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Semester II - GHD > Vision > Flashcards

Vision Flashcards

1
Q

What’s the Fibrous coat of the eyeball composed of?

A
  • Cornea:
    + Anterior 1/6 which is transparent & allows light rays to enter the eyeball
    + Main refractive medium in the eye - 2/3 of the “power” of the eye
  • Sclera:
    + Opaque posterior 5/6 gives attachment to muscles moving eyeball
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2
Q

What’s the Vascular coat of the eye composed of?

A
  • Iris:
    + Controls diameter of the pupil and controls the amount of light rays entering the eyeball
  • Ciliary body:
    + Suspends the lens & produces AQUEOUS HUMOR
  • Choroid:
    + Supplies blood to outer layers of retina
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3
Q

What’s the Sensory coat of the eye composed of?

A
  • Retina:

+ Light sensitive rods and cones which enables us to see

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4
Q

When viewing the eye through a Ophthalmoscope, why does it appear orangey-red?

A
  • Choroid vascularity
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5
Q

How can you identify arteries via an Ophthalmoscope?

A
  • The are typically round and shiny
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6
Q

What’s the Fovea Centralis?

A

The area of the retina packed with cones, so maximum visual acuity

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7
Q

What’s the significance of the Optic Disc?

A

Start of the optic nerve = physiological blind spot

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8
Q

What are the features of the lens?

A
  • Transparent, crystalline biconvex structure which can change shape (becomes more or less convex)
  • Avascular - but this predisposes it to becoming opaque later in life (CATARACT)
  • Suspended in place by ZONULES which suspend from the ciliary body
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9
Q

What role does the Aqueous humor have?

A
  • Water fluid anterior to the lens which helps maintain intraocular pressure
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10
Q

What’s it called when Aqueous humor levels are low?

A

Hypotony

  • corneal decompensation, accelerated cataract formation, maculopathy, and discomfort
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11
Q

What’s the role does Vitreous humor have?

A
  • Transparent gel posterior to the lens & helps cushion the retina
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12
Q

Explain the dynamics of Aqueous Humor?

A
  1. Produced by Ciliary body in the space behind the iris and in from of the lens
  2. It flows out through the pupil to the space in front of the iris and behind the cornea
  3. Gets absorbed by a “filter” the trabecular meshwork which lies in the angle of the AC
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13
Q

How far does hthe Conjunctiva run?

A

Conjunctiva is a thin vascular membrane that covers the inner surface of eyelids and loops back over the sclera

BUT

Doesn’t cover the cornea

  1. Palpebral (tarsal) conjunctiva
  2. Fornical conjunctiva
  3. Ocular conjunctiva
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14
Q

What’s Conjunctivitis?

A

Inflammation of the conjunctiva

Doesn’t actually effect vision

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15
Q

How is the eye and nose connect?

A

The Lacrimal Apparatus - Nasolacrimal duct which passes into the inferior meatus of the nasal cavity

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16
Q

What’s the Lacrimal apparatus?

A

Lacrimal Gland:
- Situated in the orbit laterally + innervated by FACIAL NERVE (CN VII)

  • Lacrimal gland opens into the conjunctival sac
  • During each blink, conjunctival sac secretions (tears) are spread evenly on the surface of the cornea by the eye-lids
  • Tears drain through punctae on the medial side of each eyelid
  • Drains into the lacrimal sac which sits over the lacrimal bone
  • This drains through nasolacrimal duct into the inferior meatus of nasal cavity
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17
Q

What do the Intrinsic ocular muscles do?

A
  • Control pupil diameter and help alter lens curvature to enable us to see near objects
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18
Q

What do the Extrinsic ocular muscles do?

A
  • Move the eye

- Also called EXTRAOCULAR MUSCLE/EOMs

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19
Q

What are the 3 Intrinsic eye muscles (1)?

A

Ciliary: Constricts the ciliary body, relaxes tension on lens = lens becomes more round

Location: Muscle fibres in the ciliary body

Innervation: Parasympathetics from Oculomotor nerve (CNIII)

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20
Q

What are the 3 Intrinsic eye muscles (2)?

A

Sphincter/constrictor pupillae: Contraction of fibres decreases or constricts pupillary opening

Location: Circularly arranged fibres in the iris

Innervation: Parasympathetics from Oculomotor nerve (CNIII)

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21
Q

What are the 3 Intrinsic eye muscles (3)?

A

Dilator pupillae: Dilates the pupil

Location: Radially arranged fibres in the iris

Innervation: Sympathetics from the superior cervical ganglion (T1)

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22
Q

What are the extrinsic muscles of he eyeball?

A

= Extra-ocular muscles are involved in movements of the eyeball or raising upper eyelids

  1. Levator Palpebrae Superioris
  2. Superior Rectus
  3. Inferior Rectus
  4. Medial Rectus
  5. Lateral Rectus
  6. Superior Oblique
  7. Inferior Oblique
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23
Q

Where do the Rectus muscles originate from?

A

The common tendinous ring

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24
Q

Which muscle elevates the upper eyelid?

A

Levator palpebrae superioris (LPS):

Origin: Inferior surface of Lesser wing of sphenoid, anterior to optic canal

Insertion: Anterior surface of tarsal plate

Innervation: Oculomotor nerve (CNIII) - Superior branch

Function: Eyelid elevation

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25
Q

What’s the Superior Rectus?

A

Origin: Superior part of the common tendinous ring

Insertion: Anterior half of the eyeball superiorly

Innervation: Oculomotor nerve (CNIII) Superior branch

Function: Elevation, adduction, medial rotation of eyeball

26
Q

What’s the Inferior Rectus?

A

Origin: Inferior part of common tendinous ring

Insertion: Anterior half of eyeball inferiorly

Innervation: Oculomotor nerve (CNIII) Inferior branch

Function: Depression, adduction, lateral rotation of eyeball

27
Q

What’s the Medial Rectus?

A

Origin: Medial part of the common tendinous ring

Insertion: Anterior half of the eyeball medially

Innervation: Oculomotor nerve (CNIII) inferior branch

Function: Adduction of eyeball

28
Q

What’s the Lateral Rectus?

A

Origin: Lateral part of common tendinous ring

Insertion: Anterior half of the eyeball laterally

Innervation: Abducent nerve (CNVI)

Function: Abduction of eyeball

29
Q

What’s the Superior Oblique muscle?

A

Origin: Body of sphenoid, superior and medial to optic canal

Insertion: Outer posterior quadrant of eyeball (superior surface)

Innervation: Trochlear Nerve (CN IV)

Function: Depression, abduction, medial rotation of eyeball

30
Q

What’s the Inferior Oblique muscle?

A

Origin: Medial floor of orbit posterior to rim; maxilla lateral to nasolacrimal groove

Insertion: Outer posterior quadrant of eyeball (inferior surface)

Innervation: Oculomotor nerve (CNIII) Inferior branch

Function: Elevation, abduction, lateral rotation of eyeball

31
Q

Eye Movements: What’s Abduction?

A

Looking outwards (away from midline)

32
Q

Eye Movements: What’s Adduction?

A

Looking towards nose (to midline)

33
Q

Eye Movements: What’s Elevation?

A

Looking up

34
Q

Eye Movements: What’s Depression?

A

Looking down

35
Q

How does the Trigeminal Nerve supply the orbit/eyeball?

A

Ophthalmic division of the trigeminal nerve

  • Leaves trigeminal ganglion and passes forward in the lateral wall of the cavernous sinus inferior to the IV _ III nerves
  • Before it enters the orbit it branches into nasociliary, lacrimal and frontal nerves = enter orbit through Superior Orbital Fissure
  • Frontal + Lacrimal branches outside Common Tendinous ring
  • Nasociliary nerve within Common Tendinous Ring
36
Q

What are the 3 sub-divisions of the Ophthalmic nerve (1)?

A

Lacrimal Branch:

  • Smallest branch
  • Passes along upper border of lateral rectus muscle
  • Supplies lacimal gland, Conjunctiva and lateral part of upper eyelid
37
Q

What are the 3 sub-divisions of the Ophthalmic nerve (2)?

A

Frontal Branch:

  • Largest branch
  • Receives sensory input from areas outside the orbit
  • Exiting superior orbital fissure, passes forward between the LPS and the periorbita on the roof of the orbit
  • Midway across orbit it divides into: Supra-orbital and Supratrochlear nerve
38
Q

What’s the Supratrochlear Nerve?

A

Passes above trochlea and exits the orbit medial to the supra-orbital foramen and supplies the conjunctiva and skin of upper eyelid and skin on lower medial part of forehead

39
Q

What’s the Supra-orbital Nerve?

A

Passes between LPS and the periorbita covering he roof of the orbit - exits through supra-orbital notch and ascends across forehead + scalp - supplying eyelid and conjunctiva, forehead

40
Q

What are the 3 sub-divisions of the Ophthalmic nerve (3)?

A

Goes medially and its branches supply medial part of orbit, ethmoidal air sinus and nasal cavity

41
Q

What’s the Ciliary Ganglion?

A
  • Parasympathetic ganglion of Oculomotor nerve (CNIII)
  • Associated with nasociliary branch of Ophthalmic nerve (V1) + site where preganglionic and postganglionic parasympathetic neurons synapse as fibres from this part of autonomic division of PNS make their way to eyeball
  • Posterior part of orbit immediately lateral to optic nerve + between optic nerve and lateral rectus muscle
42
Q

What’s the arterial supply to the structures in the orbit including eyeball?

A

Ophthalmic Artery

43
Q

What’s the Ophthalmic artery?

A
  • Large branch given off by Internal Carotid Artery - given off immediately after internal carotid artery leaves the cavernous sinus
  • Passes into orbit through optic canal with optic nerve
44
Q

What branches from the Ophthalmic artery?

A

Central Retinal Artery:
- Enters optic nerve and proceeds down centre of nerve to retina - seen when viewing retina with an ophthalmoscope

Lacrimal Artery:
- Lateral side of optic nerve and passes anteriorly on the lateral side of the orbit - supplying lacrimal gland + lateral sides of eyelid

45
Q

What’s the visual pathway?

A
  1. Optic nerves pass to the Optic Chiasma
  2. At the Chiasma, the medial nasal fibres cross to the opposite side
  3. Optic tract contains fibres from the lateral temporal half of the ipsilateral eye and the crossed over nasal fibres from the contralaterlal eye
  4. Fibres from the optic tract synapse at the Lateral Geniculate Body (LGB) of the thalamus
  5. Optic radiation passes behind he internal capsule (retro-lentiform fibres) to reach the Primary Visual Cortex in the Occipital lobe (Area 17)
  6. The right visual cortex sees the left half of the visual field and vice-versa
46
Q

What happens if the Right Optic nerve is damaged?

A

Blindness in the left eye

47
Q

What happens if the Optic Chiasma is disrupted in the middle?

A

Bilateral hemianopia (blindness over half the field of vision)

48
Q

What happens if the Right Optic tract is damaged?

A

Contralateral homonymous hemianopia - blindness of the left side of visual field for both eyes

49
Q

What happens if Optic Radiation is damaged?

A

Contralateral homonymous hemianopia

50
Q

What’s Accommodation?

A
  • Changes that occur in both eyes as it changes focus form a distance to a close object
51
Q

What 3 factors comprise accommodation?

A
  1. Lens changes shape (becomes thicker & more spherical)
  2. Pupil constricts
  3. Eyes converge
52
Q

Why do lens change shape?

A
  • You need to get divergent light rays bent more to hit the retina as when they are far away only parallel rays hit the retina
    1. Ciliary body contraction (parasympathetic) causes ciliary body to bulge + suspensory ligaments become lax
    2. Lens becomes more spherical and thicker
53
Q

What’s Pupil constriction in Accommodation?

A
  • Looking at things up close we need a sharp focus
    1. Pupils constrict to allow only a few rays (those of the object) to pass through
    2. Pupillary constrictor is a concentric muscle around the border of the pupil which gets parasympathetic innervation from Trigeminal
54
Q

What’s Eye Convergence in Accommodation?

A
  • When focussing on an object up close, our eyes have to turn in to look at the object = convergence
  • Use medial rectus muscle of both eye to converge = medial muscle is larger than lateral
55
Q

What’s Myopia?

A

Short sightedness = image forms in front of the retina

56
Q

What’s Hyperopia?

A

Long sightedness = image forms behind the retina

57
Q

What’s Astigmatism?

A

Non-spherical curvature of cornea or lens

58
Q

What’s Presbyopia?

A

Long sightedness of old age = lens becomes rigid and cannot accommodate

59
Q

What’s the purpose of contact lenses/laser eye surgery/spectacle?

A

Altering bending power

  • Laser beam reshapes the cornea
60
Q

What’s the pupillary reaction to increased + decreased illumination?

A

Increased:
- Parasympathetic - pupils constrict to limit light hitting retina

Decreased:
- Sympathetic - pupils dilate to allow as much light as possible to reach the retina

61
Q

What’s Phototransduction?

A

Conversion of light energy to an electrochemical response by the photoreceptors (rods and cones)

  • Phototransduced rods and cones need to activate optic nerve neurons (generate action potential)
62
Q

How do we visualise colour?

A
  • Visual pigment is in the outer segments of photoreceptors
  • Each lamellae is made up of cell membrane - integrated into this cell membrane:

Rods = Rhodopsin = B+W vision

Cones = Iodopsin = Colour vision

Iodopsin and Rhodopsin molecules differ in their spectral sensitivity

Semester II - GHD (20 decks)

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