Intro to Eye Flashcards
Where do tears flow from?
Lacrimal sac
Nasolacrimal duct
What does the conjunctiva NOT cover?
The cornea
What gives shape to the eyelids?
Tarsal plate
What is found inside the tarsal plate?
The Meibomian gland
In embryology, where do optic vesicles grow outward from>
From diencephalic part of neural tube towards surface ectoderm
What are the layers of the eyeball?
Fibrous coat
Vascular coat
Sensory coat
What is found in the fibrous coat?
Lens
What is found in the vascular coat?
Aqueous humor
What is found in the sensory coat?
Vitreous humor
What is the pupil?
The space between the ciliary body and the iris
How is the lens suspended?
From the ciliary body by suspensory ligaments
What makes up the outer layer of the eye?
Cornea
Sclera
Is the cornea transparent?
Yes
Is the sclera transparent?
No
What is the ciliary body involved in?
The production of aqueous humor
What are the two chambers of the eye?
Anterior chamber
Posterior chamber
What chamber is aqueous humor produced in?
Posterior chamber
What is the trabecular meshwork?
Draining system
Where is the trabecular meshwork found?
Outside the Schlemm’s canal
What is the choroid made up of?
Fenestrated blood vessels of varying diameter
What does the choroid do?
Supplies the retina with blood
How many layers does the retina have?
10
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)
- Epithelium
- Bowmans membrane
- stroma
- Descements layer
- 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
- Mucinous layer (30%)
- Aqueous layer (69%)
- 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)
