Secondary Strabismus - MEH Flashcards
How to do classify strabismus?
- Primary
- Consecutive
Secondary
What is a secondary/sensory strabismus?
- This is following VA impairment
- Vision loss can be bi/unilateral and normally a high amount
What is the process of developing secondary strabismus?
- Loss of vision = hard to fuse images.
(This lack of fusion can be partial or full and both will cause the effected eye to deviate)
What ages do eso and exo tend to manifest?
- Esotropia = 6 months to 7 years ; this is when acc and conv is most active
- Exotropia = At birth - 6 months or older than 8 years old.
(There is no link to amount of VI and development of eso and exo )
What are the some causes of secondary strabismus?
- Anisometropia
- Congenital glaucoma
- Macular lesions
- Optic atrophy
- Retinoblastoma (milky white reflex)
Following a RD surgery
How can we assess these patients?
- History! - note previous trauma, surgery ect
- VA - we are expecting a lower VA
- Fundus and macula examination - this will indicator the level of visual acuity
What Orthoptic investigation do we want to do?
- CT - make sure the size is appropriate (the visions are going to be lower remember!). PX may not be able to take up central fixation = use corneal reflections
- Prism reflection test / Krimsky test / Hirschberg test
- Level of BSV : we will do this if the squint comess on after 2 years old. Px needs to be able to see to do this.
- Risk of diplopia test : correct px with a prism bar and then report when they have diplopia.*
How many dioptres does 1mm of displacement mean?
This will equivalent of 15PD (prims dioptres)
How do we manage px with secondary strabismus?
- Treat the cause of vision loss : manage the amblyopia / refractive error
- Restore the alignment of the eye : Use Botox / surgery
- Conservative management : prisms
- Intractable diplopia ; corneal tattoos, CL ect
How does strabismus surgery work?
- The aim is align the eyes again.
- We should consider the risk of post operative diplopia
If the px is esotropic do we leave the px over or under corrected?
Slightly under corrected ; this will be because of ours naturally diverge as we get older
What considerations do we need to make with strabismus surgery?
- Initial surgery is always on the deviating eye.
- Adjustable strabismus surgery for tine tuning for px with blind. Severe sight impairment
- We need to consider for future surgery/ BOTOX.
Once strabismus surgery is done, what are the chances they will need it again?
High! Because we have a low chance of restoring normal fusion –> the squint will come back .
Why would we use BTXA?
- Diagnostically
- Therapeutically
(both are temporary)
How can we use them therapeutically?
See the post operative risk of surgery!
Which muscles are we injecting BTXA into ?
Eso = inject medial rectus
Exo = inject lateral rectus
How long does this last and is there a limit on how many you can have?
Average amount of time is 3 months and no limit!
How does BTXA actually work?
Stops the muscles from working! Inject the lateral rectus… the medical rectus will still work and pull it in!
If the px has a large squint (45 dioptres) do we inject one eye or both?
Both eyes!!
Example:
1. Large exotropia, of 45 dioptres
2. We inject lateral rectus in both eyes!
NOTE to Self :
Although BTXA can be used for large squints..
BTXA is the best for treating small angle squints.
Also, if you made it this far keep going :)
Let’s say a px has had a few surgery’s on their squinted eye, what might we need to consider now?
Doing surgery on their better seeing eye –> px needs to be supported and well informed on this as it can arise some anxiety doing surgery on their good eye.
What is intractable diplopia?
This is when the px cannot fuse the images at all.
What can we do for intractable diplopia?
- Frosting lens
- Optical adaptions ; increasing or decreasing the rx to introduce blur
- Intraocular occlusive lens
- Corneal tattoo
- Therapeutic CL
- Prisms : this will make the vision blur. OR on a smarter note, we can displace the image into a visual field loss!
Px with intractable diplopia had surgery but still has diplopia after, why is this?
The surgery was more so the for alignment of the eyes, and not helping with diplopia.