Strabismus

Question 1

Role of orthoptics

Answer 1

1. Visual development in children and amblyopia
2. Identification and mx of strabismus before surgery
3. Eye movement disorders

Question 2

Amblyopia

Answer 2

Lazy eye - reduced visual acuity in the absence of any structural cause or ocular disease

Question 3

How to test visual acuity

Answer 3

Snellen chart

logMAR chart

Question 4

How to perform a Snellen test

Answer 4

1. Ask patients if they wear glasses or contact lenses
2. Stand 6 metres or 3 metres using a mirror
3. Cover one eye and read lines
4. If can’t read, use pin point
5. If still can’t read, move forward
6. If still can’t read, use fingers
7. If still can’t read, use hand movements
8. If still can’t read, use light

Question 5

How to interpret a Snellen chart

Answer 5

6/6 +2

• Numerator = distance from board
• Denominator = line they can read
• Indices = extra letters they can read

6/6 means they can see what the average population sees at 6 metres

Question 6

Snellen chart and logMAR comparison

Answer 6

6/60 = 1.0
6/12 = 0.3
6/6 = 0.0

Question 7

LogMAR advantages

Answer 7

Decrease size in a standard format

Same number of letters on each row

Question 8

Minimum visual acuity for driving

Answer 8

6/12

Question 9

How to assess visual acuity in babies and young children

Answer 9

Keeler preferential looking cards - 8 weeks - 12 months

Cardiff acuity cards

Kay pictures

LogMAR Keeler book

Question 10

Purpose of the cover test

Answer 10

Detect the presence of a manifest or latent deviation

Question 11

Latent deviation

Answer 11

Squint that is not obvious unless an alternate cover test is done

Question 12

Manifest deviation

Answer 12

Can see quint just by observing and using a cover uncover test

Question 13

Associated signs with strabismus

Answer 13

Head tilting (away from lesion)
Ptosis
Nystagmus
Unequal pupils - when shining light (corneal reflections)

Question 14

Esotropia

Answer 14

Inwards strabismus

Question 15

Exotropia

Answer 15

Outward strabismus

Question 16

Hypertropia

Answer 16

Upwards strabismus

Question 17

Hypotropia

Answer 17

Downwards strabismus

Question 18

Strabismus mimics

Answer 18

Horners syndrome

Physiological eye folds

Question 19

How to carry out a cover test

Answer 19

1. Corneral reflection symmetry using a pen torch
2. Hold target at eye level, cover one eye and reveal
3. Swap eye
4. Test with and without glasses

Question 20

Why does amblyopia occur

Answer 20

Cortical adaptation due to abnormal binocular environment e.g.

• strabismus
• anisometropia
• high refractive bilateral error
• stimulus deprivation - ptosis
• high astigmatism

Question 21

Anisometropia

Answer 21

Interocular difference in refractive error - using one eye more than the other

Question 22

Concomitant strabismus

Answer 22

Strabismus is the same regardless of where the patient is looking

Question 23

Causes of concomitant strabismus

Answer 23

Children:

• Refractive error
• FHx
• Prematurity
• Developmental delay
• idiopathic

Question 24

orthoptic assessment

Answer 24

Visual acuity - Snellen/logMAR
Cover test
Ocular movement test (H test)

Question 25

Investigations for strabismus

Answer 25

Orthoptic assessment Cycloplegic refraction Fundoscopy Slit lamp

Question 26

Cycloplegic refraction

Answer 26

Paralyse lens to prevent compensatory accommodation reflex

Question 27

Red flag signs for strabismus

Answer 27

Severe headache Dizziness Nause and vomiting

Question 28

Amblyopia and strabismus management

Answer 28

1. Glasses for refractive adaptation 2. If visual acuity not equal, use patch at 4 - 5 yo to improve vision in weaker eye 3. Once vision is equal and squint still apparent, surgery suggested

Question 29

Incomitant strabismus

Answer 29

Different with different areas of gaze

Question 30

Causes of incomitant strabismus

Answer 30

Cranial nerve palsies Thyroid eye disease Myasthenia gravis Trauma/ orbital mass

Question 31

Types of diplopia

Answer 31

Monocular Horizontal binocular diplopia Vertical binocular diplopia Oblique binocular diplopia

Question 32

How to test for monocular vision

Answer 32

Whilst covering one eye, diplopia persists

Question 33

Causes of monocular vision

Answer 33

Cataracts | Uncorrected refractory error

Question 34

How to test for binocular vision

Answer 34

Whilst covering one eye, the diplopia goes away

Question 35

Driving with diplopia

Answer 35

Should not drive

Question 36

Why do people with childhood strabismus not have diplopia

Answer 36

Retinal suppression