Ocular Reflex Testing

Question 1

describe the afferent limb of the optokinetic reflex

Answer 1

• the optokinetic reflex is based on visual input, following the visual pathway up to the primary visual cortex (V1)
  
  • the magnocellular pathway carries info. of movement
• from V1, the dorsal stream carries visual info. of motion to the parieto-occipital eye field
• objects moving to the right activate the right parieto-occipital eye field

Question 2

describe the efferent limb of the optokinetic reflex

Answer 2

• fibers originating in the right parieto-occipital eye field activate right pontine nuclei
• fibers originating in these nuclei activate the left vestibulo-cerebellum (flocculo-nodular lobe)
• the left vestibulo-cerebellum in turn activates the left vestibular nuclei
• from the left vestibular nuclei onwards, the pathway is identical to the vestibulo-ocular reflex
  
  • activates the right abducens nucleus and nerve, when then activates the left MLF and the left oculomotor nucleus and nerve, inducing conjugate horizontal eye movement to the right

Question 3

draw the efferent limb of the optokinetic reflex

Answer 3

Question 4

slow movements are triggered by the _____ reflex

fast movements are triggered by _____

Answer 4

slow movements are triggered by the optokinetic reflex

fast movements are triggered by saccadic reset

Question 5

describe the relfex and the direction of nystagmus during the start of rotation to the right

Answer 5

• VO nystagmus is to the right
  
  • slow nystagmus is to the left

Question 6

describe the reflex and direction of nystagmus during continued rotation to the right

Answer 6

• OK nystagmus is to the right
  
  • slow nystagmus is to the left

Question 7

describe the reflex and direction of the nystagmus when rotation is stopped (originally to the right)

Answer 7

• VO nystagmus to the left
  
  • slow nystagmus to the right

Question 8

describe the pupillary light reflex circuitry

Answer 8

• shining light into the right eye activates retinal ganglion cells
• the axons of retinal gang. cells form the afferent limb of the reflex arc
• about 50% of the fibers forming the optic nerve stay ipsilateral and continue in the optic tract of the same side, while the other 50% gang. cell axons cross at the optic chiasm and then run along the contralateral optic tract
• not all fibers carrying visual info. synpase in the LGN; some fibers synapse in the pretectal nucleus of the midbrain
• collaterals of axons originating in the pretectal nucleus bilaterally innervate the EW nuclei, which are the accessory nuclei of CN III

Question 9

Answer 9

Question 10

describe the pathway for pupillary light reflex

Answer 10

Question 11

describe the corneal reflex circuitry

Answer 11

• when sensory endings of nociceptors located in the cornea are activated, their sensory signal enters the pons via the ophthalmic division of the trigeminal nerve (V-1)
• the fibers descend within the pons and medulla to synapse in the spinal nucleus of CN V
• fibers originating from there activate (directly and indirectly) both facial nuclei located in the lower pons

Question 12

Answer 12

• when sensory endings of nociceptors located in the cornea are activated, their sensory signal enters the pons via the opthalmic division of the trigmeninal nerve (V-1)
• the fibers descend within the pons and medulla (similar to pain traveling via trigeminal) to synapse in the spinal nucleus of CN V
• fibers originating from spinal nucleus of CN V activate directly and indirectly both facial nuclei located in the lower pons