Binocular Vision: Lecture 9: Horopter 1

Question 1

1. What is it: A Volume centered on the fixation point that has all points in space that YIELD SINGLE VISION?
   a. Each different fixation distance has its own what?

Answer 1

1. the HOROPTER

a. Own Vieth-Muller Circle

Question 2

Horizon of Vision

1. What is it: Locus of ALL Points in visual space that are imaged on Corresponding points in EACH eye when the eyes are CONVERGED to aim at a specific Fixation point is CALLED…?
2. What is it: Set of all points in Visual Space that are imaged onto corresponding points in each retina also appear to be at the SAME DISTANCE from the observer as the Fixation point, having ZERO DISPARITY is called what?

Answer 2

1. Theoretical Point Horopter

2. EQUIDISTANT HOROPTER

Question 3

Horopter

1. The Horopter is a way to represent how we PERCEIVE what?
2. The Theoretical Point Horopter EXTENDS how from the FIXATION POINT?
3. What do the 2 foveas represent?

Answer 3

1. 3-D Visual Space
2. Horizontally AND Vertically
3. Each represents the Oculocentric Primary Visual Direction. They are CORRESPONDING POINTS

Question 4

1. What is it: Set of ALL POSSIBLE Pairs of Corresponding points that would be stimulated by Objects lying ANYWHERE on a Circle that Intersects the Fixation Point and the Nodal Points of the Two Eyes?

a. What does this predict?
b. How?

Answer 4

1. VIETH MULLER CIRCLE
   a. the Shape of the Horopter
   b. just by GEOMETRY, or ANGULAR ARRANGEMENT of corresponding points in each eye.

Question 5

1. What is it: Binocular viewing conditions: A Vergence response occurs that moves the horopter near to the fixation target, to prevent Dipolopia and Ensures Sensory Fusion?
2. What is it: Fixation target moves off the Horopter, now being imaged on Non-Corresponding points. This Non-Zero Horizontal Disparity will initiate a reflexive vergense response to REDUCE or ELIMINATE Horizontal Disparity. This is called…?

Answer 5

1. The FUSION REFLEX

2. Disparity Vergence (AKA the FUSION REFLEX)

Question 6

How to Measure the Horopter

1. When we have Convergence Symmetrically fixed on a Given Fixation Target (target is on midline b/w the 2 eyes), what can we map out?
2. Corresponding Points
   a. Do they have Binocular Disparity? Why or why not?

b. They are perceived as having IDENTICAL or Non-Identical Visual Directions in the 2 eyes?
c. So, ALL Points ON the Horopter will have what kind of DISPARITY? They are seen how?
3. What does the Horopter represent in Visual space as we fixate a specific point?

Answer 6

1. Horizontal Location of ALL Points in physical space whose images stimulate CORRESPONDING RETINAL POINTS
2. a. NO. Because points are perceived as being at the SAME DISTANCE from the eye as the FIXATION POINT!
   b. Identical visual directions in the 2 eyes.
   c. ZERO DISPARITY: seen in a FLAT PLANE equidistant to the Fixation point, so NO FUSIONAL Eye Movements are needed
3. the locations in Visual space of the BOUNDARIES B/W CROSSED and UNCROSSED DISPARITIES!

Question 7

Horopter (2)

1. When will the horopter become the place in space where we are MOST SENSITIVE to changes in DEPTH?
   a. What will Objects appear to do?
2. We usually measure the Horopter with the eyes fixating a Target at the Same what as the eyes?
   a. With a Fixation rod at what spot?
   b. We do this to ENSURE what?

Answer 7

1. as DISPARITY changes SIgn from Crossed to Uncrossed.
   a. They will appear to change from BEING CLOSER than the fixation point to FARTHER AWAY than the FIXATION POINT
2. at the same VERTICAL HEIGHT
   a. and a fixation rod at a specific distance from the observer along the Vertical Midline of the Head.
   b. ENSURE SYMMETRIC CONVERGENCE (same angle of vergence in EACH EYE!)

Question 8

Horopter Criteria (5 Criteria)

1. When 2 Targets, Each presented to one eye, are perceived as Lying in a SINGLE Visual Direction, the IMAGES of those targets have to be Formed on CORRESPONDING RETINAL POINT?
2. Locations perceived as lying at the same distance from the Observer as the Fixation point
   a. Every point on this Horopter is perceived as lying in a PLANE PARALLEL to the Subject’s Head and EQUIDISTANT from it at the Same Distance as the Fixation Point
3. Objects on or near the Horopter that are SEEN SINGLY;
   a. Those far removed form the horopter in either direction will be what?
4. The Finer the Stereoscopic Threshold, the Closer a Point is in space to the Horopter
5. Points in space seen as Equidistant will not stimulate a Motor Fusional Response
6. Of these Criteria, which 2 are MOST COMMONLY USED?

Answer 8

1. IDENTICAL VISUAL DIRECTIONS
2. EQUIDISTANCE (or STEREOSCOPIC DEPTH MATCHING)
   a. APPARENT FRONTOPARALLEL PLANE (AFPP)
3. SINGLENESS (HAPLOPIA)
   a. Diplopic
4. MINIMUM STEREOACUITY THRESHOLD
5. ZERO VERGENCE
6. IDENTICAL VISUAL DIRECTION and STEREOSCOPIC MATCHING (AFPP)

Question 9

Experimental Methods for Determining the Empirical Longitudinal Horopter

1. Nonius Method: What do you do? (2 lines are seen)
   a. If lines are on the horopter?
   b. In front?
   c. Behind? (what will pt see)’
2. So when the 2 half-views of the test rod are perceived as ALIGNED, they’re seen how?
   a. What is difficult to measure, but is considered to be the ONLY truly Correct Horopter Criterion?

Answer 9

1. Find a Point in SPACE where Monocular Visual Directions are the SAME!
   a. The two lines will line up
   b. The Top Line is to the LEFT
   c. Top line is to the RIGHT
2. Identical Visual directions and thus stimulate corresponding Points in the 2 eyes
   a. Identical Visual Direction Horopter (only one that directly measures identical visual direction…the true definition of corresponding points)

Question 10

Nonius (IVD) Horopter (2)

1. Each eye views the test rod thru what?
   a. What does this allow each eye to see?
   b. This technique is known as what?
2. What is marked then?
3. If this procedure is REPEATED for SEVERAL LATERAL Positions or Eccentricities of the measuring rod from the fixation point in a horopter apparatus, what is PRODUCED?

Answer 10

1. thru a GRID
   a. 1 eye, then the other eye, sees alternate parts of the Rod
   b. GRID NONIUS METHOD
2. the Point in space where the 2 half-images are seen in an IDENTICAL VISUAL DIRECTION
3. a plot of the set of Corresponding points (ie. the Horopter) is Produced

Question 11

Nonius (HVD) Horopter (3)

1. What is difficult to measure?
   a. But it is the only criterion that directly measures what?

b. When will the HOROPTER INTERSECT the FIXATION ROD?

Answer 11

1. The Identical Visual Direction Horopter
   a. the Identical Visual Direction (the true definition of Corresponding points)

b. ONLY when NO FIXATION DISPARITY EXISTS!

Question 12

Apparent Frontoparallel Plane Method

1. What is it?
   a. It’s a More/Less Precise procedure for measuring the horopter?
2. When test rods physically lie in the Objective Frontoparallel Plane,
   a. They may be perceived as curving away from the Observer. What will the subject do they are perceived as BEING IN the FRONTOPARALLEL PLANE?
   b. What does this cause the rod settings to do?
   c. So the Rod positions follow the shape of what?

Answer 12

1. The Equal-Distance or Stereoscopic Depth-Matching horopter.
   a. More Precise
2. a. They will move the RODS INWARD
   b. Cause the rod settings to CURVE INWARD
   c. they follow the Shape of the HOROPTER!

Question 13

Apparent Frontoparallel Plane Method (2)

1. In the AFPP Horopter, the subject views a number of rods while fixating the middle rod. The subject then adjusts the distances of ALL of the rods, until they appear to be what?
2. The Horopter itself will be what?
   a. What will the patient perceive though?
3. When subjects move a ROD CLOSER THAN FIXATION, they do this because the HOROPTER is located where?
4. The AFPP Method Reflects the Effects of what?

Answer 13

1. to be at the Same Distance away as the middle rod in a Plane PARALLEL to the Subject’s Face
2. curved.
   a. a FLAT PLANE of rods
3. It’s FARTHER AWAY from Fixation, and they’re trying to compensate for this by moving the rods inward to make their positions appear in alignment to them.
4. of FIXATION DISPARITY!

Question 14

Singleness Horopter

1. The arrangement of the rods is similar to that for measuring the what?
   a. One rod is always what?
   b. Then a second test rod is moved how? Until what happens?
   c. This process is repeated for what?
2. The width of the ZONE of SINGLENESS reflects what AREA?
   a. What is this?

Answer 14

1. of the AFPP Horopter
   a. FIXATED
   b. CLOSER to the Subject, until Diplopia is reached (rod first appears double)
   c. rods that are further away.
2. Panum’s AREA
   a. represents the zone of singleness surrounding corresponding points in which NONCORRESPONDING POINTS are still seen as SINGLE!

Question 15

The Maximum Stereoacuity Horopter

1. What is it?
2. How do we measure it?
   a. So by using this, we are DETERMINING what?
3. To measure it, Start with the TEST ROD where?
   a. Then move it in Depth until the subject perceives it as being where?
   b. Repeat this for what?
4. The location in SPACE at which the VARIANCE is SMALLEST/LARGEST corresponds to the location of that ECCENTRIC POINT on the HOROPTER.
   a. We are SENSITIVE to DISPARITY when we are CLOSE to what?
5. Problem with this test?

Answer 15

1. MINIMUM stereoacuity Threshold
2. Fixate a CENTRAL ROD while measuring Stereoscopic Threshold for a SECOND, More ECCENTRIC ROD
   a. the SMALLEST STEREOSCOPIC DISPARITY or CHANGE in DEPTH than can be DETECTED for THAT ROD!
3. At the SAME PERCEIVED DISTANCE as the FIXATION POINT
   a. At a Different Distance
   b. For different Target Distances
4. where it’s SMALLEST
   a. Close to ZERO DISPARITY
5. TIME CONSUMING and DIFFICULT!

Question 16

Zero Vergence Horopter Criterion

1. Most DIFFICULT to measure. Why?
2. When does the Test Target Elicit a Motor Fusional Response from the Subject?
3. The Vergence System Attempts to MINIMIZE what?

Answer 16

1. It needs Measurements of VERY SMALL FUSIONAL MOVEMENTS of the EYES using Sensitive Objective Eye Movement Recording Equipment
2. When the Test Target Falls on NONCORRESPONDING POINTS in the 2 Eyes.
3. The Amt of DISPARITY in the Test Target