Efficiency of Eye Movements in Low Vision Patients

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Efficiency of Eye Movements in Low Vision Patients

• Laura Renninger,
• Preeti Verghese Donald Fletcher

The Smith-Kettlewell Eye Research Institute San
Francisco, CA
OSA - Fall Vision Meeting
September 16-19, 2007
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A case study of two patients
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Observation
Two low vision patients with similar visual field
loss and decrease in visual acuity may exhibit
very different functional skills. Why is one
patient better able to cope with their vision
loss than another?
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HYPOTHESIS
Functional differences between patients may be
due to the efficiency of their eye movement
behavior.
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Experimental Methods

• Shape study and matching task
• Long duration (3sec-5sec),
• Large comparison figures (12.5deg)
• SR Research Eyelink 1000
• Video-based eye tracking, comfortable for patient
• Ring calibration stimulus
• Ring size can be adjusted to get stable target
  fixation
• Register microperimetry eye position data

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Shape Matching Task
Shape is 25 deg, presented at an eccentricity of
20 deg on a screen that subtends 40 deg of visual
angle.
Renninger, et. al. Journal of Vision 2007
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Patients select the shape that best matches the
one in the previous interval. Comparison shapes
were shown side by side and subtended
12.5deg. The difference between shapes was
adjusted to be much larger for low vision
patients, making the matching task easier.
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Eye movement statistics for normally-sighted
observers, similar task
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Eye Movement Statistics
The good scanner makes significantly shorter
saccades.
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Eye Movement Statistics
The good scanner holds fixations for a shorter
duration.
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Computing Visual Information
Renninger, Verghese Coughlan Journal of Vision
2007
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Scanning Efficiency
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Missing Information?

• Issue
• Patients will not gain new information about
  parts of the stimulus that fall within their
  scotoma
• Solution
• Model visual field loss using microperimetry data
  collected with a scanning laser ophthalmoscope
• For each fixation, only update knowledge using
  edges that fall outside of the scotoma

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Scotoma Estimation
LD right eye
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Scotoma Estimation
RJ right eye
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Efficiency of Fixation Placement
The computation is relative to each patients
visual field loss.
The good scanner collects more information with
each fixation.
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Discussion
When scotoma profile and visual acuity are
similar, the difference between good and poor
visual function may be attributed to eye scanning
behavior. This study provides the first
quantitative data in support of the hypothesis
that scanning strategies contribute to the
functional outcome of maculopathy patients.
Teaching efficient strategies to poor
scanners may be a viable rehabilitation approach.
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CONCLUSION
Patients may be better able to cope with their
vision loss by making efficient eye movements.
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Acknowledgements

• COLLABORATORS
• Donald Fletcher
• Preeti Verghese
• James Coughlan
• FUNDING SOURCES
• Pacific Vision Foundation
• NIH / NSF Collaborative Research in Computational
  Neuroscience