Name _________________________

1. At the abathic distance, the AFPP horopter is (1)
A. inside the Vieth-Müller circle and concave toward the observer.
B. on the Vieth-Müller circle.
C. concave toward the observer, but beyond the Vieth-Müller circle.
D. coincident with the objective fronto-parallel plane.
E. convex away from the observer.

 2. The circle which contains the two nodal points and the fixation point is known as the (1)
A. empirical horopter.
B. Shipley-Rawlings plot.
C. the circle of least confusion.
D. the Hering-Hillebrand deviation
E. the Vieth-Müller circle.

 3. Which of the following is NOT an advantage of binocular vision? (1)
A. superior depth perception in all viewing conditions.
B. larger field of view.
C. greater sensitivity resulting from summation from two detectors.
D. an extra eye in the event that one eye is damaged.
E. better space perception, especially within arm's length.

 4. Briefly describe any disadvantages to having a binocular versus a monocular visual system. (2)

• It requires more complex neurological support, coordination and analysis.
• With a more complex system, there's more that can go wrong.
• Certain eye problems come from anomalies which can only exist in a binocular system; examples include diplopia, aniseikonia, binocular imbalance, convergence insufficiency, etc.

5. For which of the following occupations or activities would stereopsis be MOST beneficial? (1)
A. Military fighter pilot.
B. UPS truck driver
C. tailor
D. deer hunter
E. professional boxer

 6. In the study of binocular vision, what is meant by the term egocentric localization? (2)

• Perceptual localization of objects relative to a point in the head (the egocenter)
• Based on directional input from two eyes
• Egocenter located (in theory) midway between the two nodal points

7. What is meant by oculocentric localization and local sign? (2)

• Sense of direction relative to the fovea of one eye
• Based on retinal location of the image
• Local sign is the retinal direction associated with a object

8. In normal binocular vision, our ultimate, or final sense of visual direction is (1)
A. egocentric.
B. oculocentric.
C. the same as the local sign.
D. non-cyclopean.
E. based on the non-dominant eye.

 9. Based on the integration of local sign and eye position information, why does a person with esophoria perceive against motion with the alternate cover test? Draw diagrams to help explain your logic. (5)

• The visual system receives local sign direction information from both eyes.
• It also receives information on the eye's orientation in computing egocentric visual directions.
• When the cover is over OS, OD is foveally fixating, while OS is turned to the right.
• The object appears to be located on the cyclopean eye visual axis, but the cyclopean eye axis is tilted slightly to the right.
• The object therefore appears to be located slightly to the right.
• When the cover is moved to cover OD, OS will foveally fixate, while OD will turn to the left.
• The object appears to fall on the cyclopean axis, but the cyclopean is turned slightly to the left.
• The object therefore appears to be located slightly to the left now.
• So, in moving the cover paddle from left to right, the object's apparent location shifts from right to left (against motion).

10. Which kind of binocular eye movement is primarily involved when a hunter follows a flock of ducks flying from left to right at 100 meters? (1)
A. Vergence
B. Version
C. Major contribution from both vergence and version
D. Accommodation
E. Cyclophoria
 

11. Which kind of binocular eye movement is primarily involved when a baseball shortstop sees a line-drive fly from the batter directly toward his face? (1)
A. Vergence
B. Version
C. Major contribution from both vergence and version
D. Accommodation
E. Cyclophoria

 12. On the following diagram, illustrate how vergence and version subsystems work to change fixation from point a to point b, when both the distance and direction change. Do this by drawing the trajectory of the intersection point for the visual axes. (3)

• Show that the eyes initiate a vergence movement,
• followed by a rapid version and
• a final vergence onto the new fixation point.

13. List and define each of the six types of vergence movements which we studied in class. (12)

• Disparity vergence - reflexive vergence stimulated by retinal disparity
• Accommodative vergence - vergence which accompanies accommodation
• Tonic vergence - resting vergence posture of the eyes when they are NOT fixating.
• Vergence adaptation - vergence which builds up over time and substitutes for disparity vergence
• Proximal vergence - vergence stimulated by the perceived proximity of an object
• Voluntary vergence - deliberate, conscious vergence

14. A medical laboratory technician who uses a binocular microscope several hours each day complains of eye strain and occasional double vision during work. Assuming that he/she is emmetropic, this may be due to (1)
A. Meridional ambyopia
B. Aniseikonia
C. Keratoconus
D. Instrument vergence / myopia
E. Poor stereo acuity

 15. Which of the following is associated with the idea of utrocular discrimination? (1)
A. Fixation disparity
B. Bias
C. Eye signature
D. Disparity vergence innervation
E. Corresponding points

 16. If Mr. Elway throws you a football from a distance of 50 meters, at what distance (from you) will you first be able to perceive the ball's relative distance, using stereopsis? Assume that your stereoacuity threshold is 20 arc seconds and your PD is 64 mm. Give your answer to the nearest 0.1 meters. (1)

Approximately 46.5 meters away.
 

 17. What is the horopter? (2)

Any of the following:

• Locus of points in space which stimulate corresponding retinal points.
• Also, the location of objects in space which give rise to zero retinal disparity.
• Points in space which have identical oculocentric visual directions in each eye.

18. Which of the following consists of an arc in the horizontal plane and a vertical line, both of which intersect the fixation point? (1)
A. Vieth-Müller circle
B. Longitudinal horopter
C. Point horopter with a peripheral fixation point
D. Point horopter with a central fixation point
E. Nonius horopter

 19. What does the Hering-Hillebrand deviation suggests about the possible distribution of corresponding points on the two retinas? (1)

• We cannot assume nasal-temporal symmetry

20. In theory, why is the Nonius technique a more direct way to measure the true horopter than the AFPP method? (2)

• The Nonius technique finds the points in space which have identical visual directions in the two eyes. This is one definition of the horopter.
• The AFPP method assumes that points on the horopter will appear to lie in a plane parallel to the observer's face. This may or may not be true.

21. If a patient received new spectacles, which cause relative minification of the left eye's image (i.e., OD -3.00 D, OS -6.00 D), how should their space perception be distorted, based on what we learned about the horopter? (1)
A. A wall parallel to their frontal plane would appear tilted away from their right side.
B. A wall parallel to their frontal plane would appear tilted toward their right side.
C. A wall parallel to their frontal plane would appear tilted away from their left side.
D. A wall parallel to their frontal plane would appear be symmetrically curved toward them.
E. A wall parallel to their frontal plane would appear in the objective fronto-parallel plane.

 22. Assuming optimal test conditions, what is the angular width of Panum's space on either side (distal and proximal) of fixation? (1)
A. 2-5 arc seconds
B. 6-10 arc seconds
C. 2-5 arc minutes
D. 6-10 arc minutes
E. Approximately 1 degree
 

23. Under ideal test conditions, what is the stereoscopic threshold on either side (distal and proximal) of fixation? (1)
A. 2-10 arc seconds
B. 20-40 arc seconds
C. 2-10 arc minutes
D. 20-40 arc minutes
E. Approximately 1 degree

 24. What is a fixation disparity? (2)

• Very small misalignment of the eyes, with respect to fixation (usually < 5-6 arc minutes).
• It occurs during bifoveal fixation and binocular fusion.

25. Name three important features which must be included in any test that will diagnose the direction and magnitude of a fixation disparity. (3)

• Central fixation lock, preferably 1.5 degrees wide
• Lines straddling the center, which are seen simultaneously, though monocularly, by each eye.
• A systems to measure the angle of deviation; perhaps calibrated lines.

26. Assuming that you use a Wesson card to test a patient with a right hyper fixation disparity. If you rotate the card so that the left line is seen by OS, what should the patient see? Draw a simple picture. (1)

27. Using a Sheedy Disparometer, how would you have to adjust the test lines in order to make them appear aligned for the patient in Question 26? Draw a simple picture. (1)

28. Draw a standard forced vergence-fixation disparity graph showing the response of a patient with a (4)

• Type III response
• 3 arc minute exo fixation disparity
• 5 &#144; BI associated phoria
• Very little vergence adaptation in play

29. What is the normal range of values expected for a fixation disparity? (1)
A. 2 exo to 2 eso
B. 5 exo to 5 eso
C. 6 exo to 4 eso
D. 4 exo to 6 eso
E. 10 exo to 10 eso

 30. In theory, how does a small amount of fixation disparity help the visual system maintain stable fixation? (3)

• Fine disparity vergence requires some retinal disparity to be stimulated.
• If the fixation disparity went to zero, the stimulus for disparity vergence would be lost.
• The eyes would then drift toward their position of rest, until enough retinal disparity was again detected.
• Only then would disparity vergence resume.
• This would lead to an unstable fixation with micro-oscillations.
• A constant amount of residual fixation disparity ensures the disparity vergence system remains active.
   

   

BONUS POINTS

What are some possible optical complications of refractive surgery? (2)

• Significant increase in higher order optical aberrations.
• This can cause a reduction in vision for low contrast objects.
• Also, it may reduce vision in low illumination.
• Many refractive surgery patients have impaired night vision. Many can no longer drive at night.

Describe the principle of the Shack-Hartmann wavefront sensor. (5)

• A point source of light is placed on the retina.
• Light reflected out of the eye is sub-divided by tiny micro-lenslets.
• Each lenslet forms a dot image of the retinal point source.
• The shift of the dot images is used to compute the wavefront aberration function of the eye.

How are Zernike polynomials used in visual optics? (3)

• This is a systematic way to describe the wavefront aberration function.
• It is based on a mathematical decomposed of the wavefront data into basic components