Flashcards in C: Eye Deck (32):
What 4 structures does light have to pass through before reaching the retinal photoreceptors in the eye?
2) Aqueous humour (Anterior and posterior chambers)
4) Vitreous body
What and where is the conjunctiva?
Epithelium which covers the exposed part of the sclera and inner surface of the eye lids
What is the function of the conjunctiva?
secretes mucous which contributes to the protective layer on the exposed surface of the eye and allows the lids to move more freely over the eyes
What is the function of the sclera?
Tough protection from injury, supports eye and provides attachment for the extraoccular muscles which move the eye
What is the function of the iris?
Contains the dilater pupillae and sphincter pupillae muscles - acts as an adjustable diaphragm which regulates the amount of light reaching the retina
What is the nerve supply to the circular muscle of the iris ie. the sphincter pupillae muscle?
Parasympathetic nerves via the ciliary ganglion
Presynaptic - occulomotor nerve CN3
Post synaptic - V1 (ophthalmic)
What is the nerve supply to the ciliary muscle contained within the ciliary body?
Parasympathetic fibres via the ciliary ganglion
Presynaptic = oculomotor CN3
Post synaptic = V1 (ophthalmic)
What effect does contraction of the ciliary body have upon the lens?
Muscle contracts - tension on the suspensory ligament is reduced, so the lens assumes a more convex position
What are cataracts?
Abnormal opacification of the lens leading to loss of visal acuity and when severe, blindness
Other than its involvement in controlling the shape of the lens, what is the other function of the ciliary body?
Production of aqueous humour which fills the anterior compartment of the eye
What is the function of the aqueaous humour which fills the anterior compartment of the eye?
Pressure of this fluid helps to maintain the shape of the cornea and thus the refractive properties of the eyes
Through what structures is aqueous humor absrobed back into blood stream?
Through the canal of schlemm at the irido-corneal angle
Problems with drainage of aqueous humour can lead to what?
What is glaucoma?
Increased intra-ocular pressure due to obstruction to the drainage of aqueous humour from the eye whilst the ciliary body continues to secrete it - if untreated it can cause damage to the neural retina and can cause blindness
Give 2 functions of the choroid layer of the eyeball?
1) Provides support to retina
2) Heavily pigmented thus absorbing light which passes through the retina
What does the retina line?
Most of the posterior compartment of the eye (ie, the area posterior to the lens and ciliary body)
What 3 things does the retina contain?
2) First order neurons of the visual pathway
3) Secondary order neurons of the visual pathway
What 2 parts is the retina made up of?
1) An outer pigment layer - a single layer of cuboidal cells with melanin filled microvilli extending from their inner surface
2) A multi layered neural retina
What are the 6 main cell types of the retina?
1) Pigmented epithelial cells
2) Rod cells
3) Cone cells
4) Bipolar cells
6) Ganglion cells
What are the 3 functional differences between rod and cone cells?
1) Rods responsible for vision at low light (scotopic vision) whilst the cones are responsible for vision in higher light levels (photopic vision)
2) Rods dont mediate colour vision whilst cones are capable of colour vision
3) Rods have low spatial acuity whilst cones have high spatial acuity
Where do the axons of the retinal ganglion cells run in the retina?
Run over the inner surface of the retina to converge on the optic disc/papilla where they turn outwards to form the optic nerve
Why does the optic papilla/disc form a blind spot on the retina?
There are no photoreceptors at the optic papilla
What is papilloedema?
Inflammed optic disc
What is papilloedema a sign of?
Raised intraocular pressure
How does papilloedema arise?
Optic nerve is continuous with the subarachnoid space of the brain so increased intracranial pressure is transmitted through the optic nerve - the anterior end of the optic nerve stops abruptly at the eye, the pressure is assymetrical and this causes a pinching and protrusion of the optic nerve at its head
Give 2 other causes of swelling of the optic disc in addition to raised ICP?
1) Infection of the optic nerve
2) Autoimmune inflammation
What is the macula lutea?
Yellow pigmented zone just lateral to the optic disc
What lies at the center of the macula lutea?
A specialised area called the fovea
What is the fovea?
The point on the retina at which the image of the object at the center of the visual axis falls
In what 4 ways is the fovea specialised for visual acuity?
Modified to obtain the maximum photoreceptor sensitivity and is thus the area with the greatest visual discrimination:
1) At fovea inner layers are flattened laterally so as to present the least barrier to light reaching the photoreceptors
2) Retinal blood vessels are absent at fovea
3) Photoreceptors are almost exclusively cones which are elongated and closely packed
4) Neuronal interconnections in the bipolar cells provide 1:1 ratio of cone cells to optic nerve fibres meaning each foveal receptor is individually represented in the visual cortex
What is a detached retina, why is it important for a detached retina to be repaired ASAP?
A retina which becomes detached from the underlying choroid tissue at the back of the eye causing loss of vision in the affected area. The more severe the detachment and the longer it has been present then the less vision is expected to return hence it needs to be repaired quickly