Secondary Strabismus - MEH

Question 1

How to do classify strabismus?

Answer 1

• Primary
• Consecutive
  Secondary

Question 2

What is a secondary/sensory strabismus?

Answer 2

1. This is following VA impairment
2. Vision loss can be bi/unilateral and normally a high amount

Question 3

What is the process of developing secondary strabismus?

Answer 3

1. 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)

Question 4

What ages do eso and exo tend to manifest?

Answer 4

1. Esotropia = 6 months to 7 years ; this is when acc and conv is most active
2. 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 )

Question 5

What are the some causes of secondary strabismus?

Answer 5

1. Anisometropia
2. Congenital glaucoma
3. Macular lesions
4. Optic atrophy
5. Retinoblastoma (milky white reflex)
   Following a RD surgery

Question 6

How can we assess these patients?

Answer 6

1. History! - note previous trauma, surgery ect
2. VA - we are expecting a lower VA
3. Fundus and macula examination - this will indicator the level of visual acuity

Question 7

What Orthoptic investigation do we want to do?

Answer 7

1. 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
2. Prism reflection test / Krimsky test / Hirschberg test
3. 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.
4. Risk of diplopia test : correct px with a prism bar and then report when they have diplopia.*

Question 8

How many dioptres does 1mm of displacement mean?

Answer 8

This will equivalent of 15PD (prims dioptres)

Question 9

How do we manage px with secondary strabismus?

Answer 9

1. Treat the cause of vision loss : manage the amblyopia / refractive error
2. Restore the alignment of the eye : Use Botox / surgery
3. Conservative management : prisms
4. Intractable diplopia ; corneal tattoos, CL ect

Question 10

How does strabismus surgery work?

Answer 10

1. The aim is align the eyes again.
2. We should consider the risk of post operative diplopia

Question 11

If the px is esotropic do we leave the px over or under corrected?

Answer 11

Slightly under corrected ; this will be because of ours naturally diverge as we get older

Question 12

What considerations do we need to make with strabismus surgery?

Answer 12

1. Initial surgery is always on the deviating eye.
2. Adjustable strabismus surgery for tine tuning for px with blind. Severe sight impairment
3. We need to consider for future surgery/ BOTOX.

Question 13

Once strabismus surgery is done, what are the chances they will need it again?

Answer 13

High! Because we have a low chance of restoring normal fusion –> the squint will come back .

Question 14

Why would we use BTXA?

Answer 14

1. Diagnostically
2. Therapeutically
   (both are temporary)

Question 15

How can we use them therapeutically?

Answer 15

See the post operative risk of surgery!

Question 16

Which muscles are we injecting BTXA into ?

Answer 16

Eso = inject medial rectus
Exo = inject lateral rectus

Question 17

How long does this last and is there a limit on how many you can have?

Answer 17

Average amount of time is 3 months and no limit!

Question 18

How does BTXA actually work?

Answer 18

Stops the muscles from working! Inject the lateral rectus… the medical rectus will still work and pull it in!

Question 19

If the px has a large squint (45 dioptres) do we inject one eye or both?

Answer 19

Both eyes!!
Example:
1. Large exotropia, of 45 dioptres
2. We inject lateral rectus in both eyes!

Question 20

NOTE to Self :

Answer 20

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 :)

Question 21

Let’s say a px has had a few surgery’s on their squinted eye, what might we need to consider now?

Answer 21

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.

Question 22

What is intractable diplopia?

Answer 22

This is when the px cannot fuse the images at all.

Question 23

What can we do for intractable diplopia?

Answer 23

1. Frosting lens
2. Optical adaptions ; increasing or decreasing the rx to introduce blur
3. Intraocular occlusive lens
4. Corneal tattoo
5. Therapeutic CL
6. Prisms : this will make the vision blur. OR on a smarter note, we can displace the image into a visual field loss!

Question 24

Px with intractable diplopia had surgery but still has diplopia after, why is this?

Answer 24

The surgery was more so the for alignment of the eyes, and not helping with diplopia.