The eye and visual system 17.02.23 Flashcards
what is a corneal reflex?
Eye can sense something on its surface so we blink
what are the 3 layers of the eye?
- Outer layer (sclera and cornea)
- Middle layer (Uvea)
- Inner layer (retina)
What is the structure of the sclera?
tough fibrous outer coat, made up of collagen in a pattern
What is the function of the sclera?
- Transparent for light transmission
- Tough because it is a barrier to trauma and infection
- it is responsible for 2/3 of the refractive power of the eye
What is the function of the cornea?
- Transmission of light
- Refraction
What is the structure of the cornea?
- Transparent (opaque indicated cataracts)
- Smooth spherical surface
- Corneal clarity is maintained by pumping water out
- Surface epithelium can be repaired
What are the 5 layers of the cornea?
Epithelium (can regenerate)
Bowman’s Layer
Stroma
Descemet’s layer
Endothelium (can’t regenerate)
What three structures make up the middle layer of the eye?
- Iris (extension of the choroid)
- Ciliary body (specialised layer of muscle cells)
- Choroid
What is the function of the choroid?
It is the blood supply to the outer third of the retina and provide oxygen and nourishment to the outer retina
- Highly pigmented
What is the function of the iris?
- The coloured part of the eye
- Contains dilator (make pupil larger: sympathetic)
- and sphincter pupillae muscles (makes pupils smaller: parasympathetic)
- and controls pupillary reflexes
what is the function of the ciliary body?
- It has a specialised epithelial lining of glandular epithelium
- This produces aqueous humour
- The ciliary (smooth) muscle controls accommodation (focusing)
- Maintains pressure in eye
What is the function of the retina?
- Contains specialised cells: photoreceptors
- Organ of photo transduction
- Produces vitreous humour (helps maintain pressure)
What is the macula lutea?
this is responsible for detailed central vision of the retina and it contains the fovea centralis which is the centre of the macula.
- If this gets damaged, vision is severely impaired
What do cones and rods do?
Cones: see colour and high resolution
Rods: Black and white and low resolution
What cells support the activation of the photo receptor cell?
When light enters the eye it stimulates the photoreceptor cells with the help of:
- Bipolar cells
- Amacrine and horizontal cells
- Muller glial cells
Then the retinal ganglion cells of a neuron receive this information from the photoreceptors
What humour is in the anterior segment?
Aqueous humour
- Which is the nutrition to the lens and cornea
- And maintains intraocular pressure
What is the function of the lens?
- Biconvex
- responsible for 1/3 refractive power of the eye
- accomodation
What is emmetropia?
6/6 vision
What is Hypertropia?
- Underpowered to focus near objects on retina
- far sighted
- Will receive a + lens
What is Myopia?
- Overpowered so can’t focus far objects on retina
- Near sighted
- Will receive a - lens
What humour is in the posterior segment?
- Vitreous humour
- This is a avascular viscoestalic gel
- Contains Hyaluronic acid and collagen
What adnexae help support the eye?
- Eyelids
- Conjunctiva
- tear film
what are the three layers of the tear film?
- Anterior: Lipid
- Middle: aqueous
- Posterior: Mucous
What is the function of the lipid layers of the tear film and how is it made?
function: Prevents evaporation
Made by: Meibomian gland and Zeis
What is the function of the aqueous layers of the tear film and how is it made?
Function is for fluidity and nutrition and prevents infection
Made by the lacrimal and accessory lacrimal glands
What is the function of the mucosal layers of the tear film and how is it made?
Lubricates and aids even distribution of tears
Made by the conjunctival goblet cells
What is the arterial supply to the inner retina?
Internal carotid artery:
- into the ophthalmic artery, central retinal artery and ciliary arteries
External Carotid artery:
- Facial artery supplies the medial lid and orbit
How is the eye drained (which veins)?
- drained by branch retinal veins
- central retinal v.
- ophthalmic v.
- cavernous sinus
- Internal jugular v.
What is the blood supply to the outer retina?
Outer 1/3 by the choroid
- posterior ciliary artery
How is the choroid drained?
By vortex veins, usually one for each quadrant
What parts of the eye have lymphatics drainage?
Conjunctiva and lids do have lymphatic drainage to submandibular nodes
What is the structure of the cornea?
- Transparent (opaque indicated cataracts)
- Smooth spherical surface
- Corneal clarity is maintained by pumping water out
- Surface epithelium can be repaired
