Anatomy & Physiology of the Eye Flashcards
Draw and label a picture of the eye?
Find one on google images
What are the contents of the orbit?
The eye Extra-ocular muscles Cranial nerves II - VI Arteries and veins Orbital fat
There are 3 layers to the eye, what are they?
Fibrous: outermost layer, cornea and sclera
Vascular layer: choroid, ciliary body, iris
Inner layer: innermost layer, retina
Describe the fibrous layer of the eye?
What are the functions of this layer?
Cornea and sclera
Cornea is the transparent bit that covers the front of the eye (iris, pupil).
It refracts light onto lens.
Sclera is the fibrous white layer that covers the rest of the eye. It provides attachments for the extra-ocular muscles
Describe the vascular layer of the eye? What are the functions of this layer?
Choroid: a layer of connective tissue and blood vessels which provides nourishment to retina
Ciliary body: smooth muscle fibres which surround the posterior chamber (which surrounds the iris) and are attached to the lens. They control shape of lens and contribute to formation of aqueous humor.
Iris: ring shaped, containing smooth muscle fibres which alter diameter of pupil. It sits in front of the lens
Describe the inner layer of the eye?
What are its functions?
The retina
Which has two layers:
- Pigmented layer
- outer layer
- attached to choroid
- supports neural layer - Neural layer
- inner layer
- contains photoreceptors
What is meant by the ‘non-visual retina’?
Anteriorly, the pigmented layer extends further than the neural layer does.
So this part is non-visual because there’s no neural layer, so there are no photoreceptors
What are important structures of the retina?
Macula: the centre of the retina, which is yellow-ish
Fovea: a depression in the macula, which contains only cones and is for high acuity vision
The optic disc: where the optic nerve enters retina, no photoreceptors are here
There are two ‘chambers’ in the eye. What are they where are they located?
Anterior and posterior chambers
Fluid filled areas
Anterior chamber: between cornea and iris
Posterior chamber: between iris and ciliary processes
What fluid fills the anterior chamber of the eye?
Where is this fluid produced and drained?
What’s the significance of this?
Aqueous humor: a clear plasma like fluid which nourishes and protects the eye
It’s produced constantly by the ciliary body and drained via trabecular meshwork
If drainage is obstructed, glaucoma can result
What is the difference between aqueous and vitreous humor?
Aqueous: in the anterior and posterior chambers
Vitreous: clear gel which fills up space between lens and retina
What’s the blood supply and venous drainage of the eye?
Internal carotid artery > Ophthalmic artery > many branches
Most important branch is the retinal artery
Drainage: superior and inferior ophthalmic veins, which drain into cavernous sinus
What are the two types of photoreceptors? Describe them and their function?
Rods and cones
Rods:
- vision at low light
- peripheral retina and so peripheral vision
- little-no colour vision
Cones:
- vision in good light
- densely packed in fovea (no rods)
- colour vision
Describe what happens to allow you to see something?
Light reflects from the source onto the object
These light waves then enter the eye.
The cornea refracts the light onto the lens
The lens refracts the light onto the retina
The retina contains rods and cons which absorb photons (light) triggering a change in membrane potential of rod or cone.
This then sends an action potential to the optic nerve and then to the brain for it to be processed.
What’s the innervation of all the extra-ocular muscles?
LR - 6 (abducens)
SO - 4 (trochlear)
The rest are 3 (oculomotor)
What do these muscles do to the eye?
SR
IR
LR
MR
SO
IO
SR: elevate eye
IR: depress eye
LR: abduct eye (away from midline)
MR: adduct eye (toward midline)
SO: depress + abducts eye (down and out)
IO: elevate and abducts eye (up and out)
Which extra-ocular muscle elevates the eyelid? Which nerve supplies it?
Levator palpebrae superioris
Oculomotor
Describe the pathway of a nerve impulse from the eye to the brain to be processed?
Passes down optic nerve
Gets to optic chiasm: where it either decussates or doesn’t
Goes down optic tract
To the lateral geniculate nucleus
Which splits into optic radiations
The nerve impulse passes down one of these to the visual cortex in the occipital lobe where it’s processed
Then
Draw out a diagram showing how some nerve impulses decussate at the optic chiasm and some don’t.
Light/vision in periphery of visual field lands on the nasal retina
Impulses from the nasal retina decussate at optic chiasm
Light/vision in centre of visual field lands on the temporal retina
Impulses from temporal retina do not decussate.
Explain why a tumour pressing on the optic chiasm causes bitemporal hemianopia?
Bitemporal hemianopia is loss of vision in the outer half of the right and left visual field
Light waves from peripheral vision land on the nasal retina
Impulses from the nasal retina decussate at the optic chiasm.
If a tumour is pressing on the optic chiasm, this will affect ability of nerve impulses that are decussating to pass.
If they can’t pass, no impulses will be able to go from nasal retina to the visual cortex
So no peripheral vision.
Which nerves control the pupils.
What is the posh name for constriction and dilation of pupil?
The autonomic nervous system
Constriction (miosis) is controlled by parasympathetic nervous system
Dilation (mydriasis) is controlled by sympathetic nervous system
What is miosis and myadriasis?
Miosis: pupil constriction (parasympathetic)
Myadriasis: dilation (sympathetic)
