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H+N - C > Vision 2 > Flashcards

Vision 2 Flashcards

1
Q

What are the two types of ocular muscles?

A

Intrinsic muscles:

  • Control pupil diameter
  • helps alter lens curvature
  • Enable us to see near objects

Extrinsic muscles:

  • Also called extra ocular muscles or EOMs)
  • Move the eye
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2
Q

What are the 4 straight and 2 oblique extrinsic ocular muscles that move the eye?

A

Straight muscles called recti:

  • Medial rectus
  • Lateral rectus
  • Inferior rectus
  • Superior rectus

Oblique muscles:

  • Superior Oblique
  • Inferior Oblique
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3
Q

Where do the extrinsic muscles of the eye arise from in the orbit?

A

The recti muscles arise from the apex of the orbit from an annular fibrous ring.

The superior oblique muscles arise from the roof of the orbit posteriorly

The inferior oblique muscles arise from the floor of the orbit anteriorly

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4
Q

What muscle closes the eyelid?

A

Levator Palpebrae Superioris

It lies just superiorly to the superior rectus muscle

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5
Q

Where do the extrinsic ocular muscles attach to the eye?

A

The recti muscles insert onto the sclera anteriorly

Obliques insert posteriorly

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6
Q

What is the origin and insertion of the Levator palpebrae superioris?

A

Origin: roof of orbit

Insertion: upper eyelid

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7
Q

What is the origin and insertion of all the recti muscles of the eye?

A

Origin: tendinous ring

Insertion: sclera posteriorly

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8
Q

What is the origin and insertion of the superior oblique muscle?

A

Origin: lesser wing of sphenoid

Insertion: Sclera posteriorly

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9
Q

What is the origin and insertion of the inferior oblique muscle?

A

Origin: medial part of orbit floor

Insertion: sclera posteriorly

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10
Q

Is the obicularis oculi an EOM?

A

No

Muscle of facial expression

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11
Q

What is the nerve supply to the extrinsic ocular muscles?

A

Trochlear (IV) nerve supplies muscle with trochlea (SO)
-Only muscle it supplies in the whole body

Abducent (VI) nerve supplies muscle which abducts (LR)

Everything else
-Oculomotor (III) nerve

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12
Q

The action of individual EOMs are influenced by 2 factors. What are they?

A

The muscles are attached along the orbital axis and not the optical axis, so they pull on the eyeball at an angle.
This is why the superior and inferior recti have more than 1 function.

The oblique muscles are attached to the posterior part of the sclera, so they pull the posterior part of the eyeball up/down and the anterior part moves in the OPPOSITE direction

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13
Q

How do you test the actions of EOMs?

A

The obliques elevate/depress when the eye is adducted.

The recti (SR and IR) elevate/depress when the eye is abducted

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14
Q

What is a sign of right third nerve palsy?

A

Drooping eyelid

Eye can move only laterally (and slightly down)

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15
Q

What is a sign of left fourth nerve palsy?

A

Eye moving up when adducted

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16
Q

What is a sign of Abducent (6th) nerve palsy?

A

Eye being adducted

Eye not able to abduct

17
Q

What is Strabismus?

A

Squint (misalignment of the eyes)

18
Q

What are the two types of Strabismus?

A

Esotropia (manifest convergent squint)

Exotropia (manifest divergent squint)

19
Q

What are the functional consequences of strabismus?

A

Amblyopia (lazy eye)

  • Where brain surpasses the image of one eye leading to poor vision in that eye without any pathology
  • Correctable in early years using eye patches to stimulate the “lazy” eye to work

Diplopia (double vision)
-Usually occurs in squints occurring as a result of nerve palsies

20
Q

What is a visual field?

A

Everything you see with one eye (including in the periphery) is your visual field.

Images of objects in your field of vision is formed in upside down and inverted on your retina

21
Q

Describe the visual pathway in depth up to the formation of the optic tract

A

All fibres from the eye pass through the optic nerve to the optic chiasma.

At the optic chiasma the (medial) nasal fibres cross to the opposite side.

So the optic tract contains fibres from the (lateral) temporal half of the ipsilateral eye and the crossed over nasal fibres from the contralateral eye.

This corresponds to ALL fibres from the opposite half of the visual field.

22
Q

Describe the visual pathway in depth from the formation of the optic tract

A

Fibres from the optic tract synapse at the lateral geniculate body of the thalamus.

From here the optic radiation passes behind the Internal Capsule (retro-lentiform fibres) to reach the Primary Visual Cortex in the Occipital lobe (Area 17)

Thus the right visual cortex sees the left half of the visual field and vice versa.

23
Q

Describe the visual pathway very basically

A

Image -> optic nerve -> optic chiasma -> optic tract -> lateral geniculate body of thalamus -> optic radiation -> visual cortex

24
Q

What symptom/sign would someone have if their right optic nerve was damaged?

A

Blindness in one eye

25
Q

What symptom/sign should someone have if they had their optic chiasma damaged in the middle

A

Bitemporal hemianopia

Only lateral field of vision

26
Q

What symptom/sign would someone have if their right optic tract is damaged?

A

Contralateral Homonymous Hemianopia

Left field of vision missing

27
Q

What symptom/ sign would someone have if their optic radiation is damaged?

A

Contralateral Homonymous Hemianopia

Contralateral field of vision missing.
Same as optic tract damage

28
Q

What are the intrinsic eye muscles?

A

Ciliaris muscle: in ciliary body

Constrictor pupillae: in iris at pupillary border

Dilator pupillae: radially running muscle in iris

29
Q

What is the innervation of the intrinsic eye muscles?

A

Ciliaris muscle and Constrictor papillae by parasympathetic (IIIn)

Dilator papillae by sympathetic (plexus around blood vessels

30
Q

What does pathology of innervation of intrinsic muscles lead to?

A

Pupillary abnormalities

31
Q

What is the effect of increased illumination and decreased illumination in pupillary reaction?

A

Increased illumination -> parasympathetic -> both pupils constrict

Decreased illumination -> sympathetic -> pupils dilate

32
Q

How do you elicit the pupillary reflex?

A

Start in a dimly lit room (pupils dilated)

Pen torch in front of one eye -> check for both pupils constricting (direct and consensual reflex)

Swing light to other side -> should remain both pupils constricted

33
Q

What is the pathway of the light reflex? (Afferent limb)

A

When light falls on the retina, impulses travel along the optic nerve -> optic chiasma -> optic tract

Fibres destined to activate the pupillary relfex do not go to the LGB.
Instead they leave the optic tract to go to the midbrain (where the IIIn nucleus is situated)

Part of the IIIn nucleus is the Edinger-Westphal nucleus (EWN) for parasympathetic fibres. The papillary-reflex-fibres go to EWN of BOTH SIDES!!!1!

34
Q

What is the pathway of the light reflex? (efferent limb)

A

From EWN (part of IIIn nucleus)

Preganglionic parasympathetic pass through IIIn into orbit. (come out with optic nerve)

Parasympathetic fibres go to and synapse in ciliary ganglion

Postganglionic fibres go through short ciliary nerves to constrictor papillae

Pupillary constriction of both sides.

35
Q

Give some pupil abnormalities

A

Pupils maybe of different sizes = aniscocoria
-e.g. Horner’s syndrome

Pupils may look normal but react abnormally to light (abnormal light reflex)

36
Q

What are some common causes of absent/abnormal pupillary reflex?

A

Any abnormality of the afferent limb/ centre/ efferent limb of the reflex

  • Diseases of the retina (detachment/degenerations or dystrophies)
  • Diseases of the optic nerve (such as optic neuritis (frequently seen in MS)
  • Diseases of the III cranial nerve (efferent limb)
37
Q

What should you check in a patient with IIIn palsy?

A

In IIIn palsy due to a medical cause such as diabetes, there is usually no damage to parasympathetic fibres.

So if you see a patient with a IIIn palsy, check pupillary

Reflex -> if absent -> suspect a cerebral artery aneurysm -> emergency

38
Q

What should you remember about sympathetic innervation and the eye?

A

Thoracolumbar outflow

Sympathetic chain and cervical ganglia

In the head and neck- postganglionic sympathetic fibres travel along with blood vessels

Horner’s syndrome can occur due to disruption at any point.
An example would be Pancoast’s tumour of the lungs

39
Q

What are the sign’s of hornet’s syndrome?

A

Ptosis, Miosis, Anhidrosis

Ptosis = drooping of eyelid on affected side
Miosis = constriction of pupil on affected side
Anhidrosis = loss of sweating on affected side

Anisocoria due to damage to the sympathetic innervation to the pupil

H+N - C (17 decks)

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