Applied Anatomy and Physiology of the Orbit and Eye Flashcards
What are the 3 layers of the eye?
Fibrous coat
Vascular coat
Sensory coat
What makes up the fibrous coat?
Sclera
Cornea
What makes up the vascular coat?
Choroid
Ciliary body
Iris
What makes up the sensory coat?
Retina
What are the 5 layers of the cornea?
- epithelium
- bowmans membrane
- stroma
- descemets layers
- endothelium
What is the epithelium of the cornea?
it is stratified squamous non-keratinised
Cells are quite flat so stratified squamous
Unlike skin it is non-keratinized
What is bowmans membrane?
the basement membrane of the coreneal epithelium
epithelium are always sitting on a basement membrane
What is the stroma?
it is regular arranged collagen and has no blood vessels meaning it is transpartent which is opposite to the sclera
collagen in the cornea are arranged parallel to each other and very uniform meaning light can pass through into the eye
what is descemets layer?
basement membrane for the inner epithelium called the endothelium
What is the endothelium
the inner epithelium which is against the aqueous humor
it is single layered unlike the outer epithelium
Can you see the cornea?
not really as it is transparent
How is the transparency of the cornea maintained?
1 . histologically - regular arrangement of collagen in stroma
- no blood vessels
- endothelium cell layer has a pump that actively keeps the aqueous humor out
What is aqueous humor responsible for?
maintenance of pressure of the eyeball
What may start ot happen if there is not enough endothelium cells?
aqueous humor may start to get into the cornea and it will begin to become hazy
Does avascularity play are role in corneal transplant?
yes
What is the important role of avascularity of the cornea in corneal transplant?
it is a benefit to surgeons
there is a lesser chance of forgein antigens from the corneal graft being recognised by the recipient, so lesser chance of a graft rejection
What are the 2 functions of the ciliary body?
- Has muscles in which help suspend the lens and helps in changing shape of lens
- Production of aqueous humor
Where is aqueous humor drained?
angle of the anterior chamber
Once aqueous humor is at the angle of the anterior chamber, where does the aqueous humor drain?
goes through a trabecular meshwork which acts as a siv
drains into a tube called schlemms canal and then eventually to veins
How many layers make up the retina?
10
What supplies blood to the retina?
the outer layers are supplied by the choroid
the choroid has many blood vessels of different sizes which supply the outer layers of the retina with blood through diffusion
the inner layers of the retina get blood from branches of the central retinal artery
What is A?
pigment epithelial layer
What is B?
layer of rods and cones
What is C?
nerve fibre layer
What is the pigment epithelial layer?
maintains health of retinal rods and cones
(nourishes retinal visual cells)
Age related macular degeneration – dystrophy effecting pigment epithelial layer which leads to destruction of rods and cones
What is the layer of rods and cones?
photosensitive cells
they are photoreceptors responsible for sight
What is the nerve fibre layer?
recieves information as an action potential and takes it to the brain
joins up to form the optic nerve
What is the fovea centralis?
area packed with cones so maximum visual acuity
in the middle of the eye
cones are a lot more sensitive to light changes than rods
in the fovea centralis all the other layers are pushed to the side
Describe the strucutre of the lens
Transparent
crystalline biconvex structure
suspended by zonules from the ciliary body
can change shape (i.e. become less or more convex)
How is the lens transparent and what can this lead to in later life?
For it to be transparent, it needs to be avascular
This avascularity is one of the factors that predisposes it to become opaque later in life
What is cataract?
lens opacification
What are the areas infront and behind the lens called?
infront - anterior segment
behind - posterior segment
WHat is the mucous membrane that lines the inside of the eyelids and the sclera on the front of the eye?
conjunctiva
What muscles contorl the eye lids?
Orbicularis oculi helps close eye
levator pupillae superioris elevates the eyelid
What helps keep the shape and supports the eyelids?
tarsal plate
What do meibomian glands do?
Exocrine glands found along the rims of the eyelid inside the tarsal plate
They produce meibum, an oily substance that prevents evaporation of the eye’s tear film
Where do tears drain?
into the lacrimal sac that drains into the inferior meatus in the nose
What produces tears?
Lacrimal gland is lateral and above to the eye around the LPS, secretes tears onto the surface of the gland
Facial nerve is responsible for secreting parasympathetic of the lacrimal gland
What are the functions of tear film?
- Keeps cornea moist, prevents drying
- Washes away any particulate foreign bodies
- Has antibodies and lysozymes to kill microbes
- Smooths outer surface of cornea providing smooth surface for refraction
What is the strutuce of tear film?
Layer 1: mucinous layer (~30%) overlying corneal epithelium
Layer 2: aqueous layer (~69%) lies over the mucinous layer
Layer 3: oily layer (<1%) is the most superficial
What is the process of tear film breaking up?
During a blink, the sharp lower border of the upper eyelid distributes the tear film evenly
When eyelids are open, aqueous component of tears begin to evaporate, and oily layer comes close to the mucin layer
When these 2 layers touch each other, the tear film breaks up and stimulates further blinking
