Orbit and Eyes Flashcards by Srishti D

How can you get a blowout fracture to the orbit?

Blunt trauma to orbit

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How is a broken bone in the orbit a protective measure?

Contents of orbit sink down into broken bone and are thus protected

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What forms the supraorbital margin?

Frontal bone

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What is the significance of the supraorbital notch?

Neurovascular structures pass through it

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What forms the infraorbital margin?

Zgomatic bone laterally

Maxilla medially

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Which bones break in a blowout fracture?

Thinnest and weakest bones

Lacrimal
More commonly, ethmoid in papyrus region
Or junction between 2

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Which bones make up the roof of the orbit?

Frontal

Lesser wing of sphenoid

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Which bones make up the floor of the orbit?

Maxilla - orbital plate of
Zygomatic
Palatine

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Which bones make up the lateral wall of the orbit?

Zygomatic

Greater wing of sphenoid

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Which bones make up the medial wall of the orbit?

Maxilla
Lacrimal
Ethmoid
Body of sphenoid

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What colour is the sclera?

White

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How much of the surface of the eyeball is the sclera?

5/6

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What are the functions of the sclera?

Maintains shape of globe
Offers resistance to internal and external forces
Provides attachments for extraocular muscles

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What is the sclera made of?

Collagen

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What is the pattern of collagen in the sclera?

Laid down in whorls

Makes it very tough

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How much of the surface of the eyeball is the cornea?

Anterior 1/6

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Are the cornea and sclera continuous?

Yes

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What is the principal refracting component of the eye?

Cornea

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How much light does the cornea bend?

60%

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What makes the cornea optimum for vision

Avascular
Transparent
Structure of collagen
Not many cell bodies

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What are the five histological layers of the cornea, from outside to inside?

Epithelium
Bowman's layer
Stroma
Descemet's membrane
Endothelium

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What kind of layer is the epithelium?

Mucous membrane

Multiple cells

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How many layers is the endothelium of the cornea?

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Which part of the cornea is continuous with the sclera?

Stroma

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How is collagen organised in the cornea?

Uniform in diameter Evenly spaced Run parallel to each other in bundles = lamellae Adjacent lamellae at angles to each other

What does scleral opacity vary depending on?

Composition of stroma Hydration Size and distribution of collagen

How does the collagen of the cornea often heal?

Doesn't grow back in ordered way Scar formation Loss of transparency

What is the anterior chamber?

Area just behind cornea

What is the anterior chamber angle?

Junction between iris and cornea

What are the key structures in the anterior chamber angle?

Cornea Trabecular meshwork Canal of Schlemm Ciliary body

What is the trabecular meshwork?

Holes through which aqueous humour drains

What can happen if the trabecular meshwork is clogged?

Pressure in eye increases

What is the route of aqueous flow through the anterior chamber angle?

Past ciliary body Through trabecular meshwork Through canal of Schlemm

What are the three layers of the eye and what are their functions?

1. Cornea and sclera > strength 2. Uvea > nutrition 3. Retina > sight

What are the functions of the ciliary body?

Formation of aqueous humour Tethers lens Accommodation

What forms the aqueous humour?

Ciliary epithelium

What tethers the lens?

Ciliary processes

What is responsible for accommodation?

Ciliary muscle

Where are the ciliary processes located?

Anteriorly only

What is aqueous humour important for?

Maintaining health of lens and cornea | Creates intraocular pressure

How many cell layers is the ciliary epithelium?

Where is the ciliary epithelium?

On ciliary processes

What does aqueous humour drain into?

Venous supply

What structures does accommodation involve?

Lens Ciliary muscle Zonules attached to lens

What are zonules?

Ligaments between ciliary processes and lens | Pull lens to change its shape

Describe the ciliary muscle

Within ciliary body Innervated by parasympathetic nervous system carried by CN III Smooth muscle - like sphincter

What does the ciliary muscle do to allow you to see things far away?

Relax > aperture of sphincter open > zonules stretch > lens becomes skinny

What does the ciliary muscle do to allow you to see things close by?

Contract > aperture of sphincter smaller > zonules relax > lens becomes fat

What is presbyopia?

Loss of accommodation with age

Why does presbyopia happen?

Reduction in flexibility of lens and zonules

What are the structures that make up the uvea?

Ciliary body | Iris

What is the function of the iris?

Controls size of pupil > controls light entry

Which muscles make up the iris?

Sphincter pupillae | Dilator pupillae

What does the sphincter pupillae do?

Constrict pupil

What is the sphincter pupillae innervated by?

Parasympathetic fibres of CN III

What does the dilator pupillae do?

Dilate pupil

What is the dilator pupillae innervated by?

Sympathetic nervous system

Is the dilator pupillae a real muscle?

No, it's specialised myoepithelium

What is the choroid?

3 layers of blood vessels

What is the most important layer of the choroid and where is it?

Choriocapillaris | Just below retina

Where is the choroid?

Underneath retina

What does the choroid supply?

Retina

What are the parts of the retina?

Optic nerve head/optic disc Fovea/foveola - in middle Macula - around fovea, defined by pigment Posterior pole - around macula Ora serrata - retina joins rest of inside of eyeball

What are the fovea and macula important for?

Central vision

Describe the fovea?

High visual acuity Avascular - gets nutrients from choroid High density of cones No rods

What forms the optic nerve?

Axons of ganglion cells as they exit retina to pass visual information to higher cortical areas

What is the lamina cribrosa?

1/3 of scleral collagen crosses optic nerve Dense - 3-10 sheets Sieve-hole transmitting nerve fibres Provides some structure to optic nerve

What happens to the lamina cribrosa when intraocular pressure increases?

Holes stretched Press on axons of ganglion cells Causes damage

What are the four main arteries of the eye?

``` Central retinal artery Ciliary arteries - Long posterior ciliary artery - Short posterior ciliary artery - Anterior ciliary artery ```

Where is the central retinal artery from?

Internal carotid > ophthalmic > 1st branch

What is the course of the central retinal artery?

Branches off ophthalmic nerve Pierces optic nerve Travels in optic nerve Fans out on surface of retina

What does the central retinal artery supply?

Inner retina

What artery are the posterior ciliary arteries branches of?

Ophthalmic artery

What is the course of the posterior ciliary arteries?

Branch off ophthalmic artery Enter back of eye around optic nerve Depending on how far they travel called short/long

How many branchlets of posterior ciliary arteries are there?

7-11

What do the long posterior ciliary arteries supply?

Travel in choroid all the way forward - Ciliary body - Iris - Some regions of retina via choroid

What do the short posterior ciliary arteries supply?

Choroid around optic nerve

What is the course of the anterior ciliary artery?

Ophthalmic artery > muscular artery > anterior ciliary artery Travels on outside of globe towards front

What does the anterior ciliary artery supply?

Anterior structures of eye - Conjunctiva - Some of sclera - Forms ring around cornea

What supplies the outer retina - and the photoreceptors within it?

Posterior ciliary artery

What structures make up the eyelid?

``` Skin - Glands - Eyelashes Muscles - Orbicularis oculi - Levator palpebrae superioris Lacrimal apparatus - Lacrimal gland and ducts - Nasolacrimal sac and duct ```

What is the function of orbicularis oculi?

Close eyelid

Which nerve innervates orbicularis oculi?

CN VII

What is the function of levator palpebrae superioris?

In upper eyelid only | Opens eyelid

Which nerve innervates levator palpebrae superioris?

CN III