Strabismus Flashcards
Role of orthoptics
- Visual development in children and amblyopia
- Identification and mx of strabismus before surgery
- Eye movement disorders
Amblyopia
Lazy eye - reduced visual acuity in the absence of any structural cause or ocular disease
How to test visual acuity
Snellen chart
logMAR chart
How to perform a Snellen test
- Ask patients if they wear glasses or contact lenses
- Stand 6 metres or 3 metres using a mirror
- Cover one eye and read lines
- If can’t read, use pin point
- If still can’t read, move forward
- If still can’t read, use fingers
- If still can’t read, use hand movements
- If still can’t read, use light
How to interpret a Snellen chart
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
Snellen chart and logMAR comparison
6/60 = 1.0 6/12 = 0.3 6/6 = 0.0
LogMAR advantages
Decrease size in a standard format
Same number of letters on each row
Minimum visual acuity for driving
6/12
How to assess visual acuity in babies and young children
Keeler preferential looking cards - 8 weeks - 12 months
Cardiff acuity cards
Kay pictures
LogMAR Keeler book
Purpose of the cover test
Detect the presence of a manifest or latent deviation
Latent deviation
Squint that is not obvious unless an alternate cover test is done
Manifest deviation
Can see quint just by observing and using a cover uncover test
Associated signs with strabismus
Head tilting (away from lesion)
Ptosis
Nystagmus
Unequal pupils - when shining light (corneal reflections)
Esotropia
Inwards strabismus
Exotropia
Outward strabismus
Hypertropia
Upwards strabismus
Hypotropia
Downwards strabismus
Strabismus mimics
Horners syndrome
Physiological eye folds
How to carry out a cover test
- Corneral reflection symmetry using a pen torch
- Hold target at eye level, cover one eye and reveal
- Swap eye
- Test with and without glasses
Why does amblyopia occur
Cortical adaptation due to abnormal binocular environment e.g.
- strabismus
- anisometropia
- high refractive bilateral error
- stimulus deprivation - ptosis
- high astigmatism
Anisometropia
Interocular difference in refractive error - using one eye more than the other
Concomitant strabismus
Strabismus is the same regardless of where the patient is looking
Causes of concomitant strabismus
Children:
- Refractive error
- FHx
- Prematurity
- Developmental delay
- idiopathic
orthoptic assessment
Visual acuity - Snellen/logMAR
Cover test
Ocular movement test (H test)
Investigations for strabismus
Orthoptic assessment
Cycloplegic refraction
Fundoscopy
Slit lamp
Cycloplegic refraction
Paralyse lens to prevent compensatory accommodation reflex
Red flag signs for strabismus
Severe headache
Dizziness
Nause and vomiting
Amblyopia and strabismus management
- Glasses for refractive adaptation
- If visual acuity not equal, use patch at 4 - 5 yo to improve vision in weaker eye
- Once vision is equal and squint still apparent, surgery suggested
Incomitant strabismus
Different with different areas of gaze
Causes of incomitant strabismus
Cranial nerve palsies
Thyroid eye disease
Myasthenia gravis
Trauma/ orbital mass
Types of diplopia
Monocular
Horizontal binocular diplopia
Vertical binocular diplopia
Oblique binocular diplopia
How to test for monocular vision
Whilst covering one eye, diplopia persists
Causes of monocular vision
Cataracts
Uncorrected refractory error
How to test for binocular vision
Whilst covering one eye, the diplopia goes away
Driving with diplopia
Should not drive
Why do people with childhood strabismus not have diplopia
Retinal suppression
