Ocular Motility: Lecture 11: OKN

Question 1

Overview of VOR

1. OKN is induced REFLEXIVELY by what?
   a. This causes what?
2. Function of OKN is to SUPPLEMENT what?
   a. OKN Maintains Retinal Image Stability during what?

Answer 1

1. Motion of a Large Visual Scene
   a. an Illusionary Sensation of Self-rotation (Circularvection) in the OPPOSITE DIRECTION
2. the Angular VOR
   a. during Sustained, Low-Frequency Rotation

Question 2

Overview of VOR (2)

1. When a Normal Subject sits w/Head still inside a Large, Patterned, Revolving Drum, what develops?
2. If lights are suddenly turned off, does the Nystagmus stop?
3. OKAN time constant is how long?

Answer 2

1. Optokinetic Nystagmus Develops
2. Not immediately. Gradually Fades away as Optokinetic After-Nystagmus (OKAN)
3. -5 to -50 seconds

Question 3

Overview of VOR (3)

1. During Sustained Head Rotation in the Dark, Vestibular Nystagmus Subsides Over what?
   a. If the rotation is suddenly stopped, what happens?

Answer 3

1. over 60 seconds as Cupula returns to its original position
   a. PVN begins w/slow phases in the Opposite Direction

Question 4

Overview of VOR (4)

1. To Develop OKN Stimulation Optimally, one should have what?
2. The Initial 1 or 2 seconds of response, which already attain MAXIMAL VELOCITY (G = 0.8), is probably due to what?
   a. What dominates?
3. What part of the Retina dominates the response?
   a. What Primarily Drives the Response?

b. Is OKN response affected by blur?

Answer 4

1. a LARGE FIELD OF MOTION (like an encircling striped drum), a Relatively PASSIVE SUBJECT w/no desire to pursue any particular element of the Display and Velocity, as the relevant stimulus dimension
2. to Pursuit System Activation
   a. OKN system dominating
3. Peripheral Retina
   a. Low Spatial-Frequency Content of the Stimulus
   b. NO

Question 5

OKN Gain (1)

1. Latency time?
2. the OKN Response Starts TOO LATE to prevent what?
3. The Gain Progressively Declines from 100 for a target velocity of what?

Answer 5

1. 140 ms
2. degradation of the Retinal Image Concurrent w/the Initial Head Movement
3. of <0.01 deg/sec to 1 at 10 deg/sec to 0.2 at 70

Question 6

OKN Gain (2)

1. Gain for Horizontal and Vertical OKN is what?
   a. Although Vertical Gain does what?
2. As a function of age, OKN Max Velocity does what?

Answer 6

1. SIMILAR
   a. it Falls off slightly faster as target velocity is Increased
2. Decreases Progressively (1 deg/sec per year)

Question 7

OKN Gain (3)

1. Torsional OKN is what?
   a. Gain is what?
2. Nasalward OKN gain is what?
3. Scotopic OKN Gain is only what?

Answer 7

1. Slow and Irregular
   a. is LOW (0.03)
2. is Slightly greater (by 0.05) than Templeward OKN gain
3. only Slightly Lower (by 0.1) than Photopic OKN Gain

Question 8

Abnormal OKN System

1. In 50 Patients with Strabismic Amblyopia and Eccentric Fixation, Asymmetric OKN was found in what?

Answer 8

1. in 39 of the Amblyopic Eyes and in 25 of the fellow Dominant Eyes

Question 9

Abnormal OKN System (2)

1. Asymmetric or Reduced Gain OKN or Both in what?
2. Schor and Levi speculated that the Asymmetric OKN Nystagmus was due to Incomplete Development of what?

Answer 9

1. in Congenital Nystagmus
2. of Binocular Vision, specifically, to cortical mechanisms mediating temporally driven Optokinetic Responses, before the age of 4 years

Question 10

Testing OKN System

1. To test for static Imbalance, first inspect the eyes for what?
2. In Patients w/Peripheral Vestibular Disorders, the Nystagmus usually has a what?
   a. Because peripheral vestibular nystagmus is often suppressed by visual fixation, the nystagmus may only be seen after what?

Answer 10

1. for Primary Position Nystagmus while the patient fixes a distant target with the head stationary
2. has a Mixed Horizontal-Torsional Waveform
   a. after Fixation has been removed