Secondary Strabismus - MEH Flashcards
What is a secondary / sensory strabismus?
1.Occur following temporary or permanent impairment of VA
2. Vision loss may be Unilateral or bilateral
3. Normally Severe vision loss
How does the squint occour?
The loss of vision will cause a obstacle for sensory fusion therefore partially or completely disrupt fusion causing the eye to deviate
Px has had visual impairment between the age of 6 months - 7 years, what squint do they have and why?
Esotropia - accom and convergence is most active at these ages
Px has had visual impairment occurs at birth or older then 8 years, what squint do they have?
Exotropia
Is there a link between the degree of VI and development of exo/eso?
No
What causes secondary squints?
- Anisometropia / Aphakia
- Cataract
- Trauma
- Corneal opacity
- Macular lesions
- Glaucoma
- Optic atrophy
- Retinoblastoma (always watch out for in children, look for milky reflex)
- Secondary to sight saving surgery : repair for RD ect
How do we assess these px?
- Case History
- VA : likely to have a extremally reduced vision in both or one
- Fundus exam and media exam will indicate the VA
What are the orthotopic investigations we need?
Cover test : appropriate size target and if the visions are so low then we need to assess via corneal reflections
Measuring the angle :
1. Prism reflection test
2. Krimsky test
3. Hirschberg’s test : 1mm = 15PD/7degrees
When to assess for BSV?
If the secondary squint developed after 2 years,
Only if VA allows
This is important for surgery and sadly unlikely to restore
How do we assess the risk of diplopia?
Post operative diplopia test.
How do we treat ?
1.Treat the Vision loss : RX and amblyopia(strabismic/stimulus deprivation)
2. Restore alignment of the eyes : surgical intervention to restore alignment of the eyes) Use Botulinum toxin
3.Conservative management : Use of prisms (rare) and intractable diplopia
What is the aim of strabismus surgery?
To restore alignment of eyes.
What should we consider when operating for strabismus surgery?
The risk of post operative diplopia
When do we aim to leave the px slightly undercorrected?
Esotropia
When do we aim to leave the px overcorrected?
Exotropia
Which eye do you perform on first?
on the deviating eye
Is future strabismus surgery or Botulinum toxin therapy highly probable after surgery?
yes, as the possibility of restoring normal fusion is low
What can be used to see post operative risk?
BTXA :
Eso : inject medial rectus
Exo : inject lateral rectus
Can go home on same day
How effective is BTXA
3 months ; temp
IS there a limit with the number of injects we give ?
No
What works well for low angle strabismus?
BTXA
What can we do if the px has intractable diplopia?
- occlusive Cl
- Frosting of glasses lens (bangerton)
- Corneal tattoo
- Intraocular occlusive lens
- Prism ; shift the image into area of VF loss
What instrument can be used to measure the angle of deviation in the distance?
Synoptophore using corneal reflections
How is a prism reflection test carried out?
- assess corneal reflections
- place prism bar over DEVIATING eye
- increase prism bar strength until CRs are symmetrical
what type of patients is the krismsky test used for?
Px with poor vision
How is the krismsky test carried out?
- assess corneal reflections
- place prism bar over FIXATING eye
- increase prism bar strength until CRs are symmetrical
what is difference between krimsky compared to the prism reflection test?
prism bar is placed over fixating eye for krimsky, prism bar is placed over deviating eye for PRT
what is intractable diplopia?
unable to fuse images at all
