Introduction to Nervous System and Anatomy of the Eye Flashcards
What are the 3 layers of the eye from outside in?
- Fibrous coat
- Vascular coat
- Sensory coat
What are the 2 components of the fibrous coat?
- Cornea
- Sclera
What are the 3 components of the vascular coat?
- Ciliary body
- Iris
- Choroid
What part of the eye is considered the sensory coat?
Retina
What part of the eye is transparent?
Cornea
What are the 2 types of humor found in the eye?
- Aqueous humor
- Vitreous humor
What are the 5 layers of the cornea?
- Epithelium
- Bowman’s membrane
- Stroma
- Descemet’s layer
- Endothelium
What type of epithelium is found in the cornea?
Stratified squamous non-keratinised epithelium
What is Bowman’s membrane?
Basement membrane of corneal epithelium
What is the stroma?
Regularly arranged collagen that has no blood vessels
How thick is the endothelium of the cornea?
Single layer
How is the transparency of the cornea maintained?
- Histologically by the regular arrangement of collagen in stroma
- No blood vessels
- Endothelium cell layer has a pump that actively keeps the aqueous humor out
Why is the avascularity of the cornea a benefit to surgeons when performing corneal transplants?
It means there is a lesser chance of foreign antigens from a corneal graft being recognised by the recipient so lesser chance of a graft rejection
What does the avascularity of the cornea lead researchers to believe?
It is an immune privileged site
What produces aqueous humor?
Ciliary body
Where is the aqueous humor found in the eye?
Anterior segment
Where is the vitreous humor found in the eye?
Posterior segment
How is the eye divided into segments?
- Anterior segment in front of the lens
- Posterior segment behind the lens
How is the anterior segment of the eye divided into chambers?
- Anterior chamber is in front of the ciliary body
- Posterior chamber is behind the ciliary body
What are the 3 important layer of the retina and choroid to remember?
- Pigment epithelial layer
- Layer of rods and cones
- Nerve fibre layer
What is the choroid made from?
Fenstrated blood vessels of varying diameter
What do the blood vessels of the choroid supply?
The outer layers of the retina with blood by diffusion
Where do the inner layers of the retina get blood from?
Branches of the central retinal artery
How does the fovea centralis achieve ,maximum visual acuity?
Packed with cones
What is the lens?
Transparent, crystalline biconvex structure which is suspended by zonules from the ciliary body. It can change shape.
What is one of the factors that can predispose the lens to becoming opaque in later life?
For it to be transparent it needs to be avascular therefore avascularity is one of the predisposing factors
What is lens opacification known as?
Cataract
What are the 4 functions of the 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
How can you clinically see the tear film?
After staining with a dye called fluorescein
What are the 3 layers of the tear film?
- Mucinous layer (~30%) overlying corneal epithelium
- Aqueous layer (~69%) over the mucinous layer
- Oily layer (<1%) is the most superficial
What is responsible for the innervation of the secretion of tears into the conjunctival sac?
Parasympathetic (VII)
How long from blinking does it take for the tear film to break up?
4 seconds
How long after blinking does it take for ocular discomfort to occur?
5 seconds
How is the tear film distributed evenly?
During a blink, the sharp lower border of the upper eyelid distributes the tear film evenly
What happens to the tear film when the eyes are open?
Aqueous component of tears begin to evaporate and oily layer comes close to the mucin layer
What happens when the mucin layer touches the oily layer of the tear film?
The tear film breaks up which stimulated further blinking
How does the eye develop?
Optic vesicles grow outwards from diencephalic part of the neural tube towards surface ectoderm
