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Nervous System > Eyeball Anatomy > Flashcards

Eyeball Anatomy Flashcards

1
Q

What are the three layers of the eyeball?

A
  1. Outer fibrous coat (sclera and cornea)
  2. Middle vascular coat
  3. Inner sensory layer (retina)
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2
Q

What are the parts of the middle vascular coat?

A
  • Three parts: choroid (posterior), ciliary body (anterior) and the iris hangs from the iris
  • It is an incomplete layer as the it leaves opening for pupil
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3
Q

What are the parts of the inner sensory layer?

A
  • Contains light sensitive rods and cones
  • Where image of an object is formed
  • Incomplete layer – it ends just in front of the equator line* in a very serated margin called the ora serata

*imaginary line

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4
Q

What is the sclera?

A

The opaque posterior 5/6 which gives attachments to muscles move eye when they contract (the white of the eye)

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5
Q

What is cornea?

A

Projects from the anterior part of the sclera. It is the anterior 1/6 which is transparent to allow light rays to enter

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6
Q

What is the cornea made up of?

A

Made up of collagen, but the collagen fibres are arranged regularly making the cornea transparent and it is through this that light enters the eyeball.

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7
Q

What is the function of the choroid?

A

Blood supply to the outer layers of the retina

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8
Q

What is the function of the iris?

A
  • Controls the diameter of the pupil and thereby control the amount of light rays entering the eyeball
  • Contains concentric and radial muscles which help control diameter of pupil
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9
Q

What is the function of the ciliary body?

A
  • Suspends the lens from zonules (fibrous strands that connect them) and contains muscles that change the shape of the lens (accommodation)
  • Produces aqueous Humor which is fluid which sits in front of the lens.
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10
Q

What is the retina made up of?

A
  • Has light sensitive rods and cones for sight
  • Histologically has ten layers and the outer of these including the layers including roads and cones, receives blood from the choroid which it sits on top of.
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11
Q

What structure produces aqueous humor?

A

Ciliary body

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12
Q

What is aqueous humor?

A

Watery fluid secreted by the ciliary body anterior to the lens which helps maintain intraocular pressure

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13
Q

What is the pressure of aqueous humor and how is it maintained?

A

21mmHg and is constanty being produced, circulated and reabsorbed

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14
Q

What is the function of vitreous humor?

A

Tamponades the retina by pushing retina back; in cases where the gel becomes liquefied (i.e. after trauma), there is a higher chance of the retina separating from the choroid as the gel is no longer there to tamponade the retina

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15
Q

What are the two segments of the eye?

A

Anterior (in front of lens) and posterior

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16
Q

How is the anterior segment of the eye further divided?

A

Into two more chambers:
• Anterior chamber - in front of iris
• Posterior chamber - behind iris but infront of lens

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17
Q

Describe the pathway of aqueous humor into the anterior segment of the eye

A

Formed by the ciliary body and then flows into the posterior chamber of the eye, through the pupil and into the anterior chamber of the eye

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18
Q

How is aqueous humor drained?

A

Angle in the anterior chamber -> into the trabecular meshwork -> schlemms canal -> episcleral veins (veins just above sclera)

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19
Q

What are the three openings at the apex of the orbit (at the back)?

A

Optic foramen
Superior orbital fissure
Inferior orbital fissure

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20
Q

What bone make up the orbit?

A

Frontal bone, zygomatic bone, maxillary bone, sphenoid bone, lacrimal bone, ethmoid bone (medial wall of orbit) (and small part of the palatine bone).

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21
Q

Why are the walls of the orbit weak and what is the clinical significance of this?

A

Due to the presence of the grooves but also because of their relationship with the paranasal air sinuses:

Thin bone between orbit and paranasal sinuses (frontal and maxillary) make the area susceptible to injury

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22
Q

Why is the orbit much longer than the eyeball?

A

Filled by fat which is important for providing support for the eyeball

And is the last fat that is lost when going on starvation diet

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23
Q

What is the length of the eyeball in comparison to the length of the orbit?

A

Eyeball is 24mm and the orbit is 40mm

24
Q

What occurs in thyroid eye disease?

A

Hypertrophy or increase in the fat content in the orbit -> exophthalmos

25
Q

Describe the structures found int the eyelid

A
  • Specialised hair follicle and sebaceous gland for eyelashes at base
  • Conjunctiva - muscous membrane on inside
  • Lavetor palpebrae superioris
  • Orbicularis oculi
  • Tarsal plate
  • Meibomian glands (in tarsal plate)
  • Oily secretory glands for tear film
26
Q

Describe the pathway and function of Lavetor Palpebrae Superioris

A

Apex of orbit running under the roof until it’s tendons attach the conjunctiva and the tarsal plate and skin of eyelid  elevates the upper eyelid

27
Q

What two muscles are found in the eyelids?

A

Lavetor palpebrae superioris and oculars oculi

28
Q

What is the conjunctiva?

A

Thin vascular membrane covering surface of eyelids and sclera (but not cornea); it runs over the back of the eyelids and turns at the superior fornix to cover the sclera

29
Q

Why is conjunctive not found over the cornea?

A

Because the conjunctiva is a very vascular membrane where the blood vessels and capillaries often leak, so you do not want the vasculature to cover transparent membrane (cornea) and obstructing the amount of light that enters

30
Q

Where is the lacrimal gland situated?

A

In the roof of the orbit (quite anteriorly)

31
Q

What nerve innervates the lacrimal gland?

A

Secretomotor from the facial nerve

32
Q

What the the effect of stimulation of the lacrimal gland by the facial nerve?

A

Tears drain through puntae (upper and lower eyelid) on the medial side into the lacrimal sac which then drain through the nasolacrimal due into the inferior meatus of the nasal cavity.

33
Q

How are tears drained throughout the punctae?

A

Blinking (contraction of orbiculares oculi) pulls the lacrimal sac open which creates a negative pressure, sucking the tears through the puncture and canalicli and into the sac.

34
Q

What are the intrinsic muscle of the eye?

A

Begin ad end inside the eyeball -> control pupil diameter and alter lens curvatures for accommodation

35
Q

What are the extrinsic muscles of the eye?

A

Originate in the orbit and attach to sclera of eyeball -> move the eye

36
Q

Name three intrinsic eye muscle and their innervation

A
  • Ciliaris muscle and constrictor pupillae by parasympathetic (CN III)
  • Dilator pupillae by sympathetic (plexus around blood vessels)
37
Q

What is the function of the ciliaris muscle?

A

Contraction changes the shape of the lens for accommodation

38
Q

What are the attachments of the superior oblique muscle?

A

Originates at the apex of the orbit, runs close to the medial wall and attaches to the trochlear, where it changes direction and attaches to the sclera posteriorly

39
Q

What are the attachments of the inferior oblique muscle?

A

Originates at the front of the orbit (only muscle) and slings the under surface of the eyeball to go obliquely and attach laterally and posteriorly to the sclera

40
Q

Which nerve provides general sensory innervation to the eye?

A

Ophthalmic and maxillary division of the trigeminal nerve

41
Q

What three branches does the ophthalmic division of the trigeminal give off after it enters via the superior orbital fissure?

A
  • Nasociliary nerve
  • Lacrimal branch
  • Frontal branch
42
Q

What is the pathway of the maxillary division of the trigeminal nerve?

A

Nerve passes through the inferior orbital canal in the floor of the orbit, and exits through the infraorbital foramen as the infraorbital nerve.

43
Q

What branch of the ICA provides blood supply to the orbit?

A

Ophthalmic artery

44
Q

Where does the ophthalmic artery enter the orbit and what does it supply?

A

Via the optic foramen and supplies all structures in the obit (i.e. lacrimal gland, muscles), and also some branches to the medial nasal cavity and forehead.

45
Q

Name three groups of branches that come from the ophthalmic artery once inside the orbit

A
  1. Central retinal artery
  2. Short posterior ciliary arteries
  3. Long posterior ciliary arteries
46
Q

What does the central retinal artery go on to supply?

A

Goes to the centre of the eyeball and supplies inner layers of the retina (choroid supplies blood to outer layers)

47
Q

What artery supplies inner layers of the retina?

A

central retinal artery

48
Q

What do the short posterior ciliary arteries supply?

A

Posterior choroid (and outer retina)

49
Q

What do the long posterior ciliary arteries supply?

A

Anterior choroid, ciliary body and iris

50
Q

What is the optic disc?

A

Filled with emerging nerve fibres that travels posteriorly

51
Q

Why is the optic disc the physiological blind spot?

A

Does not have any rodes and cones

52
Q

What are the four quadrants that the funds is divided into for an ophthalmoscopy?

A

Upper and lower nasal quadrants and upper and lower temporal quadrants.

53
Q

Describe the venous drainage of the orbit

A

Through superior and inferior ophthalmic veins which drain into the cavernous sinus usually though the superior orbital fissure

54
Q

What epithelium type are the venous sinuses lined with?

A

Squamous epithelium called the endothelium

55
Q

Where is the cavernous sinus located?

A

On either side on the sphenoid bone

56
Q

What other structures travel through the cavernous sinus?

A

ICA, CN II, III, IV, V and VI

Nervous System (47 decks)

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