Choroid Ciliary Body Iris

Question 1

What are the strands which suspend the lens in place

Answer 1

Zonules, suspensory ligaments

Question 2

What re the zonule fibres composed of

Answer 2

Non collagenous and composed of FIBRILLIN for elasticity

Question 3

Where do the zonules attach to

Answer 3

They run through the ciliary processes of pars plicata and pars plana and join on dentures along the ora serrata

Question 4

What structure anchors the zonules on the floor between the ciliary processes

Answer 4

Tension fibres; they allow the zonules to change direction 90 degrees

Question 5

What is accommodation

Answer 5

Accommodation is the ability for the eye to rapidly increase its refractive power to bring near objects into focus, I.e. converging image on the retina from behind

Question 6

Describe the ways how humans accommodate

Answer 6

Changing its lens power
Elongating the size of the eyeball
Change corneal curvature
Making lens multifocal
Moving lens along the axis

Question 7

Which way do humans tend to accommodate

Answer 7

Through altering the power of the lens, changing refractive power

Question 8

What are the biomechanics when there is contraction of longitudinal and circular ciliary muscles

Answer 8

Lens has a wider axial length
Anterior portion of lens is more curved and bulbous
Zonules fibres are lax

Question 9

What controls the ciliary muscle

Answer 9

The autonomic nervous system , parasympathetic branch

Question 10

How is accommodation controlled

Answer 10

Edinger westphal nucleus, which contains preganglionic parasympathetic neurones innervated by oculamotor nerve, synapsing in ciliary ganglion, causing ciliary muscle to contract

Question 11

How does the body know how much accommodation is required

Answer 11

The edinger westphal nucleus receives information from the supraoculomoter area which received direct input from the visual cortex

The visual cortex uses cues to determine how much accommodation is needed

Question 12

Near triad system of the edinger westphal nucleus

Answer 12

Accommodation, increasing refractive power
Pupil constriction, increasing the depth of field

Convergence, to ensure the second focal point lies on the fovea

Question 13

What is the diameter and depth of the anterior chamber

Answer 13

11.3-12.4mm in diameter and 3 mm in depth

Question 14

What is the aqueous humour responsible for

Answer 14

Nutrition of the avascular lens and cornea, as well as removing metabolic waste products

Question 15

Describe the pathway of the aqueous humour from production to drainage

Answer 15

It is produced by the unpigmented epithlium of the pars plicata, travelling from the posterior to the anterior chamber supplying lens and cornea with nutrients, then drained at the iridocorneal angle at the a canal of schlemm

Question 16

Describe briefly the mechanism of aqueous production

Answer 16

Ions are actively transported from the Stroma to the pigmented epithelium, then via gap junctions to the Non pigmented epithelium, the actively transported to the posterior chamber

Question 17

What is the role of adenylate cyclase in regulation of aqueous production

Answer 17

Adenylate cyclase is what causes the catalytic conversion of ATP to cyclic AMP, alpha agonists activate AC, and hence reducing the IOP, whereas beta agonists, inhibit action of AC, increasing IOP

Question 18

Is the uveoscleral pathway pressure independent or depend

Answer 18

Pressure independent, meaning that even if the IOP is low, in some cases, drainage will still occur, I.e. if metabolic waste products need to be eliminated

Question 19

What is the step a of the iris composed of

Answer 19

Loose areolar connective tissue, allowing the iris to easily change shape controlling pupil size

Question 20

Which segment of the iris contains the highest vascular system

Answer 20

Stroma

Question 21

Function of clump cells

Answer 21

Ingesting melanocytes and debris from epithelial cell death, clean up to keep aqueous free of debris

Question 22

Name the two muscles in the iris

Answer 22

Sphincter and dilator

Question 23

Function of dilator muscle

Answer 23

To increase size of pupil, pupil dilates as the radial dilator muscles contract

Question 24

Why does the iris contain tight and gap junctions

Answer 24

This is due to the fact that the length of each muscle spindle isn’t long enough to span from the iris root to pupil margin

Question 25

Function of the iris sphincter

Answer 25

This is to constrict the size of the pupil, miosis, as the circular sphincter muscles contract, they cause the pupil to shorten, in bright light especially

Question 26

Is the main blood supply for the iris

Answer 26

Major iridic circle

Question 27

Which part of the brain innervates pupil constriction

Answer 27

Edinger westphal nucleus of the midbrain via oculamotor nerve

Question 28

Where does the outer retina receive its bloody supply and nutrients from

Answer 28

The choroid, choriocapillaris

Question 29

What is drusen and its consequences

Answer 29

Drusen essentially are a set of debris composed of proteins and lipids, its function is to push the photoreceptor layer away from the choriocapillaris, hence starving the photoreceptors of essential nutrients
Linked with AMD