Imaging the Eye

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Imaging the Eye

• Richard Clark
• Senior Retinal Screener
• NHS Tayside
• August 2007

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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
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Retinal Image Capture - Display - Storage
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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
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Image Field Position

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

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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)

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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

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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

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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 3rd generation
• vessels around the
• fovea must be visible

DRS Clinical Grading Sub-Group (Jan 2006)
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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

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Image Quality (3)

• When is a Technical Failure NOT a Technical
  Failure ?

When there is visible Referable Retinopathy or
Maculopathy
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Technical Failures

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

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Retinal Images (1)

• Dilated Diabetic / Year of Birth 1930

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Retinal Images (2)

• Ethnic origin other than white caucasian
• Vietnamese Indian sub-continent

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Retinal Images (3)

• Dilated - Images recorded after 30 min
• Anterior view required

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Retinal Images (4)

• Dilated Diabetic with Cataract
• Anterior view required

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Anterior Segment (RedEye)

• Required for
• Poor Dilation / Opacity

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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

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Causes of Poor Quality Images

• Small Pupils
• Photophobia or Droopy Eyelids
• Deaf People
• Poor Vision
• Media Opacities
• Mental Health problems

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Retinal Screeners

• How good a Screener are you ?

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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
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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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Whats in an image
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Imaging the Eye

• THE END
• Thank you for participating

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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)