Physiology - Vision

Question 1

How would you describe the sclera and cornea?

Answer 1

Tough connective tissue continuous with the dura

Question 2

What is the visible sclera and what is it covered by?

Answer 2

White of the eye

Covered with conjunctiva membrane

Question 3

What is the cornea and its function?

Answer 3

Transparent

Responsible for 2/3 of eye total refraction

Question 4

What is the function of the ciliary muscle?

Answer 4

Controls lens shape (accommodation for near visions)

Question 5

What is the function of the iris?

Answer 5

Defines pupil diameter (light reflex)

Question 6

What secretes acqueous humor?

Answer 6

Ciliary body

Question 7

What is the difference between aqueous and vitreous humour?

Answer 7

Aqueous humour - water like, anterior chamber

Vitreous humour - jelly like, posterior chamber

Question 8

What is the function of the choroid?

Answer 8

Blood supply for the receptor cell (deep) layer of the retina

Question 9

Describe the supply of the retina.

Answer 9

Internal layer has retinal blood vessels (blood supply for middle and superficial layers of retina from central retinal artery, enters via optic disc)
Outer part of retina relies on choroid (receptor layer)

Question 10

What is special about the fovea?

Answer 10

No blood vessels at fovea, relies on choroid for diffusion of oxygen and glucose (do not want BV to obstruct view since the fovea has the greatest visual acuity)

Question 11

List some examples of disorders with typical retinal appearances.

Answer 11

Damaged from raised intraocular pressure (glaucoma) - pressure in front of eyeball
Increased vascularization in diabetes
Bulging of optic disc (papilloedema) in raised ICP (increased pressure behind eyeball)

Question 12

What is the difference between conjugate and convergence gaze?

Answer 12

Conjugate gaze - eyes move together

Convergence - squint/come together

Question 13

Describe the movements of the eyes.

Answer 13

Altering fixation - moves in saccades
Smooth pursuit - fixed on moving target
At rest - microsaccades, constant motion on retina, not fixed

Question 14

Describe how images change when formed on the retina.

Answer 14

Images formed on the retina are upside down and reduced (inverted and switched left/right)

Question 15

What adjusts the lens and why?

Answer 15

Ciliary body for accommodation

Question 16

What is the name given to the stiffening of the lens with age?

Answer 16

Presbyopia - less able to accommodate

Question 17

Describe what controls the shape of the lens.

Answer 17

Contraction state of the ciliary muscles determines the amount of tension that the zonular fibres exert on the lens.

Question 18

Describe the contraction state of the ciliary muscles and lens shape.

Answer 18

Contracted ciliary muscle = lower tension on zonular fibres and more rounded lens
Relaxed ciliary muscle = higher tension on zonular fibres and more flattened lens

Question 19

List the processes occurring with near vision.

Answer 19

Accommodation
Convergence
Pupillary constriction

Question 20

Describe the process of near vision.

Answer 20

Increased firing of parasympathetic nerves to ciliary muscle
Contraction of ciliary muscle
Relaxation of zonular fibres
Relaxation of the lens so that it becomes more spherical
Near objects brought into focus

Question 21

What is wrong in nearsightedness vs farsightedness?

Answer 21

Nearsightedness - eyeball too long

Farsightedness - eyeball too short

Question 22

What causes glaucoma?

Answer 22

Drainage canal becomes blocked or extra aqueous humor is produced resulting in increased eye pressure
Increased eye pressure causes damage to the blood vessels and optic nerve
Optic nerve looks caved in/cupped

Question 23

Describe the characteristic pattern to loss of visual field - scotoma.

Answer 23

Rim of optic nerve becomes thinner as disc caves in and becomes more cupped.