inadequate for the image quality.

All diabetic retinopathy (DR) features must be recorded on the features based grading (FBG) form.

The software will automatically select the worse outcome for each eye.

If the image quality is inadequate for grading, but referable features are present, the referral grade will be automatically selected as the final grade. The software moves the individual onto the referable grade pathway while still recording that the overall image set was inadequate.

The unassessable (U) grade will be automatically selected as the final grade when:

• the image quality is inadequate for grading
• there are no referable features

The software moves the individual onto the U grade pathway.

If the primary grader disagrees with the decision of image quality (adequate or inadequate) taken at image capture, they can record a different image quality decision.

Screeners should attempt to capture extra images (jig sawing) where opacities are present.

An adequate view of the retina can be achieved by combining a series of images. Capturing a far temporal view is often the best way to photograph around a central opacity.

Definition of adequate image quality

The definition of adequate image quality includes:

• 2 nominal 45 degree fields per eye (one fovea centred and one disc centred)

• a combined assessment of field position and image quality for each eye

• only marking images as adequate if the grader is confident the image quality is sufficient

• all grading being performed by qualified staff

An adequate image set is one where the area of interest is positioned within the defined limits. There should be enough clarity for a reliable decision on the grade.

There may be areas of the retina which are not fully visible. The grader should be confident that the image quality is sufficient and the images can be graded as adequate. Primary and secondary graders should make this decision independently.

Combined assessment of field position and image quality

A combined assessment of field position and image quality is described below.

Adequate

Macular image: the centre of fovea is > 2DD from edge of image and the 3rd generation vessels are visible within the macula.

Disc image: the complete optic disc is > 2DD from edge of image and the fine vessels are visible on surface of disc.

Inadequate

Failure to meet definition of adequate as described above.

Grade allocation rules for grading adequate and inadequate images

Adequate images

Follow the standard grading pathway for adequate image sets.

Inadequate image sets

For inadequate images sets, any R0, R1 or R3S features ticked on the FBG form will be recorded in the software. The software will produce a U grade and follow the specified pathway for ungradable images.

Any R2, R3A or M1 features ticked in the FBG form will be recorded in the software. The software will produce the associated referral grade and follow the specified pathway for referable images.

The final grading stage for both these scenarios is referral outcome grade.

Reporting outcomes for image capture exceptions and inadequate images

When no images can be captured for technical reasons

Reasons for it not being possible to capture images include:

• technical failure
• equipment malfunction
• power cut
• broken camera
• broken computer
• operator error

Actions

The screener must record the event in the software. Unreliable cameras or laptops should be reported as per the local policy.

Return the individual to the administration queue. They will be automatically re-invited as soon as possible.

An appropriate letter should be issued to the individual and their GP.

Any reason why an image is inadequate

This would be because both eyes are obscured by media opacity or other issue prevents adequate view of one or both retina.

Actions

The screener must take an anterior shot, record the image quality decision and any further comments in the software to support the ROG decision. The grader records grade as U.

The ROG should determine the outcome, which could be:

• issue another appointment for repeat imaging

• refer to slit lamp biomicroscopy (SLB)

• refer to hospital eye service (HES)

• exclude from screening if the individual is considered unsuitable for further screening or treatment

Issue letter to the individual and their GP.

Individual not able to maintain position

If an individual is not able to maintain their position at the camera, the screener must record the image quality decision and comments in the software to support the ROG decision. The grader must record a U grade on the grading form.

The ROG should determine outcome. This could be to:

• refer to SLB

• refer to HES

• exclude from screening

As described in the exclusion guidance, not all ROG graders are qualified to make a decision to exclude from screening.

The local service should issue an appropriate letter to the individual and their GP. The GP should be asked if they agree with the exclusion. The exclusion process will only be complete if the GP agrees.