imaging the eye richard clark senior retinal screener nhs tayside august 2007

Imaging the Eye Imaging the Eye

Richard Clark

Senior Retinal Screener

NHS Tayside

August 2007

Diabetic Retinopathy Screening Programme

Objectives

Primary Objective The detection of referable (potentially sight-threatening) retinopathy so that it can be treated

Secondary Objective The detection of lesser degrees of diabetic retinopathy

Retinal Image Capture - Display - Storage

Scottish DRS Programme Image capture size/settings

Image size must be a maximum of 2Mb (preferably 1.5Mb)

This is to ensure that the images are easily available to graders as local network bandwidth will not be able to cope with large amounts of big images being transferred to and from the National DRS database or local area Staging server

Image Field Position

There are three components to the field Position:

1. Field of View

2. Field Position

3. Number of Fields

Field of View

The recommended field of view is:

A minimum of 45 degrees horizontally

and

A minimum of 40 degrees vertically

This is commonly known as the 45 degree Field

of View (standard setting on fundus cameras)

Field Position

The recommended field position in Scotland:

Disc/Macular field positioned so that the optic disk and fovea

are horizontally displayed on the central meridian of the field of view

The whole of the optic disk is displayed with a thin rim of retina

The fovea is at least 2 x DD from the edge of the retina

Number of Fields

A single Disk/Macular field image for each eye

Additional images (based on the Disk/Macular field) may be required when:

a. A lesion (Diabetic or Non-Diabetic) is close to the edge of the field

b. To provide a better view of significant Retinopathy/Maculopathy

c. If an artefact is obscuring an area of interest

Image Quality (1)

a. The entire optic diskmust be displayedb. The fovea must be at least 2 x DD from edgec. The 3rd generation vessels around the fovea must be visible

DRS Clinical Grading Sub-Group (Jan 2006)

Image Quality (2)

1 (Best) - Nerve fibre layer visible 2 – Nerve fibre layer not visible 3 – Small vessels blurred 4 – Major arcade vessels just blurred 5 (Worst) – Significant blurring of major

arcade vessels in more than 1/3 of image in the absence of visible referable retinopathy

Image Quality (3)

When is a Technical Failure NOT a Technical Failure ?

When there is visible Referable Retinopathy or Maculopathy

Technical Failures

How many Technical Failures are expected:

Measured failure rate from trials is 3.5%

Predicted failure rate is less than 5%

Retinal Images (1)

Dilated – Diabetic / Year of Birth 1930

Retinal Images (2)

Ethnic origin other than white caucasianVietnamese Indian sub-continent

Retinal Images (3)

Dilated - Images recorded after 30 min Anterior view required

Retinal Images (4)

Dilated – Diabetic with Cataract Anterior view required

Anterior Segment (RedEye)

Required for Poor Dilation / Opacity

Anterior Segment (RedEye)

Patient face away from camera Pull out lens diopter Enable fundus view Line up view Focus on pupil margin/lens Record image

Causes of Poor Quality Images

Small Pupils

Photophobia or Droopy Eyelids

Deaf People

Poor Vision

Media Opacities

Mental Health problems

Retinal Screeners

How good a Screener are you ?

Quality Assurance

The images from a minimum of 500randomly selected patients (all if less than 500), not otherwise referred to a thirdlevel grader are checked for:

Failure to note that an image is of such low quality that no screening decision is feasible

Recommended Reading

Health Technology Report 1 – Organisation of Services for DRS (2002)

DRSS in Scotland – Recommendations for Implementation (June 2003)

DRSS in Scotland – A Training Handbook (July 2003)

Clinical Standards for DRS – (March 2004)DRS Clinical Grading Sub-Group – Image

Quality Definition (Jan 2006)

Whats in an image

Imaging the Eye

THE END Thank you for participating

Recommended Reading

Health Technology Report 1 – Organisation of Services for DRS (2002)

DRSS in Scotland – Recommendations for Implementation (June 2003)

DRSS in Scotland – A Training Handbook (July 2003)

Clinical Standards for DRS – (March 2004)DRS Clinical Grading Sub-Group – Image

Quality Definition (Jan 2006)