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Module 4: Neuro > Optical System III > Flashcards

Optical System III Flashcards

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1
Q

What does the lens do to an image when it projects it on the retina?

A

The image is inverted and reversed

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2
Q

What field of vision does each side of the eye receive?

A

nasal = ipsilateral

temporal = contralateral

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3
Q

What visual field is transmitted throught he left optic tract? The right?

Where is it projected to?

A

Left = right visual field; projected to left LGB

Right = left visual field; projected to right LGB

–> the ipsilateral nasal fields decussate at the optic chiasm

LGB = lateral geniculate body

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4
Q

What are the two main pathways of the lateral geniculate body?

A

Magnocellular (layers 1 and 2)

Parvocellular (layers 3-6)

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5
Q

How doe the LBG magnocellular and parvocellular pathways differ in the following visual processing information:

Ganglion cell input

LGB relay site

Target to which it responds best

Color sensitivity

Acuity

A
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6
Q

What can cause lesions of the visual pathways?

A

Cerebral vascular accidents to the ICA, Circle of Willis and Posterior Cerebral Artery

Pituitary tumors

Intracerebral tumors (i.e. meningiomas)

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7
Q

What lesion would produce Total blindness in the right eye?

A

Severing the right optic nerve

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8
Q

What lesion would cause Bitemporal Heteronymous Hemianopsia?

A

AKA tunnel vision

A lesion to the optic chiasm (i.e. pituitary tumor)

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9
Q

What lesion would cause Left homonymous hemianopsia?

A

severing the right optic tract (or complete severing of right optic radiations)

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10
Q

What would cause left superior quadrantanopsia?

A

A lesion in the more posterior arc of the optic radiations (leaving the anterior intact)

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11
Q

What is the dorsal pathway in visual processing?

A

“Where” or “M-pathway”
- M-ganglion cells of retina –> M layers (1-2) of LGB –> layer IV of V1
Continues as dorsal pathway to the visual cortex
- terminates in superior parietal cortex

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12
Q

What is the ventral pathway in visual processing?

A

“What” or “P-pathway”
- P-type ganglion cells of retina –> P-layers (2-6) of LGB –> layer IV of V1
Continues as ventral pathway and terminates in Inferior Temporal Cortex (ITC)

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13
Q

What are the functional characteristics of the Dorsal pathway of visual processing?

A

Characteristics:

  • Large receptive fields
  • high temporal resolution
  • responds to moving or changing stimuli
  • Low spatial resolution

Functions:

  • Motion detection
  • Depth Perception/spatial analysis
  • Visual Attention
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14
Q

What are the functional characteristics of the ventral pathway of visual processing?

A

Characteristics:

  • Small receptive fields
  • low temporal (frequency) resolution
  • high spatial resolution

Function:

  • Object recognition
  • Visual perception and memory
  • Color processing
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15
Q

What is visual agnosia?

A

inability to recognize and identify objects or persons without a loss of visual acuity

  • lack of concious perception of object
  • inability to link visual perception with meaningful experience
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16
Q

What can cause visual agnosias?

A

Infacts of PCA or MCA

tumors

CO poisoning

(often bilateral lesions)

17
Q

What is Simultanagnosia?

A

inability to perceive more than one object at the same time

(lesion in the dorsal pathway)

18
Q

What is akineptopsia?

A

loss of motor perception (“motion blindness”) or inability to recognize movement

  • lesion in dorsal pathway
19
Q

What is prosopagnosia?

A

inability to identify faces
(“face blindness”)

  • lesion in the ventral pathway
20
Q

What is Cortical Color Blindness (Achroatopsia)?

A

loss of color vision despite the presence of normal functioning cones

  • lesion in the ventral pathway
21
Q

What are saccade movements?

A
  • Rapid movements
  • Move eyes to a new visual target
  • Direction and distance pre-calculated
  • No feedback used during movement
22
Q

What are characteristics of smooth eye movements?

A
  • slow (“continuous”) conjugate movements
  • Keep images stabilized on retina
  • Require sensory information
23
Q

How will a patient present with a right abducens nerve lesion when the patient attempts to gaze:

Forward

Right

Left

Converge

A

Forward:
Right eye is adducted
(strabismus and horizontal diplopia)

Right:
Left eye adducts
Right eye only to mid-point
(strabismus and horizontal diplopia are max)

Left:
Left eye abducts
Right eye adducts
(NO strabismus, NO diplopia)
NOT impaired

Convergence:
NOT impaired

24
Q

How will a patient present with a right abducens nucleus lesion when the patient attempts to gaze:

Forward

Right

Left

Converge

A

Forward:
Both eyes deviate to left
(NO strabismus)

Right:
Both eyes only go to midpoint
(paralysis of lateral gaze to side of lesion)
(NO strabismus)

Left:
Left eye abducts
Right eye adducts
(NOT impaired)

Convergence:
Not impaired

25
Q

How will a patient present with a Left MLF lesion when the patient attempts to gaze:

Forward

Right

Left

Converge

A

Forward:
Left eye is turned outward
(strabismus and horiz. diplopia)

Right:
Right eye abducts
Left eye only to midpoint
(strabismus and horiz. diplopia max)
Monocular nystagmus in right eye

Left:
Right eye adducts
Left eye abducts
(NOT impaired)

Convergence:
NOT impaired

26
Q

Where do most lesions of the trochlear pathway occur?

A

After deccussation on the nerve

The trochlear nucleus innervates the contralateral superior oblique muscle and tracts cross almost immediately after leaving the brainstem

27
Q

How will a patient present with a right trochlear nerve lesion when the patient attempts to gaze:

Forward

Left

Left and Down

A

Forward:
Right eye is elevated adducted and extorted
(oblique diplopia)

Left:
Right eye is elevated
(vertical diplopia)

Left and Down:
Right eye unable to depress
(max vetical diplopia)

compensatory head tilt to opposite side of the lesion

28
Q

How will a patient present with a right oculomotor nerve lesion looking forward?

A

Right eye is shut
(complete ptosis)

Left eye normal

Open eyelid:
Right eye is down and out
right eye pupil is fully dilated
Left eye normal

29
Q

What does the oculomotor nuclear complex innervate?

A

LMNs:
Superior Rectus
Medial Rectus
Inferior Rectus
Inferior Oblique
Levator Palpebrea Superioris

Parasympathetics:
(Edinger-Westphal Nucleus)
Ciliary Body
Sphincter pupillae

30
Q

How will a patient present with a right CN III lesion?

A

Right Eye:
Closed
Pupil dilated
Eye “down and out”
(only lateral rectus and superior oblique are working)

Left Eye:
Normal

(Patient facing forward)

31
Q

What is the pathway of the pupillary light reflex and what does it test?

A

Tests: CN II (sensory) and CN III (motor)

The light is shown into eye and CN II relays info back to the Rostral Midbrain –> Excitation of the Edinger-Westphal nucleus results in synapses sent to the ciliary ganglion –> leading to pupillary constriction

32
Q

How will a patient present with a Right CN III lesion react to the pupillary light reflex?

A

Shine light in Right eye:
- No direct response in R eye
- Consensual response in L eye
(CN II is working, but CN III isn’t)

  • *Shine light in Left eye:**
  • Direct response in L eye
  • No consensual response in R eye
33
Q

What are the Cortical Eye Movement Areas and what do they do?

A

Frontal Eye Field:
Voluntary Saccades
(vertical and contralateral)

Posterior Parietal Area:
Visually guided saccades

–> Both connect directly to the contralateral gaze centers (via superior colliculus)

Module 4: Neuro (17 decks)

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