53 Eye Movements

Question 1

describe optokinetic reflex

Answer 1

• optokinetic reflex movements occur when you are sitting in a train and watch the landscape outside
• this reflex keeps an object in the center of your visual field as long as possibly by keeping your eyes pointed toward this object

Question 2

describe saccadic eye movements

Answer 2

• shifts the direction of gaze from one visual target to another visual target; forms the initial step in (lateral) gaze

Question 3

Answer 3

Question 4

describe the frontal eye field in the cortex

Answer 4

• the frontal eye field is located in area 8 of the frontal lobe
• its lcoation alone suggests its role in the planning and initiation of eye movements
• it plays a central role in the control of voluntary eye movements, in particular, saccadic eye movements

Question 5

describe the parieto-occipital eye field

Answer 5

• the parieto-occipital eye field is located in the area of the junction of the parietal lobe and the occipital lobe
• from the primary visual cortex onwards the dorsal (parietal) pathway for motion (and depth) led up exactly into this area
  
  • the output from this area is involved in eye movements related to motion of the whole visual surround (optokinetic movements) or movements following a moving target (smooth pursuit)

Question 6

Answer 6

Question 7

describe the neural pathway of saccadic eye movements

Answer 7

• the frontal eye field is the planning region and the trigger for saccadic eye movements
• descending fibers originating in the frontal eye field cross the body’s midline in the pons and synapse on neurons in the pontine paramedian reticular formation (PPRF) on the contralateral side
• cells in the PPRF activate the adjacent abducens nucleus
• the output from the abducens nucleus is twofold:
  
  1. some fibers ofrm the abducens nerve and innervate the lateral rectus inducing abduction
  2. other fibers cross the body’s midline immediately after exiting the abducens nucleus and ascend in the contralateral medial longitudinal fasciculus (MLF) until they reach the oculomotor nucleus which then innervate the medial rectus muscle inducing adduction

Question 8

describe what is seen

Answer 8

fibers from CN IV cross the body’s midline and ascend in the contralateral medial longitudinal fasciculus (MLF) until they reach the oculomotor nucleus (CN III)

Question 9

describe internuclear ophthalmoplegia

Answer 9

• internuclear ophthalmoplegia is based on a lesion of the medial longitudinal fasciculus (MLF) which prevents adduction of the eye on the side of the lesion during attempted lateral gaze

Question 10

describe what is seen

Answer 10

patient with a lesion of the left MLF (adduction of the left eye is impaired)

convergence does not involve the MFL and is not affected by the lesion

Question 11

describe a PPRF lesion

Answer 11

• lesions of the PPRF result in a paralysis of ipsilateral horizontal eye movements
• conjugate horizontal gaze towards the side of the lesion is interrupted
• when the left PPRF is damaged, horizontal eye movements of both eyes towards the left are impaired (left gaze palsy)
• vertical gaze can still be intact

Question 12

describe one and a half syndrome

Answer 12

• a combination of gaze paralysis in one direction (counts for the “one”) and internuclear ophthalmoplegia in the other direction (counts for the “half”, since one eye is still able to move but not the other)
• abduction is intact only in one eye
• it is caused by an extensive PPRF lesion and MLF on one side of the brainstem

Question 13

describe what would be seen during the red glass test

Answer 13

Question 14

Answer 14

Question 15

Answer 15

Question 16

Answer 16