Eye anatomy and vision Flashcards
Identify three layers of the eye and how the eye is divided up
- 3 layers: outer fibrous tunic (maintains shape), middle vascular tunic (blood supply), inner neural layer (nerve cells that convert light into action potentials)
- Interior of the globe divided into anterior and posterior segments
a) anterior (front) = everything infront of iris. Further divided into anterior chamber = infront of iris, posterior chamber = between lense and iris
b) posterior = behind lense - internal fluid support by aqueous (anterior) and viterous (posterior) humours
Purpose of the eye
- organ of sight
2. turn incoming light into action potentials
What does the optic nerve do
- Take action potentials to the visual cortex of the brain (occipital lobe)
Which cranial nerve is the optic?
SECOND
Where does the eye develop from and were deos it “sit”
- develops from the optic cup of the embryonic diencephalon
2. sits in the bony orbit of the skull which varies between species
Where does light have to pass through
- Cornea at very front
- through anterior segment
- pupil (hole in iris)
- lense
- viterous humour (jelly like)
What are the functions of the first adnexa of the eye?
- eyelid
- protect eye
- Produce the lipid component of the tear film
- spread and move tears over eye surface
- remove foreign material
- close to exclude light
What is the space between the eyelids called, corners of eye called, movement controlled
- Palperbral Fissue
- corners = canthi = medial and lateral ligaments which hold the lids at these points
- movement controlled by cranial nerve 7, facial nerve
What is the conjunctiva and what is its role
- the mucous membrane that is inside eyelids (pink stuff)
- covers everything, highly vascular, lot of lymphoid tissue, lot of gobles cells produce mucin
- folds back on itself (formix)
What are the different names for the conjunctiva?
- palperbral conjunctiva - on eyelid
- Bulbar conjunctiva - onto eyeball
- Nicititating conjunctiva - covers thirs eyeball
3rd eyelid
- nicitating membrane
- sits in ventral medial aspect of orbit
closes when eyeball retracts passively - supported by cartilage
- lacromal (tear) gland at base produces some aqueous component of tear film
What are the three components of tears and why
three components
- lipid = eyelids tarsal gland
- mucin = goblet cells of conjuctiva
- aqueous 1/3 from gland at base of 3rd eyelid, 2/3 from lacrimal gland in dorsal lateral part of orbit
Structures of the outer fibrous tunic
- made up of 2 things
- Sclera = white = covrs whole eyeball except for cornea
- Cornea = transparent at front of eye = transmit and refract light
Avascular
What are the layers of the cornea
- Anterior epithelium - squamous outermost and columnar inner. Many pain receptors
- Stroma = collagen fibrils which form lamellae. If cloudy = disruption to lamellae arrangement
- descement’s membrane lies causal to stroma, produced by endothelium
- ENdothelium = innermost. Produced Descement’s membrane and actively pumps water out of cornea = maintains clarity of stroma
Structures of vascular tunic
- sits beterrn fibrous tunic and neural layer.
- termed uvea
- Anterior uvea = iris and ciliary body
- Posterior uvea = choroid
Iris
- sphincter with a constrictor (around pupil) and dilator muscle
- arises from cilary body
What are the names of constriction and dilation of iris. what kind of control is this under
- Constricting (miosis)
- dilating (mydriasis)
- autonomic control
What are the functions of the ciliary body?
- Production and drainage of aqueous
humour - Anchors the lens via zonular fibres
- Changes the size and shape of the lens
through contraction and relaxation of the ciliary body muscles
What is the name and function of the posterior uvea
- Choroid
- lies between sclera and retina. highly vascularised and pigmented.
- provides blood supply to deep layers of retina
- tapetum Lucidum structure within = increases night vision in animals = greenish reflection =
Lens
- job: reflect light by changing shape
- Sits behind iris, attached to ciliary process by zonular fobres
- transparent to allow it to transmit light
- shorter, fatter lens = close vision
- longer thinner = distance
What is accommodation
How contraction or relaxation of the lens changes the depth of focus
what is the retina
- the neural layer that converts light into action potentials
- innermsot layer of the wall of the posterior segment
- 4 main cell types: outside = retinal pigment epithelium, photoreceptor cells (rods and cones), bipoalr ganglion, inside = multipolar ganglion
What are the structures visible in the posterior segment of the eye via an ophthalmoscope known as
- Ocular fundus
- includes optic disc, retina, retinal pigment epithelium, choroid including tapetum, sometmes sclera
3.
species differences
- position of orbit within skull: predators more rostrally, prey laterally
- Cats very little sclera, horses lot
- Horses = lacrimal caruncle in medial canthus of eye
- Rabbits one lower lacrimal punctum: other = dorsal and ventral
- ungulates = horizontal oval shaped cornea = wider horizontal field of vision vs round cornea of carnivores
- ungulates = oval pupil, cats upright slit shaped, pigs and dogs rounded. depends on where constrictor muscle lies
- Fundus- dog optic disc vaguely triangular, white fuzzy outline (myelination of ganglion cell axons). Horse and guinea pigs = tiny blood vessels, rabbits= white band across retina