Horopter

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Horopter
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Horopter

• Definition The locus of all points in visual
  space that are imaged on corresponding points in
  each eye when the eyes are converged at fixed
  location. This is called the theoretical point
  horopter.

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Horopter

• It is 3 dimensional
• Horizontal component
• Vertical component
• We will mainly deal with the horizontal horopter.

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Geometrical Horopter

• Vieth Muller Circle This is the geometric
  representation of the corresponding assuming
  perfect optics of the eye

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Measuring the Horopter

• Measurement problem It is difficult to
  stimulate retinal points directly in human
  subjects. As a result there are a variety of
  techniques for indirect measurement.

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Issues in Measurement

• Corresponding points give rise to the same visual
  direction
• Corresponding points should be perceived as the
  same distance for the subject
• Corresponding points should have zero disparity.
  If they fall outside of Panum's area then you
  will see diplopia.
• Images that are displaced from the horopter will
  have crossed or uncrossed disparity.

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Issues in Measurement

• Corresponding points give rise to the same visual
  direction
• Corresponding points should be perceived as the
  same distance for the subject
• Corresponding points should have zero disparity.
  If they fall outside of Panum's area then you
  will see diplopia.
• Images that are displaced from the horopter will
  have crossed or uncrossed disparity.

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Issues in Measurement

• Corresponding points give rise to the same visual
  direction
• Corresponding points should be perceived as the
  same distance for the subject
• Corresponding points should have zero disparity.
  If they fall outside of Panum's area then you
  will see diplopia.
• Images that are displaced from the horopter will
  have crossed or uncrossed disparity.

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Issues in Measurement

• Corresponding points give rise to the same visual
  direction
• Corresponding points should be perceived as the
  same distance for the subject
• Corresponding points should have zero disparity.
  If they fall outside of Panum's area then you
  will see diplopia.
• Images that are displaced from the horopter will
  have crossed or uncrossed disparity.

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How to measure

• 5 different horopter criteria
• Identical visual direction
• Apparent Fronto-parallel plane
• Singleness
• Stereoacuity
• Zero vergence

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Identical visual direction

• When two targets (one presented to each eye) are
  perceived as lying in the same visual direction.

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Apparent fronto-parallel plane

• The locations perceived as lying the same
  distance from the subject as the fixation point.
  This is the easiest to measure.

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Singleness

• This takes advantage of Panums area. Objects
  within Panums area will be seen as single. The
  horopter points lie in the middle in the region
  of single vision.

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Stereoacuity

• The region where you have maximum stereoacuity.

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Zero vergence

• Points in space seen as equidistant will not
  stimulate motor fusion.

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Typical horopter findings

• The measured horopter does not match the Vieth
  Muller circle.

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Measured Horopter

• Perception of space
• Compensation for perception of space

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