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)
