Vision

Question 1

Define refraction

Answer 1

Light rays bend to form a sharp image on the retina

Question 2

Define accommodation

Answer 2

Changing the focus from distant to near objects

Question 3

What are refractive errors?

Answer 3

Mismatches between distance to retina and how much we bend the light rays, causing the image to be formed in the wrong place

Question 4

What process describes how we see?

Answer 4

Phototransduction

Question 5

What three things happen to comprise accommodation?

Answer 5

Lense changes shape (becomes thicker and more spherical)
Pupil constricts
Eyes converge

Question 6

How does the lense become thicker?

Answer 6

Ciliary muscles contract which makes the ciliary body bulge
This allows the suspensory ligaments to become lax
Lense is no longer being stretched so becomes thicker and more spherical

Question 7

What innervation causes ciliary body contraction and pupil constriction?

Answer 7

Parasympathetic innervation via the third cranial nerve (oculomotor nerve)

Question 8

Which muscle constricts the pupil?

Answer 8

Sphincter pupillae

- concentric muscle around the border of the pupil

Question 9

Which muscles contract to cause the eyes to converge?

Answer 9

Medial rectus muscles

Question 10

Which extrinsic eye muscle are thicker and why?

Answer 10

Medial recti muscles because we spend a lot of time doing close work

Question 11

Define myopia

Answer 11

Myopia: short-sightedness
Image is formed in front of the retina due to over-refraction or a too-short eyeball
Close objects look clear, distant objects look hazy

Question 12

Define Astigmatism

Answer 12

Astigmatism: non-spherical curvature of the cornea or lense

Question 13

Define presbyopia

Answer 13

Presbyopia: long-signtedness of old age

Question 14

Define hyperopia

Answer 14

Hyperopia: long-sightedness
Image is formed behind the retina due to under-refraction of light or a long eyeball
Close objects look hazy, distant objects look clear

Question 15

What are the symptoms of myopia?

Answer 15

Headaches
Complaining of not being able to see the whiteboard or distant objects etc.
Infants and preverbal children may develop a squint
Toddlers may lose interest in sports/people and be more interested in books/pictures
- may also lose interest in class if they can’t see the board

Question 16

What are the symptoms of hyperopia?

Answer 16

Symptoms of eyestrain after reading or working on the computer
Convergent squint in children/toddlers

Question 17

Define phototransduction

Answer 17

The conversion of light energy to an electrochemical response by photoreceptors (rods and cones)

Question 18

Where in the rod/cone cells are the photoreceptors?

Answer 18

In the outer segment

Question 19

What are the lamellae? Where are they located?

Answer 19

Cell membrane “disks” containing visual pigments

Located in the outer segment of the rod/cone cells

Question 20

Name the visual pigments and where they are found

Answer 20

Rhodopsin - rod cells

Cone Opsin S, M and L - cone cells

Question 21

What is Glaucoma? What is the main complication that it can cause?

Answer 21

Abnormally high intraocular pressure caused by a build up of fluid.
Blindness - nerve fibres die from the optic disk outwards

Question 22

Name the two types of Glaucoma

Answer 22

Chronic: Primary Open Angle Glaucoma
Acute: Angle Closure Glaucoma (this is a medical emergency)

Question 23

Describe the presentation of acute glaucoma (angle closure glaucoma)

Answer 23

Unilateral blurred vision accompanied by severe pain and a red eye.
Sudden onset (acute)
Patient may experience nausea and vomiting

Question 24

Describe the underlying mechanisms involved in angle closure glaucoma

Answer 24

Some event causes the peripheral iris to block the angle so that aqueous humour cannot drain:

1) functional black in a small eye with a large lense
2) mid-dilated pupil - iris periphery crowds around the angle and obstructs outflow
3) the iris sticks to the pupillary border which causes the iris to balloon anteriorly and obstruct the angle

Question 25

Describe the management of angle closure glaucoma

Answer 25

Decrease intraocular pressure
- IV infusion of carbonic anhudrase inhibitors
- constrictor eyedrops
- eyedrops of beta blockers and steroids
Analgesia
Laser iridotomy in both eyes

Question 26

Describe the clinical presentation of primary open angle glaucoma

Answer 26

Raised intraocular pressure
Visual field defects
Optic disk changes on opthalmoscopy

Question 27

What causes primary open angle glaucoma?

Answer 27

Blockage of the trabecular meshwork in the drainage angle, meaning that fluid cannot drain properly but is still being produced. The amount of fluid in the eye increases which causes intraocular pressure to also increase.

Question 28

Describe the management of primary open angle glaucoma

Answer 28

Eyedrops to decrease intraocular pressure
 - prostaglandin anologues
 - beta blockers
 - carbonic anhydrase inhibitors
Laser trabeculoplasty
Trabeculectomy surgery (last resort)

Question 29

Which parts of the eye make up the Uvea

Answer 29

ciliary body + iris + choroid

Question 30

List possible causes of uveitis

Answer 30

Isolated illness
Non-infectious autoimmune disease
- e.g. HLA-B27
Infectious disease
- tends to be chronic diseases such as TB
Systemic disease
- tend to be inflammatory e.g. ankylosing spondylosis

Question 31

Describe and explain the presentation of uveitis

Answer 31

Symptoms vary depending on location
Unilateral or bilateral depending on location
Inflamed blood vessels leak plasma and WBCs causing blurred vision
Can present with pain

Question 32

List the possible causes of a corneal ulcer

Answer 32

Infection - bacterial, viral, fungal

Trauma - trauma, corneal degeneration, dysrophy

Question 33

Describe the main features of non-inflammatory corneal disease

Answer 33

Mostly dystrophies
Bilateral, opacifying, genetically determined
May be due to accumulation of substances (e.g. lipids) within the corna