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Ophthalmology > Day 12 (2): The Afferent Visual System > Flashcards

Day 12 (2): The Afferent Visual System Flashcards

1
Q

What are the components of the bony orbit?

A

7 Bones:
1. Frontal bone
2. Maxillary bone
3. Lacrimal bone
4. Ethmoid bone
5. Sphenoid bone
6. Palatine bone
7. Zygomatic bone

ROOF: rooFS
1. Frontal bone
2. Sphenoid bone (Lesser wing)

MEDIAL WALL: SMELl
1. Sphenoid bone (Lesser wing)
2. Maxillary bone
3. Ethmoid bone
4. Lacrimal bone

LATERAL WALL: Sa Zide
1. Sphenoid bone (Greater wing)
2. Zygomatic bone

FLOOR: PaMaZa
1. Palatine bone
2. Maxillary bone
3. Zygomatic bone

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2
Q

What is the Superior Orbital Fissure?

A
  • space between the two wings of the sphenoid
  • boundary of lateral and medial wall + roof
    + Greater wing: lateral wall
    + Lesser wing: roof and medial wall

Contents: LFSTONOAS
1. Lacrimal nerve (V1)
2. Frontal nerve (V1)
3. Superior Ophthalmic Vein
4. Trochlear nerve (IV)
5. Oculomotor nerve - Superior division (III S)
6. Nasociliary nerve (V1)
7. Oculomotor nerve - Inferior division (III I)
8. Abducens nerve (VI)
9. Sympathetic nerve fibers travelling along the CN V and VI

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3
Q

What is the Inferior Orbital Fissure?

A
  • space between the maxillary bone and greater wing of sphenoid
  • separates lateral wall from floor of the orbit
    + Greater wing: lateral wall
    + Maxillary bone: floor

Contents: IGMI3ZPC
1. Inferior Ophthalmic Vein
2. Ganglionic branches: from pterygopalatine ganglion to maxillary nerve (CNV2)
3. Maxillary nerve (CNV2) –> Infraorbital nerve
4. Infraorbital artery and vein: travel along infraorbital groove –> canal –> foramen
5. Zygomatic nerve (CN V2)
6. Parasympathetic fibers: to lacrimal gland
7. Collateral Meningeal Arteries

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4
Q

What is the Optic Canal?

A
  • 8 - 10 mm long canal terminating in the orbit via the optic foramen
  • located in the LESSER WING of the sphenoid bone

Optic strut:
- part of the lesser wing of the Sphenoid bone that separates the SOF from the optic canal

Contents:
1. Optic Nerve
2. Ophthalmic Artery
3. Sympathetic nerves

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5
Q

What is the Cavernous Sinus?

A
  • one of the dural venous sinuses creating a cavity called the Lateral Sellar Compartment
  • located on both sides of the sphenoid bone and pituitary gland
  • the only anatomic location in the body where an artery completely travels through and within a venous structure
  • convergence site of the cranial nerves, ICA, pituitary gland and sphenoid sinus

Borders:
Roof: Optic nerve, chiasm and tract, ICA
Floor: Foramen lacerum, junction of sphenoid body and greater wing
Medial: Pituitary gland (in the sella turcica), Sphenoid sinus
Lateral: Temporal lobe
Anterior: Orbital apex
Posterior: Petrous temporal bone

Contents:
1. Medial wall
- Abducens nerve (CN6)
- Internal Carotid Artery
2. Lateral wall: superior –> inferior
- Oculomotor nerve (CN3)
- Trochlear nerve (CN4)
- Ophthalmic nerve (CN5A)
- Maxillary nerve (CN5B): adjacent but external

Note:
ALL nerves enter the orbital apex via the SOF except the Maxillary nerve which exits via the Foramen Rotundum

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6
Q

What is the Sella Turcica?

A
  • saddle-shaped depression in the body of the sphenoid bone
  • located postero-medial to the two orbits

Hypophyseal Fossa
- most inferior aspect
- contains the pituitary gland

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7
Q

What is the Internal Carotid Artery?

A

Internal Carotid Artery
- primary arterial supply of the intracranial contents

Segments:
1. Pars Cervicalis or Cervical portion

  1. Pars Petrosa or Petrous portion
  2. Pars Cavernosa or Cavernous portion
    - Meningohypophyseal Trunk
    + branch as ICA enters the cavernous sinus
    + supplies the dura at the back of the cavernous sinus and the cavernous portions of the CN3, CN4, CN5A, CN5B and CN6
  3. Pars Cerebralis or Supraclinoid portion
    - Ophthalmic Artery: orbit and globe
    - Anterior Choroidal Artery: optic tract, LGN
    - Middle Cerebral Artery
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8
Q

What is the Ophthalmic Artery?

A

Ophthalmic Artery
- primary arterial supply of the orbit
- arises at the supraclinoid or pars cerebralis portion of the ICA just after it becomes intradural

Branches: DR MCLESSI
Orbital group: vessels to the orbit and surrounding parts
SSLIDE
1. Lacrimal artery
2. Supraorbital artery
3. Supratrochlear artery/Frontal artery
4. Ethmoidal artery (Anterior and Posterior)
5. Internal palpebral artery (Medial and Lateral)
6. Dorsal nasal artery

Ocular group: vessels to the eye and its muscles
CAMP
1. Central retinal artery
2. Posterior ciliary arteries (Long and Short)
3. Anterior ciliary artery
4. Muscular arteries (Superior and Inferior)

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9
Q

What is the Central Retinal Artery?

A
  • first and most important branch of the ophthalmic artery
  • end artery and no collateral circulation
  • branches off before OA crosses over the ON
  • supplies the optic nerve surface and anterior 2/3 of the retina (NFL, GCL, IPL, INL)
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10
Q

What are the Posterior Ciliary Arteries?

A
  • terminal branches of ophthalmic artery + ethmoidal arteries
  1. LONG Posterior Ciliary Arteries
    - 1 nasal, 1 temporal
    - enters the eye in the nasal and temporal aspects
    - courses along the suprachoroidal and supraciliary space
    - primarily supplies the CILIARY BODY (especially Pars Plana) + anterior choroid and anterior segment
    - branches:
  2. anastomose with branches from ACA: Major Arterial Circle of Iris
  3. loops back: Recurrent Ciliary Artery to the anterior choroid
  4. SHORT Posterior Ciliary Arteries (10 - 20)
    - enters eye in the posterior aspect of globe
    - POSTERIOR CHOROID and SCLERA
    - Circle of Zinn-Haller: anastomotic ring formed by 4 SPCAs to supply the optic nerve and adjacent retina
  5. Cilioretinal Artery
    - found in only 30% of population
    - most common congenital anomaly of the retinal circulation
    - can only be differentiated from retinal arteries by FA when it fills earlier than the arterial phase
    - commonly located in the temporal edge of the optic nerve head
    - supply inner retina
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11
Q

What is the Circle of Willis?

A
  • anastomotic system of arteries that sits at the base of the brain
  • supplies the cerebrum
  • connected to the blood supply of the brainstem

Circle of Willis: CAIC PB
1. (C) Anterior Communicating Artery
2. (A) Anterior Cerebral Artery
3. (I) Internal Carotid Artery
- branches into the Middle Cerebral Artery, Ophthalmic Artery and Anterior Choroidal Artery, all of which are NOT part of the circle
4. (C) Posterior Communicating Artery
5. (P) Posterior Cerebral Artery
6. (B) Basilar Artery

Brainstem blood supply: SPA VPS
1. (S) Superior Cerebellar Artery (SCA)
2. (P) Pontine Anteries
3. (A) Anterior Inferior Cerebellar Artery (AICA)
4. (V) Vertebral Artery
5. (P) Posterior Inferior Cerebellar Artery (PICA)
6. (S) Spinal Arteries (Anterior and Posterior)

Cerebrum: Circle of Willis

Midbrain and Pons (MLF, PPRF, CN3-6 nuclei)
- Basilar Artery
- SCA
- Pontine Arteries
- AICA

Medulla:
- Vertebral Artery
- PICA
- Spinal arteries (Anterior and Posterior)

Cerebellar Peduncles:
- Superior: SCA
- Middle: AICA
- Inferior: PICA

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12
Q

What is the Optic Nerve?

A
  • bundle of 1.0 - 1.2 M axons originating from the retinal ganglion cells
  • passes the posterior scleral foramen through the pores of the Lamina Cribrosa
  • high oxygen demand thus prone to ischemia, inflammation and compression

Total Length: 50 mm or 5 cm

Segments:
A. Intraocular/Head
- shortest: 1 - 3 mm
- segment within the globe
- portion seen when doing ophthalmoscopy

Layers:
1. Nerve Fiber layer
- supply: CRA (via recurrent retinal arterioles)
2. Prelaminar layer
- supply: Circle of Zinn-Haller + SPCA
3. Laminar layer
- supply: Circle of Zinn-Haller + SPCA + Pial arteries
4. Retrolaminar layer
- supply: SPCA + Pial arteries

B. Intraorbital
- longest: 25 - 30 mm
- segment posterior to the globe upto the optic foramen
- S-shaped: longer than retro-orbital space
- supply: Pial arteries
- thicker as it becomes wrapped by:
1. Meninges: Dura, Arachnoid, Pia + subarachnoid space with CSF
+ dura fuses with the Annulus of Zinn & periosteum
+ when inflamed, causes pain on eye movement because of stretching of the meningeal attachment to the origin of EOM
2. Myelin: formed by oligodendrocytes

C. Intracanalicular
- 6 - 10 mm
- segment within the optic canal
- fixed due to fusion of dura with periosteum prior to entry into the optic canal
- NO dura; only surrounded by arachnoid & pia
- supply: Pial arteries
- most prone to bony compression due to fixed position and location within the canal

D. Intracranial
- 8 - 12 mm
- segment within the cranium
- NO dura; only surrounded by arachnoid & pia
- prone to compression by pituitary tumors and ICA aneurysms
- supply: Anterior Cerebral Artery

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13
Q

What is the Optic Chiasm?

A
  • convergence of the two optic nerves
  • L x W x H: 8 mm x 12 mm x 4 mm
  • 45-degree inclination with the anterior chiasm situated LOWER than the posterior chiasm
  • fibers from the nasal retina (~ 53%) crossover to join the temporal fibers of the contralateral retina to form the contralateral Optic Tract
    + inferior fibers: cross first and anteriorly
    + superior fibers: cross in the middle
    + macular fibers: cross last & more posteriorly
  • supply: Anterior Cerebral Artery

Adjacent structures:
- Superior: Circle of Willis and Third Ventricle
- Inferior: Pituitary Gland
- Posterior: Hypothalamus, Cerebral peduncle

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14
Q

What is the Optic Tract?

A
  • found posterior to the optic chiasm
  • formed by the contralateral nasal fibers and ipsilateral temporal fibers
  • proceed circumferentially, laterally then posteriorly around the hypothalamus and cerebral peduncles to connect with the Lateral Geniculate Nucleus
  • supply: Anterior Choroidal Artery

Pathology: Optic Tract Syndrome
1. CONTRALATERAL homonymous hemianopsia
2. CONTRALATERAL bow-tie ON pallor
3. IPSILATERAL temporal ON pallor
4. CONTRALATERAL RAPD

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15
Q

What is the Lateral Geniculate Nucleus?

A
  • FIRST termination of the retinal ganglion cells
  • location: Thalamus
  • principal thalamic visual nucleus linking the retina and cortex
  • contains 6 lamina sheets
    + layer 1, 4, 6: nasal retina of contralateral side
    + layer 2, 3, 5: temporal retina of ipsilateral side
  • terminates in V1 of striate cortex or may proceed to other areas
  • supply: Anterior Choroidal Artery and Posterior Cerebral Artery

Parts:
A. Parvocellular Pathway
- SUPERIOR/LATERAL/DORSAL 4 layers
- small soma and axons
- connects with GCs in the fovea
- SMALLER receptive field BUT sensitive to SPATIAL resolution, details and COLOR
- 90% of retinal output

B. Magnocellular Pathway
- INFERIOR/MEDIAL/VENTRAL 2 layers
- large soma and axons
- rarely connected with GCs in the fovea
- LARGER receptive field for MOTION and CONTRAST; insensitive to color
- 10% of retinal input

C. Koniocellular Pathway
- largely unknown
- sandwiched between the other layers

NOTE:
SMILe: 90-degree rotation of axons
- Superior retinal fibers –> Medial LGN
- Inferior retinal fibers –> Lateral LGN
- Macular fibers –> Supero-lateral LGN

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16
Q

What are Optic Radiations?

A

Optic Radiation/Geniculocalcarine Tract
- projection tract that connects the lateral geniculate nucleus to the primary visual cortex in the occipital lobe
- supply: Middle Cerebral Artery

3 Tracts:
1. Superior/Dorsal Radiations
- travels posteriorly
- passes through the PARIETAL lobe

  1. Inferior/Ventral Radiations
    - first travels anteriorly then laterally to loop around the temporal horn of the lateral ventricles [Meyer’s Loop] before proceeding posteriorly
    - passes through the TEMPORAL lobe
  2. Macular Fibers
    - travel on LATERAL surface of middle area
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17
Q

What is the Primary Visual Cortex?

A

Striate Cortex
- aka Visual Area 1 (V1) or Brodmann area 17
- area of the visual cortex that receives the sensory input from the lateral geniculate nucleus
- located at the MEDIAL surface of the OCCIPITAL lobe along the horizontal calcarine fissure

Orientation:
1. L side: processes R visual field
2. R side: processes L visual field
3. Macular fibers: posterior-most (tip) of cortex
4. Temporal crescent: anterior-most of cortex
- most peripheral visual field (monocular)

Supply:
1. Middle Cerebral Artery
2. Posterior Cerebral Artery –> Parieto-Occipital branch –> Calcarine artery

NOTE: Occipital Tip/Macula
- watershed area between the MCA and the Calcarine artery (PCA)

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18
Q

What are the Frontal Eye Fields?

A

Frontal Eye Fields
- aka Brodmann Area 8
- pre-motor areas of the frontal cortex
- responsible for:
+ CONTRALATERAL saccadic eye movements
+ voluntary eye movement
- communicates with EOMs via the PPRF
- supply: Anterior Cerebral Artery
- pathology:
1. gaze deviation towards IPSILATERAL side
2. poor initiation of CONTRALATERAL saccades

19
Q

What is the Parieto-Occipito-Temporal junction?

A

Parieto-Occipito-Temporal junction
- responsible for smooth pursuit or fixation of the eyes on a slow moving object
- signal originates IPSILATERAL to direction of smooth pursuit
- supply: Middle Cerebral Artery

20
Q

What is the Wallenberg Lateral Medullary Syndrome?

A
  • disorder due to damage to the lateral portion of the medulla
  • due to ischemia from an infarction in the:
    1. Posterior Inferior Cerebellar Artery
    + supplies the lateral medulla and inferior cerebellar peduncle
    + more common
    2. Vertebral Artery
    + supplies majority of the medulla

Symptoms:
1. Horner syndrome
- miosis + ptosis + reverse ptosis + anhidrosis
- due to disruption of the oculosympathetic pathway descending in the lateral medulla
2. Dizziness, nausea, vomiting, vertigo
- due to oscillopsia from rotary nystagmus
- disruption of communicating neurons between brainstem and inferior cerebellar peduncle
3. Binocular oblique diplopia
- due to skew deviation
- disruption of otolithic input at the brainstem
4. Gait ataxia
5. 3Ds: Dysphagia, Dysarthria, Dysphonia

21
Q

What is a Field of Vision?

A
  • portion of space in which objects are visible at the same time or moment during STEADY fixation of gaze in one direction
  • depicted as a 3D hill, with the peak sensitivity occurring at the central fixation point under photopic conditions, decreasing rapidly in the 10º around fixation, and then decreasing very gradually for locations further in the periphery
    + central: 20/20
    + periphery: movement discrimination
  • the visual field and the retinal fibers have an INVERTED and REVERSED relationship
    + NASAL retina = TEMPORAL field
    + TEMPORAL retina = NASAL field
    + SUPERIOR retina = INFERIOR field
    + INFERIOR retina = SUPERIOR field

MONOCULAR Visual Field

  • Horizontal gaze: 160 degrees total
    + temporal: 100 degrees
    + nasal: 60 degrees
  • Vertical gaze: 130 degrees total
    + superior: 60 degrees
    + inferior: 70 degrees
  1. Central: inner 30 degrees
    - bisected by a vertical line which divides the field into NASAL and TEMPORAL hemifields
  2. Peripheral: beyond 30 degrees

BINOCULAR Visual Field:

  • Horizontal gaze: 140 degrees total
    + temporal: 90 degrees
    + nasal: 50 degrees
  • Vertical gaze: 110 degrees total
    + superior: 50 degrees
    + inferior: 60 degrees
22
Q

What is a scotoma?

A
  • area of depressed or absent vision surrounded on all sides by relatively better vision
  • depression or absence of vision anywhere EXCEPT the anatomic blindspot is abnormal
23
Q

Where is the anatomic blindspot?

A

Optic Nerve Head
- corresponds to the posterior scleral foramen through which RNFL exit the eye via optic disc
- NO photoreceptors present, creating a NORMAL absolute scotoma
- located NASAL and SUPERIOR to fovea
- corresponding scotoma:
+ 10 - 15 degrees TEMPORAL to fovea
+ 1.5 degrees BELOW the horizontal raphe
- positive responses to stimuli at this spot are assumed to reflect loss of fixation

Pathology: Papilledema
- enlarged blindspot in perimetry

24
Q

How are the visual fields objectively tested?

A

Perimetry
- systematic and objective measurement of the visual field
- measures sensitivity to stimuli at multiple locations in the visual field
- require separate testing of right and left eyes

Standard Automated Perimetry
- White-on-White Perimetry
- most common form of visual field testing
- a white stimulus is projected on a white background to determine the threshold values

Types based on presentation of stimulus:
1. Kinetic: Goldmann
- stimulus is MOVING from a non-seeing area to a seeing area
- location where object is first seen is recorded

  1. Static: Humphrey, Octopus
    - STATIONARY stimuli are presented at defined points in the visual field
    - stimuli presented for longer durations of time may be seen better as a result of temporal summation of information

Note:
Humphrey 24-2
- extended partially to beyond 30 degrees nasally to detect NASAL STEP scotoma

25
Q

Discuss the three basic patterns of axon arrangement in the retinal nerve fiber layer.

A
  1. Papillomacular Bundle
    - NASAL ON fibers that originate from the macula and enter the optic nerve TEMPORALLY
    - > 90% of all RNF
    - for maintenance of sharp focus of central fixation
  2. Nasal Bundle
    - NASAL ON fibers that originate from the nasal retina and enter the optic nerve NASALLY
  3. Arcuate Bundle
    - TEMPORAL ON fibers that originate from the temporal retina and enter the optic nerve SUPERIORLY and INFERIORLY
    - located temporo-superiorly and temporo-inferiorly to the papillomacular bundle
26
Q

What is the Bjerrum’s Area?

A
  • central 25° of the visual field from the fixation point
  • 90% of the early glaucomatous changes were within this area
27
Q

What are the different Optic Nerve - type defects?

A
  • defects that originate from the blind spot
  • do NOT respect the VERTICAL meridian

Symptoms:
- decrease VA
- decreased color perception (esp. if involving the papillomacular bundle)
- (+) RAPD

Types:
1. Papillomacular bundle defects
2. Nasal bundle defects
3. Arcuate bundle defects

28
Q

What are the papillomacular bundle defects?

A
  • NASAL ON fibers that originate from the macula and enter the optic nerve TEMPORALLY

Examples:
1. Ethambutol-related Toxic Optic Neuropathy
2. Leber Hereditary Optic Neuropathy

Scotomas:
1. Central
- covers the central fixation point

  1. Cecocentral
    - central scotoma connected to the blindspot
  2. Paracentral
    - involves fibers adjacent to but NOT involving the central fixation point
29
Q

What are nasal bundle defects?

A
  • NASAL ON fibers that originate from the nasal retina and enter the optic nerve NASALLY
  • courses in a straight and radial fashion
  • do NOT necessarily respect the temporal horizontal meridian

Examples: Glaucoma

Scotoma: Wedge-shaped temporal scotoma

30
Q

What are arcuate bundle defects?

A
  • TEMPORAL ON fibers that originate from the temporal retina and enter the optic nerve SUPERIORLY and INFERIORLY
  • located temporo-superiorly and temporo-inferiorly to the papillomacular bundle

Examples:
1. Glaucoma
2. Non-Arteritic Ischemic Optic Neuropathy
3. Branch Retinal Artery/Vein Occlusion

Scotomas:
1. Seidel
- defect in the PROXIMAL portion of the nerve bundle
- comma-shaped extension of the blindspot

  1. Arcuate/Bjerrum/Scimitar
    - appears like an extension of Seidel scotoma
    - arcuate portion of the visual field around 15 degrees from central fixation
    - starts at the blindspot and ends as a horizontal line at the nasal field
    - respects the horizontal raphe
  2. Nasal Step of Roenne
    - localized defect in the nasal field involving the DISTAL portion of the nerve bundle
    - respects the horizontal raphe
  3. Altitudinal
    - involves the entire superior or inferior horizontal half of the visual field
    - respects the horizontal raphe
31
Q

Describe the prechiasmal defects.

A
  • respects the HORIZONTAL meridian
  • unilateral
  • associated defects:
    1. poor vision
    2. color perception deficits
    3. impaired contrast sensitivity
    4. (+) signs of optic neuropathy

Ddx:
1. Non-organic causes
- refractive errors
- media opacities
- retinal defects
- malingering
- hysteria

  1. Temporal Crescent Syndrome
    - organic POSTchiasmal defect
32
Q

What are the chiasmal defects?

A
  • presents with BILATERAL bow-tie optic atrophy or pallor
    + decussating NASAL ON fibers are affected
    + temporal aspect: papillomacular bundle
    + nasal aspect: nasal bundle

Causes:
1. Pituitary adenoma
2. Craniopharyngioma
3. Meningioma
4. ICA aneurysm

Scotomas:
1. Bitemporal Hemianopsia
2. Central Bitemporal Hemianopsia
3. Junctional Scotoma

33
Q

What is a Bitemporal Hemianopsia?

A
  • interruption of the decussating NASAL fibers
  • respects the VERTICAL midline
  • VA unaffected until later (temporal fibers still intact)

Remember: Chiasm
- inclined at a 45-degree angle
- anterior chiasm is more INFERIOR than posterior chiasm
- inferior nasal fibers cross first and anteriorly while superior nasal fibers cross last and posteriorly

Types based on location of lesion:
1. Suprachiasmatic: ICA aneurysm, Meningioma
- superior nasal fibers affected –> denser scotoma inferiorly
- prominent papilledema due to close proximity to 3rd ventricle

  1. Infrachiasmatic: Craniopharyngioma, Pituitary adenoma
    - inferior nasal fibers affected –> denser scotoma superiorly
34
Q

What is a Central Bitemporal Hemianopsia?

A
  • involves the bilateral temporal hemifields within the central fixation
  • respects the VERTICAL midline
  • due to a posterior chiasmal lesion
  • initially only affects the decussating macular fibers crossing most posterior in the chiasm
35
Q

What is a Junctional Scotoma?

A
  • lesion located at the Wilbrand’s Knee
    + junction of the optic nerve and the chiasm
    + inferonasal retinal fibers decussate in the chiasm but then travels anteriorly in the contralateral optic nerve before turning back to join the uncrossed inferotemporal fibers

Findings:
1. IPSILATERAL central scotoma
- involvement of the macular fibers of the ipsilateral eye prior to decussating

  1. CONTRALATERAL superotemporal scotoma
    - damage to the inferonasal fibers of the contralateral eye
36
Q

Describe the retrochiasmal defects.

A
  • presents with variants of CONTRALATERAL HOMONYMOUS HEMIANOPSIA
  • bilateral involvement: uncrossed temporal fibers of the ipsilateral eye + decussated nasal fibers of the contralateral eye
  • respects the VERTICAL meridian
  • NO decrease in VA and NO signs of optic neuropathy: fibers from both eyes are still present in the contralateral pathway

Causes:
1. Stroke: most common
2. Traumatic brain injury
3. Tumors

NOTE:
The more POSTERIOR the lesion, the more CONGRUOUS the defect
- similar in size, shape, depth and location
- nerve fibers of corresponding retinal area already lie adjacent to each other

37
Q

Describe the visual field defects in optic tract lesions.

A

INCONGRUOUS, INCOMPLETE, CONTRALATERAL, HOMONYMOUS HEMIANOPSIA
- nerve fibers of corresponding retinal points do NOT yet lie adjacent to each other

CONTRALATERAL RAPD
- each optic tract contains more pupillomotor input from the contralateral eye consisting primarily of the decussated nasal fibers (~ 53%)
- visual acuity and color perception are NOT affected because only the contralateral macular fibers are affected

OPTIC ATROPHY/PALLOR
1. CONTRALATERAL BOWTIE pattern: involvement of papillomacular and nasal fibers
2. IPSILATERAL TEMPORAL pattern: involvement of the arcuate fibers

Cause: Mass effect
1. Aneurysms
2. Tumors

38
Q

Describe the visual field defects in LGN lesions.

A

Review: SMILe
1. Antero-medial and antero-lateral LGN = ACA
2. Posterior LGN (hilum) = PLCA
3. Inferior field = Superior retina = Medial LGN
4. Superior field = Inferior retina = Lateral LGN

INCONGRUOUS or RELATIVELY CONGRUENT, INCOMPLETE CONTRALATERAL HOMONYMOUS SECTORANOPSIA
- wedge-shaped

  1. Quadruple Sectoranopia
    - one wedge-shaped defect in the most superior VF and another in the most inferior VF
    - lesions of anteromedial and anterolateral LGN
    - supply: Anterior Choroidal Artery (branch of the Middle Cerebral Artery)
  2. Horizontal Sectoranopia
    - two wedge-shaped defects which combined into one larger wedge in the middle
    - lesions of posterior LGN or hilum
    - supply: Posterolateral Choroidal Artery (branch of the Posterior Cerebral Artery)

NO RAPD
- retino-tectal tract involved in the pupillary light reflex has already exited anteriorly into the Brachium of the Superior Colliculus going to the pretectal nucleus and EW nucleus

CONTRALATERAL BOWTIE ON ATROPHY (?)

39
Q

Describe the visual field defects in optic radiation lesions.

A

Review: SMILe
1. INFERIOR field = Superior retina = Medial LGN = UPPER radiations = PARIETAL lobe

  1. SUPERIOR field = Inferior retina = Lateral LGN = LOWER radiations = TEMPORAL lobe

A. Parietal Lobe lesions
- CONTRALATERAL INFERIOR HOMONYMOUS QUADRANTANOPSIA
(Pie-in-the-FLOOR)
- cause: CVA
- associated symptoms:
1. CONTRALATERAL conjugate eye deviation (Wrong-Way Deviation): involvement of descending oculomotor pathways from the contralateral hemisphere at the midbrain level
2. IPSILATERAL smooth pursuit deficiency: damage to the ipsilateral POT-J
3. ASYMMETRIC optokinetic nystagmus (OKN)
4. Higher cortical dysfunctions
5. Spatial disorientation
6. Hemiparesis

Gerstmann Syndrome
- lesion in the DOMINANT parietal lobe
- tetrad:
1. Agraphia: inability to write
2. Acalculia: inability to calculate
3. Finger agnosia: inability to identify fingers
4. L-R confusion

B. Temporal Lobe lesions
- CONTRALATERAL SUPERIOR HOMONYMOUS QUADRANTANOPSIA
(Pie-in-the-SKY)
- cause: Tumors
- associated symptoms:
1. Hallucinations (Olfactory, Gustatory, Visual)
2. Seizures
3. Receptive/Wernicke aphasia

40
Q

Difference between Receptive and Expressive Aphasia.

A

Receptive/Fluent Aphasia
- Wernicke’s Aphasia
- POOR comprehension: cannot read or understand
- effortLESS speech
- meaningLESS sentences

Expressive/Non-Fluent Aphasia
- Broca’s Aphasia
- GOOD comprehension
- effortFUL speech
- meaningFUL sentences BUT inappropriate words

41
Q

What is the Cogan’s Dictum?

A

Mnemonic: PASO

Homonymous hemianopsia +
1. Asymmetric OKN = Parietal lesion = Mass
2. Symmetric OKN = Occipital lesion = Infarct

42
Q

Describe the visual field defects in occipital lobe lesions.

A
  • processes the CONTRALATERAL field
    + Left occipital lobe: Right visual field
    + Right occipital lobe: Left visual field
    + Anterior occipital lobe: temporal crescent
    + Posterior occipital lobe: peripheral field
    + Occipital tip: central field
  • usually ISOLATED: no other associated symptoms (vs temporal and parietal lesions)
  • 55 - 60% occupied by the MACULAR fibers
    + terminate in the occipital tip
    + watershed area: border between the vascular supply of the MCA and PCA (Calcarine artery)

COMPLETE CONGRUENT CONTRALATERAL HOMONYMOUS HEMIANOPSIA

A. Anterior Occipital lobe
- 8 - 10% of striate cortex
- Temporal Crescent defect: the only MONOcular peripheral defect

B. Posterior Occipital lobe
- Temporal Crescent-SPARING defect: homonymous hemianopsia with sparing of the contralateral temporal crescent

  1. Occipital tip NOT involved:
    - Macular-SPARING defect: sparing of at least 5 degrees of central vision
  2. Occipital tip ONLY:
    - Central defect: central and mid-peripheral homonymous hemianopsia

C. BOTH Anterior and Posterior Occipital lobe WITH Occipital tip
- Complete defect: complete homonymous hemianopsia

D. BILATERAL Occipital lobe lesion NOT involving the occipital tip
- Bilateral Homonymous Hemianopsia WITH macular-SPARING: bilateral constricted field

Remember:
1. BITEMPORAL central defects = CHIASM

43
Q

What is the Temporal Crescent Syndrome?

A
  • ONLY POSTchiasmal defect that do NOT present with contralateral homonymous hemianopsia
  • MONOcular crescent-shaped defect in the temporal/peripheral visual field CONTRALATERAL to the lesion
    + outermost 20 degrees
    + 30 - 40% of temporal vision
    + outside the scope of binocular vision (temporal VF > nasal VF)
    + served only by the ipsilateral nasal retina
  • localization: Antero-Medial Striate Cortex
    + contralateral to lesion
    + accounts for 8 - 10% of striate cortex
    + affects fibers of the NASAL retina serving the most peripheral/TEMPORAL visual field

Ophthalmology (44 decks)

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