Intro to Eye Flashcards by Annie Caldwell

Where do tears flow from?

Lacrimal sac

Nasolacrimal duct

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What does the conjunctiva NOT cover?

The cornea

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What gives shape to the eyelids?

Tarsal plate

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What is found inside the tarsal plate?

The Meibomian gland

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In embryology, where do optic vesicles grow outward from>

From diencephalic part of neural tube towards surface ectoderm

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What are the layers of the eyeball?

Fibrous coat
Vascular coat
Sensory coat

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What is found in the fibrous coat?

Lens

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What is found in the vascular coat?

Aqueous humor

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What is found in the sensory coat?

Vitreous humor

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What is the pupil?

The space between the ciliary body and the iris

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How is the lens suspended?

From the ciliary body by suspensory ligaments

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What makes up the outer layer of the eye?

Cornea

Sclera

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Is the cornea transparent?

Yes

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Is the sclera transparent?

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What is the ciliary body involved in?

The production of aqueous humor

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What are the two chambers of the eye?

Anterior chamber

Posterior chamber

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What chamber is aqueous humor produced in?

Posterior chamber

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What is the trabecular meshwork?

Draining system

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Where is the trabecular meshwork found?

Outside the Schlemm’s canal

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What is the choroid made up of?

Fenestrated blood vessels of varying diameter

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What does the choroid do?

Supplies the retina with blood

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How many layers does the retina have?

What are the important layers of the retina to remember?

pigment epithelial layer
layer of rods and cones
nerve fibre layer

What is the inner layer of the retina supplied by?

Central retinal artery

branch of ophthalmic artery
branch of ICA

What is the fovea centralis?

Part of the retina which has the highest visual acuity

Why does the fovea centralis have the highest visual acuity?

It is packed with cones

What is the lens?

Transparent, crystalline biconvex structure which is suspended by zonules from the ciliary body .

Can the lens change shape?

Yes

What feature of the lens makes it transparent?

Avascularity

What is lens opacification called?

Cataracts

What does the basal membrane on the outside of the lens form?

Lens capsule

Layers of cornea (histology)

1. Epithelium 2. Bowmans membrane 3. stroma 4. Descements layer 5. Endothelium

What epithelium is found in cornea?

Stratified squamous non keritanised

What is bowmans membrane?

Basement membrane of corneal epithelium

What is the stroma of the cornea made up of?

Connective tissue

What allows light rays to pass through the stroma of the cornea?

Collagen uniformly spaced and arranged very regularly | Avascularity

How does the stroma of the cornea get nutrition?

Tear duct on the top Aqueous on the bottom Sclera around it

What is Descemet's layer?

Basement membrane of corneal endothelium

Histology of endothelium of cornea

Single layer normally 2500 cells/mm2

Why does avascularity confer an advantage during corneal graft surgery?

Lesser chance of foreign antigens from the corneal graft being recognised by the recipient, so lesser chance of graft rejection

What is a name given to the cornea due to its avascularity?

Immune privileged site

Functions of tear film

Keeps cornea moist and prevents drying Washes away any particulate foreign bodies Has antibodies and lysozymes to kill microbes Smooths outer surface of cornea providing smooth surface for retraction

How can you see the tear film?

A dye called fluorescein

Layers of tear film

1. Mucinous layer (30%) 2. Aqueous layer (69%) 3. Oily layer (<1%)

Features of the mucinous layer of the tear film

Overlies corneal epithelium

Features of the aqueous layer of the tear film

Overlies the mucinous layer

What is the aqueous layer of the tear film secreted by?

Lacrimal glands

What is the mucinous layer of the tear film secreted by?

Conjuctiva

Features of the oily layer of the tear film

Most superficial

What secretes the oily layer of the tear film?

Meibomian gland

Function of the oily layer of the tear film

Prevents the aqueous layer from being evaporated too quickly

Physiology of the tear film dynamics

Parasympathetic (VII n) secretion of tears into conjunctival sac During a blink, the sharp lower border of the upper eyelid distributes the tear film evenly When the eyelids are open, the aqeous component of the tears begin to evaporate, and the oily layer comes close to the mucin layer When these two layers touch, the tear film breaks up and stimulates further blinking

How is the transparency of the cornea maintained?

Histologically - regular arrangement of collagen in stroma No blood vessels Endothelium cell layer has a pump that actively keeps the aqueous humour out

How does the aqueous humor pump work?

Pump pushes the aqueous humor out The pump constantly maintains a pressure and constant circulation This pressure is trying to push into the cornea (which if successful would ruin the transparency)