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Nervous System > Applied Anatomy and Physiology of the Orbit and the Eye > Flashcards

Applied Anatomy and Physiology of the Orbit and the Eye Flashcards

1
Q

The fibrous coat (white, outermost) of the eye has two components - what are they?

A
  • Sclera

- Cornea

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2
Q

Describe the structure and function of the sclera.

A
  • Component of the fibrous coat
  • Opaque posterior 5/6
  • Gives attachment to eye muscles
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3
Q

Describe the structure and function of the cornea.

A
  • Component of the fibrous coat
  • Transparent anterior 1/6
  • A window that allows light to enter eyeball
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4
Q

The vascular coat (orange, middle, contains a rich supply of blood vessels) of the eye has three components - what are they?

A
  • Choroid
  • Ciliary body
  • Iris
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5
Q

Describe the structure and function of the choroid.

A
  • Component of the vascular coat
  • Posterior
  • Supplies blood to outer layers of retina
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6
Q

Describe the structure and function of the ciliary body.

A
  • Component of the vascular coat
  • Middle
  • Suspends the lens
  • Produces aqueous humor
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7
Q

Describe the structure and function of the iris.

A
  • Component of the vascular coat
  • Anterior
  • Hangs from ciliary body
  • Incomplete due to anterior aperture i.e. the pupil
  • Controls the diameter of the pupil and thereby controls the amount of light rays entering eyeball
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8
Q

The fibrous coat (innermost) of the eye has one component - what is it?

A

Retina.

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9
Q

Describe the structure and function of the retina.

A
  • Contains light-sensitive rods and cones
  • Has ten different layers
  • Outer layers supplied by choroid
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10
Q

Describe the structure and function of the lens.

A
  • Transparents, crystalline, biconvex structure
  • Suspended by zonules (suspensory ligaments) from ciliary body
  • Can change shape i.e. become more/less convex, thus control focal distance of the eye
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11
Q

Where are the ciliary body and suspensory ligaments present?

A

360° around the lens.

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12
Q

Describe the structure and function of the anterior segment of the eye.

A
  • In front of the lens
  • Contains aqueous (liquid) humor, which helps to maintain ocular pressure (approx. 21mmHg)

Further divided into;

  • Anterior chamber in front of iris
  • Posterior chamber behind iris
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13
Q

Describe the structure and function of the posterior segment of the eye.

A
  • Behind the lens
  • Filled with vitreous (gel) humor, which helps to cushion the retina (can become liquid in trauma, allowing more chance for retina to detach from choroid)
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14
Q

Describe the movement of aqueous humor through anterior segment of the eye.

A
  • Aqueous humor produced in ciliary body
  • Flows into posterior chamber
  • Flows through pupil to anterior chamber
  • Drains out of eye through the angle of the anterior chamber; trabecular meshwork –> Schlemm’s canal –> episcleral veins
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15
Q

Describe the skin of the eyelid.

A
  • Thin with hair follicles and sebaceous glands

- Margins of eyelid have special hair follicles with their own sebaceous glands (blocked gland results in sty)

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16
Q

Describe the structure and function of the levator palpabrae superioris.

A
  • Starts at apex of orbit
  • Runs just under roof of orbit to front where its tendons attach to conjunctiva, tarsal plate and skin of eyelid
  • Elevates upper eyelid
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17
Q

Describe the structure and function of the orbiculares oculi.

A
  • Runs through eyelid and orbit

- Helps to close eyelid

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18
Q

Describe the structure and function of the tarsal plate of the eyelid.

A
  • Gives eyelid form
  • Meibomian glands are inside it, which produce meibum (oily substance that prevents the evaporation of the eye’s tear film)
19
Q

Describe the structure and function of the conjunctiva.

A
  • Mucus membrane, thin, vascular
  • Secretes fluid
  • Covers inner surface of eyelids and loops back over sclera
  • Does not cover cornea (as it is highly vascularised so leakage over the cornea would affect vision)
20
Q

Describe the structure and function of the lacrimal apparatus.

A

Situated in the orbit laterally.

  • Ducts open into conjunctival sac
  • During each blink, eyelids spread tears evenly on surface of cornea
  • Tears drain through punctae on medial side of each eyelid
  • Drains into lacrimal sac, which sits over lacrimal bone
  • Then drains through nasolacrimal duct into inferior meatus of nasal cavity

When blinking, the sac is pulled open, creating a negative pressure that pulls the tears through the canaliculi and into the sac.

21
Q

Describe the innervation of the lacrimal apparatus.

A

Parasympathetic (secretomotor) fibres from facial nerve (CN VII).

22
Q

Describe the structure and function of the intrinsic muscles of the eye.

A
  • Begin and end inside eyeball- Present in iris or ciliary body
  • Control pupil diameter
  • Help alter lens curvature to enable us to see nearby objects
23
Q

Name the intrinsic muscles of the eye.

A
  • Ciliaris muscle
  • Constrictor pupillae
  • Dilator pupillae
24
Q

Describe the function and innervation of the ciliaris muscle.

A
  • Contracts and changes shape of lens, allowing ability to see nearby objects (accommodation)
  • Innervated by parasympathetic fibres (oculomotor nerve, CN III)
25
Q

Describe the structure, function and innervation of the constrictor pupillae.

A
  • Concentric muscle
  • Constricts pupil
  • Innervated by parasympathetic fibres (oculomotor nerve, CN III)
26
Q

Describe the structure, function and innervation of the dilator pupillae.

A
  • Radial muscle
  • Dilates pupil
  • Innervated by sympathetic plexus around blood vessels
27
Q

Describe the structure and function of the extrinsic muscles of the eye.

A
  • Originate from the orbit and attach to the sclera

- Help to move the eye when contracted

28
Q

Name the extrinsic muscles of the eye.

A

4 straight muscles;

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

2 oblique muscles;

  • Superior oblique
  • Inferior oblique
29
Q

Describe the structure of the superior oblique.

A
  • Starts at apex of orbit
  • Runs close to medial wall
  • Comes anterior, attaches to roof of orbit via trochlea before changing direction to attach to sclera posteriorly
30
Q

Describe the structure of the inferior oblique.

A
  • Starts at front of orbit (all other muscles start at apex)

- Slings under eyeball and attaches laterally and posteriorly to sclera

31
Q

Describe the innervation of the extrinsic muscles of the eye.

A 
Oculomotor nerve (CN III) supplies; 
- Medial rectus
- Inferior rectus
- Lateral rectus
- Inferior oblique
(- LPS)
Trochlear nerve (CN IV) supplies; 
- Superior oblique
Abducens nerve (CN VI) supplies;
- Lateral rectus
32
Q

CNs III, IV, VI all enter the orbit through which opening?

A

Superior orbital fissure.

33
Q

Name the three branches of the ophthalmic division of the trigeminal nerve (CN V).

A
  • Nasociliary
  • Lacrimal
  • Frontal
34
Q

The ophthalmic division of the trigeminal nerve (CN V) enters the orbit through which opening?

A

Superior orbital fissure.

35
Q

The maxillary division of the trigeminal nerve (CN V) enters the orbit through which opening?

A

Inferior orbital fissure.

36
Q

What artery supplies the orbit?

A

Ophthalmic artery (branch of ICA).

37
Q

Which veins drain the orbit?

A

Superior and inferior ophthalmic veins –> cavernous sinus –> IJVs.

38
Q

The internal jugular veins leave the skull through which openings?

A

The jugular foramen.

39
Q

Describe the structure of the cavernous sinuses.

A
  • Sit on either side of body of sphenoid bone

- Situated between two layers of dura mater (lined by squamous endothelium)

40
Q

Embryology: describe the development of the eye from the neural tube.

A
  • Develops as an extension of the brain
  • The brain develops from the neural tube
  • The notochord send signals to the ectodermal cells to enlarge and form a neural plate
  • With further development, the neural plate sinks down and the ends fold up to meet and form the neural tube at the dorsal end of the embryo
41
Q

Embryology: describe the formation of the optic vesicles.

A
  • Optic vesicles grow outwards from diencephalic part of neural tube towards surface ectoderm
  • Once at surface, they send signals for epithelium to thicken, forming the lens placode
  • Lens placode invaginates inwards and pushes the optic vesicle inwards to form an optic cup
  • A stalk connects the optic cup to the neural tube
42
Q

Embryology: describe the formation of the eye’s components from the optic cup.

A
  • A 2 layered optic cup is formed in the retina
  • The mesenchyme sitting around it condense to form the choroid and sclera
  • The lens vesicle loses its connection with the surface ectoderm and forms the crystalline lens
  • The anterior epithelium form the cornea
  • The 10th layer of the retina forms from the outer layer of the optic cup while the other 9 form from the inner layer (potential space between these layers, important clinically as they can separate)
43
Q

Embryology: describe the formation of the choroid fissure.

A

As the optic cup is forming, blood vessels create a groove in the developing retina and optic nerve which is called the choroid fissure. This fissure eventually becomes closed off but the artery remains and goes on to become the central retinal artery, which supplies the surface of the retina.

Nervous System (45 decks)

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