Unit 14 Week 1

Question 1

Key discussino topics

Answer 1

• Anatomy of the eye
• Retina: photoreceptors and retinal ganglion cells
• Not horizontal, bipolar and amacrin cells
• Basis of blind spot
• Vitreous and aqeueous humors (increased intraocular pressure and impaired drainage)
• Cranial nerves relevant to visual system, including testing
• Reflexes- accommodation, red, pupilliary
• Occulomotor movements of the eye; innervatio nof muscles, common palsies
• Basics of phototransduction: rhodopsin reacts to photon, hyperpolarises cell, reducing neurotransmitter release (Sensory cells usually release more when stimulated)– cells/ neural pathways are more important than molecular process
• Colour vision: distribution and roles of Rods, Cones− Detailed knowledge of colour blindness is not needed
• Visual acuity, including testing and correcting with lenses
• Visual Fields mapping to Retina and Neural Pathways (stop at cortex)− Know that there is Retinotopic mapping in cortex; do not need details
• Identify and explain common deficits: ptosis, diplopia…
• Discuss how stigma may affect diagnosis and treatment
• Communication across a sensory barrier (e.g. visually impaired people)

Question 2

What is myopia

and what lens would correct it

Answer 2

• nearsightedness
• the point of focus is in front of the retina because the cornea is too steeply curved
• the axial length of the eye is too long, or both
• Distant objects are blurred, but near objects can be seen clearly

fix with a concave (minus) lens

Question 3

What is hyperopia

and what lens would correct it

Answer 3

• farsightedness)
• the point of focus is behind the retina because the cornea is too flatly curved, the axial length is too short or both
• In adults both near and distant objects are blurred
• Children and young adults with mild hyperopia may be able to see clearly because of their ability to accommodate

To correct hyperopia, a convex (plus) lens is used

Question 5

What is astigmatism

what lens would you use to fix it

Answer 5

nonspherical (variable) curvature of the cornea or lens causes light rays of different orientations (eg, vertical, oblique, horizontal) to focus at different points

To correct astigmatism, a cylindrical lens (a segment cut from a cylinder) is used

Cylindrical lenses have no refractive power along one axis and are concave or convex along the other axis

Question 6

What is presbyopia

when in your life would you develop it

what lens would you use to fix it

Answer 6

loss of the lens’ ability to change shape to focus on near objects due to aging

Typically, presbyopia becomes noticeable by the time a person reaches the early or mid 40s

A convex (plus) lens is used for correction when viewing near objects

Question 7

What is Anisometropia

Answer 7

significant difference between the refractive errors of the 2 eyes

Question 8

In adults most double visino is caused by:

Answer 8

▪ Squint (strabismus),

due to:

1. Neurological (paresis of III, IV or VI)
2. Muscular (weakness, paralysis; e.g. myasthenia gravis) dysfunction
3. Mechanical restriction (e.g. tumour)

Question 9

What causes eye ache

Answer 9

optic neuritis

nflammation affecting nerve function, in this case due to MS episodes

Question 10

What part of the orbit is the lacrimal gland found

which cranial nerve innervates it

Answer 10

anterolateral aspect of the orbit

innervated by the facial nerve

Question 11

Ectropion

Answer 11

eyelid turned out

usually due to ageing (chronic scarring/ inflammation) or VII palsy

Question 12

Entropion

Answer 12

inturned eyelid

Question 13

Which muscle holds upper eyelid open?

What is it called when the upper eyelid droops?

What are 2 causes

Answer 13

levator muscle, symp innervation by CN III

ptosis

1) CNIII plasy
2) Horner’s syndrome (miosis- constricting of pupil, ptosis and anhidrosis)

Question 14

What is visual acuity

what does it depend on

what clinical tool do you use to measure it

Answer 14

Visual acuity refers to ability of each eye to ‘see’ fine detail; essentially, the ability to distinguish two points as separate.

Depends on numerous factors:

• Density of photoreceptors
• Degree of convergence of outputs from photoreceptors
• Object illumination
• Pupil diameter

Snellen chart

Question 15

What is the pinhole test

Answer 15

blocks most light that would be refracted, limiting to centre of cornea/ lens/ retina

If blur reduced, suggests a refractive error

Question 16

Internuclear opthalmoplegia

Answer 16

in MS, demyelination commonly affects medial longitudinal fasciculus (MLF) in brain stem, which coordinates eye movement

Stops rectus muscles contracting effectively, so eyes do not move in tune with each other, producing double vision (can also occur in stroke and myasthenia gravis)

can also be caused by CN III palsy or CN VI (abducent)

Question 17

What is RAPD

Answer 17

aka Marcus Gunn pupil

asymmetry of the pupillomotor input between the two eyes

detected by alternating the light from one eye to the other (swinging torch/flashlight test) and comparing the direct light reactions

Can detect unilateral disease of retina/optic nerve(but only anterior to optic chiasm)

Both pupils dilate when light on(affected) eye

Normal: pupil should constrict or stay the same size when the light is transferred to it from the other sideIf the pupil dilates when the light is shone on it, the light reflex is weaker than the consensual reflex, suggesting pathology of the optic nerve

Question 19

What would you see down a fundoscopy test

Answer 19

Question 20

What does the optic disc represent and how does it link to the blind spot

Answer 20

Output from the eye is via the Retinal Ganglion Cells, whose axons form the optic nerve (II).

No photoreceptors present, photons landing on it aren’t detectable- natural blindspot

Question 21

1. What are the 2 main classes of photreceptor?
2. What does each facilitate?
3. What part of the eye has a high conc of cones?
4. How many different kinds of cone are there?

Answer 21

1. Cones and rods
2. Cones- vision in high illumination and colour vision Rods- vision in low illumination
3. Cones are highest in the fovea, where visual acuity is greatest
4. 3 types of cone, each responding optimally to different wavelengths of light (red, green and blue)

Question 22

cataract

Answer 22

loss of lens clarity due to breakdown of proteins in the lens

Affects almost everyone >70

associated with corticosteroid use and diabetes

Question 23

Retinal detachment

Answer 23

• Neurosensory layer (photoreceptors + ganglion cells) detaches from retinal pigment epithelium as non replenishable vitreous fluid degenerates
• Usually a tear (ageing, trauma) allows liquid in between
• May see ‘floaters’ and ‘flashing lights’ due to vitreous degeneration
• If near macula, surgery is required

Question 24

Glaucoma

Answer 24

• various disorders, usually with raised intraocular pressure
• Aqueous humour overproduction or impaired drainage can increase pressure on vitreous humour, which presses on retinal nerves and blood vessels
• Can cause pain, loss of vision etc.

Question 25

What does “the visual cortex has retinotopic mapping” mean

Answer 25

we know which parts of the retina and the visual cortex handle specific areas of the visual field

Question 26

effect of midbrain on pupil size

Answer 26

Projections from optic tracts to midbrain control (direct and indirect) pupillary reflexes (illuminating one eye, shouldconstrict pupils in both eyes), as well as eye movements, and integrate visualand auditory information

Question 27

2 types of MRI view???? what are their relative benefits

Answer 27

T1: images reveal anatomical features more clearly, reverse is true, though fat is high signal on both. Gadolinium can be used as a contrast agent on T1 weighted images, showing increased perfusion (increased signal)

T2: images reveal pathological features more clearly high signal intensities from water, haematoma, tumours, inflammation, oedema, protein rich fluid; low signal intensities from cortical bone and muscle.

Question 28

At what vertebral level should you do a lumbar puncture

Answer 28

below the conus medullaris in the spinal cord;

normally below L2, usually between L4-L5 (Needle inserted into lumbar subarachnoid space)

Question 29

oligoclonal bands (electrophoresis?)

Answer 29

Oligoclonal bands: an increased number of immunoglobulin types, present in CSF of vast majority (~90%) of people with MSThis finding is highly specific, whereas a monoclonal (single) band is not

Question 30

Which cell type myelinates axons in the central nervous system?

Answer 30

oligodendrocytes

Question 31

2 drugs you may use in MS

Answer 31

prednisolone and B-interferon

Question 32

B interferon

Answer 32

an antiviral polypeptide, used for immunomodulatory therapy

Its mechanism of action in MS is not fully understood; it may reduce antigen presentation and T-cell proliferation

MS is characterised by multiple demyelinating episodes and usually affects multiple nerves

Question 33

What is visual evoked potential

Answer 33

visual stimulus presented, electrodes over occipital lobe detect cortical responses

Conduction time (latency) compared left v right, and normal-for-age values

Question 34

prosopagnosia

Answer 34

Loss of facial recognition due to brain damage

Question 35

What is bottom up processing

Answer 35

Bottom up processing starts with simple retinal processing,and builds increasingly complex interpretations as corticalbrain regions become involved, and as individual pieces ofinformation (e.g. edges, colours, movement) are combinedinto coherent images

Question 36

What is top down processing

Answer 36

• uses context or past experience to create a hypothesis about what we see
• The brain ‘likes to take shortcuts’, so expectation/anticipation pushes brain to ‘jump to conclusions’
• Humans expect faces, and see them everywhere