Neuro-opthalmology

Question 1

Aniscoria definition

Answer 1

• difference in size (diamter) between a person’s pupils
• physiologic < 1 mm
• pathologic = efferent nervous system disturbance to innervation of muscles of the iris
• not a manifestation of vision loss

Question 2

Nervous system control of pupil size

Answer 2

• parasympathetic ==> sphincter muscle ==> pupil contraction
  
  • parasymp dysfxn ==> mydriatic pupil poorly responsive to light
• sympathetic ==> radial muscle ==> pupil dilation
  
  • sympathetic dysfxn ==> miotic pupil poorly responsive to dark

Question 3

Clinical evaluation of anisocoria

Answer 3

• goal: try to determine which pupil is abnormal

1. observe pupil sizes in light and dark
2. observe pupillary response to light

Question 4

Determining source of abnormal pupil constriction

Answer 4

• greater anisocoria in dark + normal light response = smaller pupil is abnormal (due to symp dysfxn)
• greater anisocoria in light + abnormal light response ==>
  
  • Tonic pupil due to parasymp dysfxn (if meet 3 criteria)
  • damage to iris (if 3 criteria not met + structural abnormality)
  • No tonic pupil or structural damage ==> ptosis and extraocular paresis = 3rd nerve palsy

Question 5

Criteria for Tonic Pupil

Answer 5

• greater anisocoria in light + larger pupil has poor response to light +
  1. pupil response to near target > ligth
  2. tonic dilation to distant target
  3. segmental palsy = partial iris sphincter constriction
• common cause = diabetes

Question 6

Characteristics of Horner Syndrome

Answer 6

• disruption in sympathetic fibers ==> ptosis, miosis, anhidrosis
• aniscoria = dark > light
  
  • normally pupillary response to light
  • dilation lag of miotic pupil
• 1st order = brain stem (neuron from hypothalamus to cervical spinal cord)
• 2nd order = spinal cord (cervical spinal cord to superior cervical ganglion)
• 3rd order = carotid/cavernous sinus (neuron from superior cervical ganglion to iris sphincter)

Question 7

Visual pathway

Answer 7

• optic nerve ==> optic chiasm ==> optic tract ==>
• LGN (lateral geniculate nucleus @ thalamus) ==> optic radiations ==> occipital cortex

Question 8

Hallmakrs of visual field defects from neurologic visual pathway disturbances

Answer 8

1. defect respects vertical and/or horizontal meridians (@ optic nerve or beyond)
2. defect is homonymous = involves same area of visual field in each eye (@ optic tract or beyond)
3. defect is a combo of homonymous defect + respect of vertical meridian (@ optic tract or beyond)

Question 9

Findings w/optic nerve dysfxn

Answer 9

• monocular vision loss = blurred, missing, dark
• subject color vision loss
• on exam:
  
  • vision loss of acuity, field, or both
  • unilateral defect ==> Marcus Gunn Pupil = afferent pupillary defect (AFD)
    
    • swinging flashlight test ==> less constriction/(apparent) dilation @ affected eye
  • optic nerve abnormality:
    
    • edema or pallor

Question 10

Diplopia definition

Answer 10

“double vision”

Question 11

Evaluation of diplopia

Answer 11

1. Diplopia: binocular only? (i.e. goes away when one eye is closed)
   
   1. if yes = ocular misalignment
2. Diplopia: horizontal vs. vertical
3. Diplopia: worse w/any position of gaze
4. Diplopia: worse @ near or distance viewing?

Question 12

Common cause of oscillopsia

Answer 12

• = appearance of movement of visual world due to an eye movement disturbance
• common cause = nystagmus = involuntary rhythmic oscillation of eyes
  
  • pendular: slow-slow phases
  • jerk: fast-slow phases
  • mixed: slow-slow + fast-slow
  • can be localized @ CN VIII or CNS structures (usually @ brainstem/cerebellum)