Lens and fundus Flashcards
Where does the lens sit?
Behind iris at anterior
Attached to vitreous at posterior
What suspends the lens?
Zonular fibres from ciliary processes
What is the purpose of the lens?
Focus light on the retina
What is the lens reliant on?
Transparency
Stable position
Ability to change shape
What does the lens consist of (4 parts)
Acellular capsule
Cortex of lens fibres
Central nucelus
Anterior epithelium
What creates transparency in the lens?
Arrangement of lens fibres in the cortex
What can be found where lens fibres meet? When are they more apparent?
Y-shaped suture lines
In cataracts
What is a cataract? What causes it?
Cloudy lens
Disruption of lens fibres (in cortex)
What is the function of the anterior epithelium of the lens?
Maintains hydration
Produces lens fibres
The lens is avascular. How does it obtain nutrients and get rid of waste?
Via aqueous humour
Change in aqueous humour = change in lens
What is the fundus of the eye?
Part of the posterior segment viewed with an opthalmasocpe
What structures of the fundus are visible?
Optic disc
Retina
Retinal pigmented epithelium
Choroid
Light must pass through several layers of the retina before reaching rods and cones. What assists with transparency?
Unmyelinated axons
What are the layers of the retina?
Retina pigmented epithelium (outermost)
Axons of ganglia innermost
Retinal blood vessels supply the inner retinal layers. What are these layers?
Nerve fibre layer
Ganglion cell layer
Inner plexiform layer
Where do axons become myelinated in the retina?
At optic disc
What is the name of the area with most cone cells? Where is it near?
Area centralis
Near optic disc
What is the area of the retina with most ganglion cells? Where is it?
Visual streak
Same place as area centralis
What is the function of the retinal pigmented epithelium
Phagocytose old photoreceptors
Vitamin A metabolism
Move metabolites in and out of retina
What is the optic disc between in a dog?
Tapetal and non-tapetal fundus
Where is the optic disc in the cat?
Within the tapetal dundus
Where is the optic disc in large animals?
Within the non-tapetal fundus
Is the optic disk light or dark? Which species is the exception?
Light
Cats - dark pink due to no myelin
What is the difference of the blood supply of the neuroretina in cats and dogs?
Dogs more tortuous
Cats straighter
How can arteries and veins be distinugished in the neuroretina? Which species is it difficult to see retinal vessels?
Arteries narrower than veins
Horse
What do birds lack in their fundus?
No pigment
No tapetum lucid
No retinal blood vessels
What do birds have additionally in their fundus? What is this? What does it do?
Pecten
Projection of choroid into posterior chamber
Helps diffusion of nutrients to retinal cells
