5 - The Eye

Question 1

What are the two layers of the retina?

Answer 1

Pigmented Layer: retinal pigment epithelium. contains lots of melanin to ensure no excessive refraction of light rays and stop glare. (albinos don’t have melanin so this is why they struggle with normal light being too bright)

Neural Layer: contains photoreceptors (rods and cones) and horizontal cells which do lateral inhibition that stops neighbouring cells to the highest intensity cells from detecting the light. Bipolar cells are found between photoreceptors and ganglion cells

Question 2

What is the blood supply to the retina?

Answer 2

• Comes from the choroid later from the central retinal artery
• Can get occluded due to atherosclerosis of the ICA

Question 3

How can we image the retina?

Answer 3

Optical Coherence Tomography

Question 4

What are some pathological processes that can affect the retina?

Answer 4

• Hypertension and diabetes can cause retinopathy
• Amaurosis Fugax in a stroke
• Macula degeneration
• Papilloedema in raised ICP

Question 5

What is Amaurosis Fugax?

Answer 5

- Transient monocular blindness

• CURTAIN COMING DOWN OVER VISION - THINK STROKE
• Due to blockage in ICA or retinal artery

Question 6

What are the components of the visual pathway and draw a diagram displaying the pathway?

Answer 6

Optic Nerve –> Optic Chiasm –> Optic Tracts –> Lateral Geniculate Nucleus in the Thalamus –> Radiations (superior and inferior) –> Occipital Lobe (primary visual cortex)

Question 7

What fibres are in the left superior radiation (Baum’s loop)?

Answer 7

• Left superior temporal fibre and right superior nasal fibre
• If in upper quadrant, in superior radiation and vice versa with lower quadrant

Question 8

Where are each of the radiations?

Answer 8

Superior: parietal lobe

Inferior: temporal lobe

Question 9

What fibres make up the optic nerve and what part of the visual field does each fibre contribute to?

Answer 9

- Nasal retinal fibres responsible for temporal visual field

- Temporal retinal fibres responsible for nasal visual field

• Due to the fact light travels in straight lines
• 4 fibres make up the nerve (superior and inferior)

Question 10

What is the difference between temporal and nasal fibres?

Answer 10

Question 11

Where are the optic tracts?

Answer 11

After the optic chiasm up to the lateral geniculate nucleus

Question 12

What is the best way to figure out where a lesion is in the visual pathway?

Answer 12

Visual field defects are names on area of visual loss not the lesion so draw the diagram out!!!

Question 13

What is monocular blindness and where is the lesion in this case?

Answer 13

- Complete vision loss in on eye

• Can be due to retinoblastoma, meningiomas or blockage in central retinal artery (stroke)

- Lesion in optic nerve so ipsilateral temporal and nasal fibres lost

Question 14

What type of visual field loss is this, and where is the lesion in the visual pathway?

Answer 14

Bitemporal Hemianopia

- Lesion in optic chiasm

• Loss of nasal fibres on both sides so you lose your temporal visual field, causing tunnel vision
• Pituitary gland tumour or anterior communicating artery aneurysm

Question 15

What type of visual field loss is this, and where is the lesion in the visual pathway?

Answer 15

Left homonymous hemianopia

- Lesion in the right optic tract. Contralateral lesion to vision loss, use nasal field loss to guide side of lesion as temporal fibres don’t decussate

• Could be neoplasia or trauma

Question 16

What part of the visual field do the optic radiations supply?

Answer 16

• Inferior radiations supply superior visual vield and vice versa

Question 17

What type of visual field loss is this and where is the lesion?

Answer 17

- Left homonymous inferior quadrantanopia

- Lesion in right superior optic radiation (parietal lobe)

Question 18

What type of visual field loss is this and where is the lesion?

Answer 18

Right superior homonymous quandrantanopia

• Left inferior radiation lesion

Question 19

Apart from a lesion in the optic tract, what other pathology could result in a homonymous hemianopia?

Answer 19

A stroke affecting the MCA could knock out both radiations ipsilaterally, have to look at the clinical history to distinguish between stroke and damage to a tract

Question 20

What are these visual field defects showing and why does this occur?

Answer 20

- Macular Sparing: still good central vision

• Occipital lobe has dual blood supply from PCA and MCA.
• If there is a stroke of the PCA, most of the occipital lobe is lost but the MCA supplies the occipital pole(macula) so vision is spared centally

Question 21

Draw the nerve pathway involved in the light reflex.

Answer 21

• Light stimulates CNII and goes on to synaps with Edinger Westphal nucleus in pre tectal area
• Parasympathetic respone through efferent CNIII
• Direct and consensual pupil constriction via constricter pupillae

Question 22

Draw the nerve pathway involved in the accomodation reflex.

Answer 22

3 C’s:

• Convergence (medial rectus)
• Constriction (constrictor pupillae)
• Convexivity so fat lens (cilliary muscles)

Cerebral cortex involved as well as midbrain as some image interpretation unlike in the light reflex. Occipital lobe sends fibres back up to midbrain

Question 23

Label the cranial nerves on this cadaveric specimen.

Answer 23

Question 24

Where does the fundus sit in relation to the optic disc?

Answer 24

Lateral

Question 25

What visual field loss occurs in a lesion of the following: - Optic Nerve - Optic Chiasm - Optic Tract - LGN - Optic radiations

Answer 25

- Damage to the optic nerve can lead to monocular blindness - Damage to the medial chiasm causes bitemporal hemianopia - Damage to the optic tract causes a contralateral homonymous hemianopia - Damage to the lateral geniculate causes a contralateral homonymoushemianopia - Damage to both optic radiations causes a contralateral homonymous hemianopia

Question 26

What is a scotoma?

Answer 26

A localised defect in the retina can cause a small patch of visual loss which can form an aura in the vision (google)

Question 27

What visual field loss is in the following situations: - Non vascular damage to occipital lobe - Occlusion of PCA - Damage to superior optic radiations - Damage to inferior optic radiations

Answer 27

- Non vascular damage to the occipital lobe can cause a contralateral homonymous hemianopia without macular sparing - Occlusion of the posterior cerebral artery causes a contralateral homonymous hemianopia with macular sparing due to deep branch MCA - Damage to the superior optic radiations (in the parietal lobe) causes contralateral homonymous inferior quadrantanopia - Damage to the inferior optic radiations (in the temporal lobe) causescontralateral homonymous superior quadrantanopia

Question 28

What is the way to remember what to test in a neurological exam?

Answer 28

The Power Rangers Can't Stand Show Tunes

Question 29

What tuning fork should you use for joint vibration?

Answer 29

128 Hz (256 is for Rinne's)

Question 30

What is the MRC power scale?

Answer 30

Question 31

What are some signs of cerebellar disease/lesions?

Answer 31

Question 32

Why do patient's with albinism struggle to see well in bright light?

Answer 32

They have less pigment in their lens so more light gets through and onto the retina. Retinal epithelium has more damage as no pigment to absorb free radicals and excess light rays so glare Can also get glare in cataracts, presbyopia, short/long sighted, astigmatism

Question 33

Label the layers of the retina on this OCT.

Answer 33

- Vitreous is top black bit - Choroid is bottom black bit

Question 34

Following a stroke in her left hemisphere, a patient is finding that she keeps bumping into the wall on her right side, what is this visual field loss called and where in the visual pathway is the lesion?

Answer 34

**- Right homonymous hemianopia** - Stroke knocked out both optic radiations in the left in the parietal and temporal lobe

Question 35

How can we determine whether a homonymous hemianopia following a stroke is due to a lesion in the optic tracts or the visual cortex?

Answer 35

If in the visual cortex there will be **macular sparing** as a stroke is a vascular event and the PCA supplies the macular area of the visual cortex

Question 36

What are some differentials for this case and where is the most likely site of the lesion?

Answer 36

- Abscess from meningitis - Subarachnoid haemorraghe - Left superior radiation so abscess in the parietal lobe (TIPS)

Question 37

What is the doll's eye reflex?

Answer 37

- Way to test the oculocephalic reflex as one test for brain stem death. Show when loss of connections between vestibular and occulomotor - Move head to the side quickly and eyes should attempt to go back to midline position if connections in tact.

Question 38

What is the medial longitudinal fasiculus?

Answer 38

- Midline area in the brain stem that connects **occulomotor, trochlear and abducens** nuclei for **conjugate eye movements** - Also a connection with the vestibular nuclei to give information about the position of the head. Vestibular also give out descending fibres to muscles of the head and neck - Stops us getting **diplopia**

Question 39

What is internuclear ophthalmoplegia and the main cause of this?

Answer 39

- Often seen in MS when a new plaque from demyelination occurs in the brain stem. DIPLOPIA - Loss of conjugate lateral eye movements with affected eye struggling to adduct slowly or absent - When an attempt is made to gaze contralaterally (relative to the affected eye), the affected eye adducts minimally, if at all. The contralateral eye abducts, however with nystagmus

Question 40

A patient has a cerebral aqueduct tumour in the midbrain. How will this affect the accomodation reflex and eye movements?

Answer 40

- Tumour will compress **EDW and occulomotor nerve** - EDW damage will ean lack of pupil constriction and ciliary muscle contraction - Damage to occulomotor nerve means eye held in down and out position

Question 41

What artery is normally blocked in amaurosis fugax?

Answer 41

Central retinal artery

Question 42

What are thalamoperforator arteries a branch of?

Answer 42

PCA!!!!

Question 43

A patient has a tumour arising from the right cavernous sinus invading medially towards the optic chism, what visual field defect might this result in?

Answer 43

Right Nasal Hemianopia