The eye and visual system Flashcards
What does stereopsis mean?
Seeing in 3D
The 3 layers of the eye
Outer layer - sclera and cornea
Middle layer - uvea
Inner layer: retina
Sclera and cornea transparency
Sclera is white, made up of collagen fibres that are cross fibred so opaque.
Cornea is extension of cornea but is transparent to allow light in. Cornea fibres of collagen are parallel.
Limbus
Area where sclera and cornea meet. Stem cells here.
Function of sclera
Protection and maintains spherical shape
Choroid
Blood supply and nutrition to retina.
Made of melanocytes.
Is coloured to prevent scatter of light entering eye.
Can have melanoma of the eye.
Retina
Transducer, takes image you see and turns it into electrical signal.
Ora serrata - after this area cannot receive light as no more photoreceptors.
Outer layer
Sclera - tough fibrous outer coat, collagen
Cornea - collagen
Light transmission -must be transparent
Barrier to trauma and infection, must be tough
Responsible for 2/3 refractive power of eye
Lens
Never stops growing,
Becomes less pliable,
With age, less ability to see things up close (age related long sighted ness is called Presbyopia)
The Outer Later
Epithelium
Bowman’s layer
Stroma
Descemet’s layer
Endothelium
(epithelium can grow back, but endothelium does not grow back so leads to vision loss)
What does the endothelium do?
1 cell thick
Keeps cornea dehydrated, pumps water out of stroma, keeps it transparent.
Middle Layer (uveal tract)
Uveal tract has 3 parts - choroid, ciliary and iris.
Choroid is blood supply to outer third of retina
Anything anterior of lens is anterior segment. Has chambers (anterior and posterior divided by iris).
Anterior segment filled with aqueous humor (made in ciliary body, moves through pupil to anterior chamber) maintains pressure of eye.
Drains at angle between iris and cornea.
If build up of pressure then can effect nerves.
Inner layer
Retina, specialised organ of phototransduction, may layer.
Outer retina has photoreceptor cells, chemical reaction, synapses with other cells to send signal to occipital lobe.
Rods and cones
Cones - colour perception, high resolution
Rods - shape and shades of grey, lower resolution
Macula lutea responsible for central vision, clarity. Fovea at centre of macula - highest visual acuity point.
Diabetes can cause damage
Pathway
Photoreceptors –> bipolar cells –> ganglion cells (all these axons merge and form optic nerve).
Supporting cells
Amacrine cells involved with first synapse
Horizontal cells involved with second synapse
Phototransduction
Light photons cause chemical change in rods and cones.
Within photoreceptors, vitamin A derivative is transformed and then recycled through enzyme.
Emmetropia
20/20 vision
Myopia
Short sighted (so can see near but not far, refractive power too high, overpowered so can’t focus on far objects on retina)
Get a minus lens to focus image on retina
Hypermetropia
Far sighted (so cannot see near, refractive power too low, underpowered to focus on near objects )
Get a plus lens
Could be due to shallow corneal curvature
Lens inflexibility
Axial length of eyeball too short
Adnexae
Lids, conjunctiva, tear film
Lids - protect globe
Anterior skin
Eye lashes
Meibomian glands
Orbicularis oculi
Tarsal plate
Tarsal conjuctiva
Levator palpebrae superioris and sympathetic muscle
Conjunctiva
Palpebral (on bottom eyelid part)
Bulbar (on eye)
Contains goblet cells and lymphoid cells for protection
Tear film
3 layers: anterior lipid
middle aqueous
posterior mucous
Protective and nutrition for cornea
Blood supply
Inner 2/3 retina = central retinal artery
Branches to super, inferior, temporal and nasal branches.
