C: Eye

Question 1

What 4 structures does light have to pass through before reaching the retinal photoreceptors in the eye?

Answer 1

1) Cornea
2) Aqueous humour (Anterior and posterior chambers)
3) Lens
4) Vitreous body
Retinal photoreceptors

Question 2

What and where is the conjunctiva?

Answer 2

Epithelium which covers the exposed part of the sclera and inner surface of the eye lids

Question 3

What is the function of the conjunctiva?

Answer 3

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

Question 4

What is the function of the sclera?

Answer 4

Tough protection from injury, supports eye and provides attachment for the extraoccular muscles which move the eye

Question 5

What is the function of the iris?

Answer 5

Contains the dilater pupillae and sphincter pupillae muscles - acts as an adjustable diaphragm which regulates the amount of light reaching the retina

Question 6

What is the nerve supply to the circular muscle of the iris ie. the sphincter pupillae muscle?

Answer 6

Parasympathetic nerves via the ciliary ganglion
Presynaptic - occulomotor nerve CN3
Post synaptic - V1 (ophthalmic)

Question 7

What is the nerve supply to the ciliary muscle contained within the ciliary body?

Answer 7

Parasympathetic fibres via the ciliary ganglion
Presynaptic = oculomotor CN3
Post synaptic = V1 (ophthalmic)

Question 8

What effect does contraction of the ciliary body have upon the lens?

Answer 8

Muscle contracts - tension on the suspensory ligament is reduced, so the lens assumes a more convex position

Question 9

What are cataracts?

Answer 9

Abnormal opacification of the lens leading to loss of visal acuity and when severe, blindness

Question 10

Other than its involvement in controlling the shape of the lens, what is the other function of the ciliary body?

Answer 10

Production of aqueous humour which fills the anterior compartment of the eye

Question 11

What is the function of the aqueaous humour which fills the anterior compartment of the eye?

Answer 11

Pressure of this fluid helps to maintain the shape of the cornea and thus the refractive properties of the eyes

Question 12

Through what structures is aqueous humor absrobed back into blood stream?

Answer 12

Through the canal of schlemm at the irido-corneal angle

Question 13

Problems with drainage of aqueous humour can lead to what?

Answer 13

Glaucoma

Question 14

What is glaucoma?

Answer 14

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

Question 15

Give 2 functions of the choroid layer of the eyeball?

Answer 15

1) Provides support to retina

2) Heavily pigmented thus absorbing light which passes through the retina

Question 16

What does the retina line?

Answer 16

Most of the posterior compartment of the eye (ie, the area posterior to the lens and ciliary body)

Question 17

What 3 things does the retina contain?

Answer 17

1) Photoreceptors
2) First order neurons of the visual pathway
3) Secondary order neurons of the visual pathway

Question 18

What 2 parts is the retina made up of?

Answer 18

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

Question 19

What are the 6 main cell types of the retina?

Answer 19

1) Pigmented epithelial cells
2) Rod cells
3) Cone cells
4) Bipolar cells
5) Interneurons
6) Ganglion cells

Question 20

What are the 3 functional differences between rod and cone cells?

Answer 20

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

Question 21

Where do the axons of the retinal ganglion cells run in the retina?

Answer 21

Run over the inner surface of the retina to converge on the optic disc/papilla where they turn outwards to form the optic nerve

Question 22

Why does the optic papilla/disc form a blind spot on the retina?

Answer 22

There are no photoreceptors at the optic papilla

Question 23

What is papilloedema?

Answer 23

Inflammed optic disc

Question 24

What is papilloedema a sign of?

Answer 24

Raised intraocular pressure

Question 25

How does papilloedema arise?

Answer 25

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

Question 26

Give 2 other causes of swelling of the optic disc in addition to raised ICP?

Answer 26

1) Infection of the optic nerve

2) Autoimmune inflammation

Question 27

What is the macula lutea?

Answer 27

Yellow pigmented zone just lateral to the optic disc

Question 28

What lies at the center of the macula lutea?

Answer 28

A specialised area called the fovea

Question 29

What is the fovea?

Answer 29

The point on the retina at which the image of the object at the center of the visual axis falls

Question 30

In what 4 ways is the fovea specialised for visual acuity?

Answer 30

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

Question 31

What is a detached retina, why is it important for a detached retina to be repaired ASAP?

Answer 31

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

Question 32

Give 3 functions of the aqueous humour which is secreted by the ciliary bodies into the anterior chamber?

Answer 32

1) Source of nutrients for the non vascular lens
2) Optical medium which is non refractive with respect to the cornea
3) Pressure of aqueous humour maintains shape of cornea