Accomodation

Question 1

What mechanisms is the oculomotor system comprised of?

2

Answer 1

Accommodation and Vergence

Question 2

What can happen if one of the components of the oculomotor system is disrupted?
(2)

Answer 2

Amblyopia and or strabismus

Question 3

What state is the accommodation system in an emmetrope viewing a distant object?
(1)
Where will the image be focussed?
(1)

Answer 3

Relaxed - 0D power

Accurately on the retina

Question 4

What is the young eye able to do and what is this called?

3

Answer 4

It is able to alter is power for closer distances to be viewed clearly,
Ocular accomodation

Question 5

What are the three components of the accommodation mechanism?
(3)

Answer 5

1. Crystalline lens
2. Zonules
3. Ciliary Body

Question 6

What is the crystalline lens?
(1)
Where is it located?
(1)

Answer 6

A transparent, biconvex body

Situated between the iris and the vitreous

Question 7

What is the typical diameter of the lens?
(1)
What is the radius of curvature of the anterior surface?
(1)

Answer 7

9-10mm

8-14mm

Question 8

What are the three components of the lens?

3

Answer 8

1. Lens Capsule
2. Lens Epithelium
3. Lens Fibres

Question 9

What is the lens capsule?

1

Answer 9

A highly elastic structure enveloping the lens body

Question 10

What is the lens epithelium?
(1)
Where is it located?
(1)

Answer 10

A single layer of cubical cells (1)

Lie on the anterior lens body directly inside the capsule (1)

Question 11

What are the lens fibres?

2

Answer 11

Lens fibres constitute the body of the lens and stretch in arcuate fashion from the anterior to posterior pole of the lens

Question 12

What are the zonules and what do they do?

3

Answer 12

The zonules form a ring of delicate filaments which hold the lens in position, allowing changes in the volume of the ciliary muscle to be translated to the lens during accomodation

Question 13

What is the ciliary body?
(1)

Where does it start and end?
(1)

Answer 13

An annular structure extending from the ora serrata posteriorly to the iris root anteriorly

Question 14

What are the three types of ciliary muscle fibre and where do these start and end?
(6)

Answer 14

1. Longitudinal fibres - scleral spur to choroid
2. Radial fibres - scleral spur to ax’s of eye through ciliary body
3. Circular fibres - form a sphincter in the most axial portion of the muscle

Question 15

Describe the parasympathetic inner action of the ciliary muscle
(8)

Answer 15

Mediated - parasympathetic stimulation from edinger Westphal nucleus in CN3

Linked to nerve activity inducing vergence and pupillary constriction

Efferent pathway for accommodation arises in Brodmann area 19

Nerve fibres pass through internal corticotectal tract to hypothalamus to edinger Westphal nucleaus

Question 16

Describe the sympathetic inner action to the ciliary muscle

6

Answer 16

Arise in hypothalamus

Nerve fibres travel down spinal cord to ciliary centre of budge

Fibres continue to synapse in superior cervical ganglion from where a nerve travels to the ciliary body