Non-Surgical Strabismus Management

Question 1

What prism do you use to correct Eso?

Answer 1

Base Out

Question 2

What prism do you use to correct Exo?

Answer 2

Base In

Question 3

What prism do you use to correct Hyper deviations?

Answer 3

Base Down

Question 4

What prism do you use to correct Hypo deviations?

Answer 4

Base Up

Question 5

What prism stimulates convergence?

Answer 5

Base Out

Question 6

What prism stimulates divergence?

Answer 6

Base In

Question 7

What is Hering’s Law?

Answer 7

When the contralateral eye moves in in response to the ipsilateral eye having a Base In prism and then moves out again to regain fusion (fusional divergence)

Question 8

What options are there for non-surgical management of strabismus?

Answer 8

1) Orthoptic exercises
2) Modifying refractive correction
3) Prisms
4) Botulinum Toxin (botox)

Question 9

What is the aim of non-surgical management of strabismus?

Answer 9

Achieve good, well maintained BSV at all distance & is useful when there’s a delay in surgery or for those who refuse or are unfit for surgery

Question 10

Why would you use orthoptic exercises?

Answer 10

As a non-surgical management of strabismus.
1) Eliminate suppression
2) Control a deviation
3) Extension of fusional amplitude
4) Improve relative (functional) convergence
5) Improve near point of convergence

Question 11

What do you need to be aware of in orthoptic exercises?

Answer 11

Compliance is essential and regular breaks are needed
That people should wear refractive correction and must have BSV
For BSV check that physiological diplopia is appreciated if pathological diplopia isn’t

Question 12

What are Prism Bar Exercises?

Answer 12

A form of orthoptic exercise for non-surgical management of strabismus. The aim is to improve fusional amplitudes & is a makeshift bar of Fresnel Prisms. At each visit prism fusion range is completed with an increase in Fresnel strength gradually.

Question 13

What are Bar Reading Exercises?

Answer 13

A form of orthoptic exercise for non-surgical management of strabismus. The aim is to improve controlled binocular acuity (CBA) which is the maximum visual acuity obtainable while maintaining BSV irrespective of uniocular VA. It involves manipulating accommodative and vergence systems. It’s used to improve near CBA in accommodative eso

Question 14

What is CBA (controlled binocular acuity)?

Answer 14

The maximum visual acuity obtainable while maintaining BSV irrespective of uniocular visual acuity (previously CBA was known as BVA)

Question 15

What are the two outcomes of the bar reading exercises?

Answer 15

The bar is raised so either eye is able to read what’s below the bar. The patient will see either of 2 thing:
1) Fusion
Physiological diplopia occurs: 2 of the red bar then fusion occurs where the text is single and the patient can “see through” the bar

2) Suppression
Suppression occurs: red bar blocks the text

Question 16

What is the method of the bar reading exercises?

Answer 16

If BSV they can see the print behind. You can then reduce the print size until they’re unable to read it (like in manifest strabismus, diplopia or suppression)
The print may become blurred if unable to accommodate appropriately whilst controlling deviation

Question 17

How do you do Controlled Binocular Acuity (CBA) as an orthoptic exercise?

Answer 17

1) Participant reads down a letter chart at the required distance
2) The examiner observes ocular alignment
3) The end-point is:
The patient becomes manifest or the patient has reached their maximum level of visual acuity whilst maintaining control

Question 18

What are the outcomes expected of CBA exercises?

Answer 18

For some, clarity is important and so will become manifest earlier and so the CBA exceeds acuity of the weaker eye

Others sacrifice clear vision to gain BSV so the end point is less than uniocular VA when the patient asked to try to make the chart clear again, the deviation may become apparent

It’s the balance between accommodation and convergence. The max VA obtainable whilst maintaining binocular single vision

Question 19

How can orthoptic exercises help achieve accommodation and convergence?

Answer 19

In Eso accommodation may be relatively less than ‘normal’ to maintain BSV
&
In Exo accommodation may be in excess of ‘normal’ (resulting in pseudo myopia) when the deviation is controlled

Question 20

What is negative relative convergence?

Answer 20

Convergence is relaxed in relation to accommodation exerted and is used to control eso deviations

Question 21

What is positive relative convergence?

Answer 21

Convergence is exerted in excess of accommodation and is used to control an exo deviation

Question 22

How can we improve negative relative convergence with stereograms?

Answer 22

Improved by fixing at a target at distance. The stereogram is held at 33cm whilst fixating in the distance resulting in crossed diplopia of 4 cats. The distance is then adjusted until the 3 cats are clearly seen by relaxing convergence to look through the card. This improves Eso deviations by accommodating more than converging

Question 23

How can we improve positive relative convergence with stereograms?

Answer 23

Improved by fixing at a target at near. The stereogram is held at 33cm whilst fixating on a pen that’s held between the eyes and the card. Causes uncrossed diplopia of 4 cats and distance is adjusted until 3 cats are clearly seen. This near position improves positive relative convergence and thus exo deviations as having to converge more than accommodate.

Question 24

What lens, prism and relative convergence do you use for Eso deviations?

Answer 24

Convex (+ve), Base Out, Negative

Question 25

What lens, prism and relative convergence do you use for Exo deviations?

Answer 25

Concave (-ve), Base In, Positive

Question 26

How do we use refractive correction as a non-surgical management of strabismus?

Answer 26

Essential to have prescription early in treatment; can modify prescription in similar way like when giving additional lenses. We always work off a baseline prescription but don’t compromise vision
(+ve in eso and -ve in exo)
Give minimum strength to achieve deviation control (tested through CT and CBA) and check the impact on VA with the aim to reduce additional lenses but it isn’t always possible to do

Question 27

What prescription would you give an emmetropic child with an intermittent distance XT?

Answer 27

Concave (minus)
e.g. -1.0 or -1.5

Question 28

What prescription would you give an emmetropic child with an ET at near?

Answer 28

Bifocals - Convex (+ve)
At near only with nothing for distance

Question 29

What prescription would you give a child with ET for near and distance with a -4.0 prescription?

Answer 29

A slightly reduced minus lens that doesn’t impact vision
e.g. -3.5 or -3.0

Question 30

How do Fresnel Prisms work?

Answer 30

Can be put on glasses or Plano glasses but they can cause blur, glare, distortion and <VA.
Give minimum strength for comfortable near BSV generally over eye with worst vision and can incorporate into glasses when at least 40 months stable

Question 31

What’s the largest Fresnel prism strength you can give?

Answer 31

40PD but the larger the prism, the higher the distortion & blur
But >20PD cannot be incorporated into glasses due to moving the optical centre of the lens and the heaviness but can continue to use some incorporation and combine with Fresnel prisms