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Imaging the Eye Richard Clark Senior Retinal Screener NHS Tayside August 2007.

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Presentation on theme: "Imaging the Eye Richard Clark Senior Retinal Screener NHS Tayside August 2007."— Presentation transcript:

1 Imaging the Eye Richard Clark Senior Retinal Screener NHS Tayside August 2007

2 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

3 Retinal Image Capture - Display - Storage

4 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

5 Image Field Position There are three components to the field Position: 1. Field of View 2. Field Position 3. Number of Fields

6 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)

7 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

8 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

9 Image Quality (1) a. The entire optic disk must be displayed b. The fovea must be at least 2 x DD from edge c. The 3 rd generation vessels around the fovea must be visible DRS Clinical Grading Sub-Group (Jan 2006)

10 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

11 Image Quality (3) When is a Technical Failure NOT a Technical Failure ? When there is visible Referable Retinopathy or Maculopathy

12 Technical Failures How many Technical Failures are expected: Measured failure rate from trials is 3.5% Predicted failure rate is less than 5%

13 Retinal Images (1) Dilated – Diabetic / Year of Birth 1930

14 Retinal Images (2) Ethnic origin other than white caucasian Vietnamese Indian sub-continent

15 Retinal Images (3) Dilated - Images recorded after 30 min Anterior view required

16 Retinal Images (4) Dilated – Diabetic with Cataract Anterior view required

17 Anterior Segment (RedEye) Required for Poor Dilation / Opacity

18 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

19 Causes of Poor Quality Images Small Pupils Photophobia or Droopy Eyelids Deaf People Poor Vision Media Opacities Mental Health problems

20 Retinal Screeners How good a Screener are you ?

21 Quality Assurance The images from a minimum of 500 randomly selected patients (all if less than 500), not otherwise referred to a third level grader are checked for: Failure to note that an image is of such low quality that no screening decision is feasible

22 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)

23 Whats in an image

24 Imaging the Eye THE END Thank you for participating

25 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)


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