Dr Kevin Houston

Talia Mouldovan

Interventions for vision

impairments post brain injury:

Use of prisms and exercises

Disclosures

Dr. Houston: EYEnexo LLC, EyeTurn app

Apps discussed are prototypes and are

not being promoted for sale.

Vision Rehabilitation

• Use of lenses, visual assistive devices,

therapies, environmental modifications

and strategies to enhance vision and

minimize functional impairments caused

by vision loss

Spaulding Rehabilitation Hospital Boston

Terminology

• Esotropia (deviated in)

• Exotropia (out)

• Hypertropia (up)

• Hypotropia (down)

Rates of Strabismus at Spaulding

• 110 cases

• August 2015 to March 2016

• Most common: CN III, IV, VI,

convergence insufficiency

Diagnosing Strabismus

• Cover Test with Prism Neutralization

• Hirschberg/ Krimsky test

Diagnosis: Motor Field Test

• Measure strabismus in different positions

of gaze

Ocular Convergence

• Activation of both medial recti to rotate

the eyes inward, typically for near

viewing

Diplopia, Visual Confusion, Rivalry, & Suppression

• Diplopia (Double Vision): Seeing the same object twice

• Visual Confusion (Overlapping images): Seeing different visual stimuli in the same visual direction

• Rivalry: Competition between the eyes when visual information does not match

• Suppression: Neurological process of actively inhibiting visual input from part of the vision, typically of one eye

Cranial Nerves Involved in Eye Movement

• CN III Palsy

– Signs: Lid down, pupil affected, eye down and out

• CN IV

– Signs: Head tilt, blurred vision, worse on downgaze, balance

• CN VI

– Signs: Worse at distance, cross eyed, head turn

What can you observe?

Strabismus Assessment Pearls

• The amount of strabismus can be very

small

• It may not be noticeable

• Patient may not report double vision

What is it

like to have

strabismus?

Normal

View

Exotropia =

double vision

&

visual

confusion

Illustration of Vertical Strabismus

• Reports Blurry Vision

• Closes one eye

• Dizziness and Imbalance

• Avoids Participating

• Tilting/turning head

Disadvantages of Patching

• Appearance

• ~20 degrees of peripheral vision loss

• May discourage recovery

• Affects Spatial Attention

• Patients are often not satisfied with this

approach

Other Treatments

• Prisms

• Vision Therapy

• Therapy + Prisms

• Surgery

Prism

A mystical optical element

splits light into component colors?

Ophthalmic Prisms Shift light instead of

focusing, color dispersion is minimal

Apex

Base

Direction of

image shiftLight

Image

If you look through a prism

Image shifted towards apex (thin side)

3.5 deg

base down

Direction of

image shift

Apex

Base

Designs of Prisms:

Standard Prism vs. Fresnel

Standard

Fresnel

Photo

illustratio

n next

slide

10 degree standard vs. 20 degree Fresnel

The Fresnel = an important advance for clinical application of prisms

Up to 30 degrees

Application for Strabismus

• Fit over entire lens of one eye to

optically align the images seen by the

two misaligned eyes.

Base Out

Base In

Prisms Facilitate Fusional

Convergence

Prisms: An assistive device for Strabismus

• Reduce the amount of fusional vergence

needed

• Fit over entire lens of one eye to optically

align the images seen by the two

misaligned eyes.

*Prisms for strabismus well accepted in mainstream

Ophthalmology/Optometry

Important to be aware of side effects

• All prisms cause chromatic aberration

and distortion

• Press-on prisms cause additional blur

(filmy vision)

• Lessened angle of strabismus is

sometimes more bothersome

– harder to ignore double image

– This is monitored closely

Actual Photo Through a 10 degree

Press-on Fresnel

Prism

View

Actual

View

Spaulding Vision Rehab

1) environmental adaptation & postural

adaptation to improve function;

2) neuro-muscular re-education with

oculomotor vision therapy to maximize

recovery

Patient with R CN III palsy: When she looks right (or postures with a left head turn)

she gets single vision

When she looks left (or postures with a right head turn) she gets double vision

Flowcharts for Postural Modifications

• Postural adaptations

3rd

Turn L

Turn R

Distance Easier,

Move Further

Distance Easier,

Move Further

Right Eye

Affected

Left Eye

Affected

6th

Turn R

Turn L

Move Closer

Move Closer

Right Eye

Affected

Left Eye

Affected

4thRight Eye

Affected

Left Eye

Affected

Bring reading material up

&/or tilt chin in

Tilt head L Tilt head R

Turn head L Turn head R

*Cue to focus hard to eliminate diplopia

*Cue to relax gaze to eliminate diplopia

Our eyes moves naturally, isn’t that enough?

• Avoidance with head posture

• Disuse syndrome of ocular muscles

• No attempted vergence

• Atrophy eventually

• *Disuse is not referring to amblyopia. Not a

concern in adults.

• Disuse refers to avoid making eye movement

into paretic field

Vision Interventions

• 3rd Nerve

• 4th Nerve

• 6th Nerve

• Binocular Impairments

• Hemianopia

Vision Exercises

• Oculomotor strengthening

• Improve fusion/single image

• Improve vergence

Oculomotor Strengthening

• Pursuits

– O, X, H

• Saccades

– Thumb saccades

https://eyetracking.com.sg/2016/05/16/eye-trackers-sampling-frequency/

Alternate Cover, Cover-UnCover

• Stabilize head in straight ahead position and look

at target (smaller targets are more difficult)

• Alternate covering each eye several times while

looking at a target

• Uncover both eyes and try to fuse into one image

http://nzhypnotherapy.co.nz/wp-

content/uploads/2017/09/eye-covered.jpg

Head Turns

Look at target (starts as double) and slowly

rotate head to move images closer

together to become single

Check the postural modification cheat sheet

– To determine which direction should lessen

the misalignment

https://www.prehabexercises.com/basic-

assessments-and-movement-evaluations-

for-runners/https://prezi.com/udrportonnz-/joints-of-

the-skeletal-system/?webgl=0

Vestibulo-Ocular Reflex

https://www.youtube.com/watch?v=yL7TBP8fBtg

http://www.strabismusworld.com/neurology-

physiology-psychology-vision/the-vestibular-system-

and-vision/

Vergence Exercises

• Pencil Push Ups

• Brock String

• Fusion Cards

ConvergenceDivergence

http://bio.vtn2.com/bio-

home/harvey/lect/lectures.html?ccode=fb&mda=scrn&flnm=fb

_sizedist&ttl=Size%20and%20distance

Brock String

Convergence or Divergence:

• Moving the x of the string closer and

further away

• Slow: slowly move the bead toward or

away from the nose

• Fast: jumping between looking at several

beads

http://www.bernell.com/product/BC109

/Brock-String-Devices

http://drboulet.com/brock-string-double-vision/

Free-space Fusion Cards

Lifesaver cards

https://www.youtube.com/watch?v=Ui3KTZOdzbo

Bottom Up Top Down

Vestibular Ocular

Reflex

Repetitive Head

Rotations Single to

Double

Alternate Cover

Repetition

Retinal Disparity/Refixation

Motor Priming

Repetitive

Saccades

(Head Stabilized)

Volitional FEF

to brainstem

Protocols: Oculomotor Therapy

OCULOMOTOR THERAPY GOALS:

1) Maximize Neuromuscular Recovery

2) Prevent Disuse Atrophy

3) Prevent Contracture

4) Motor Adaptation

5) Recruitment

6) Psychological Benefit

Frequency

• Wear prism glasses as often as possible

• Exercises ideally 3 sessions per week

for 30 minutes each

• 2 minute minimum per task or 60-100

reps

Troubleshooting

• Ensure binocularity– Are they blocking or closing one eye?

– Make sure both eyes are fixating

– Watch for suppression

• Avoid Compensation– Are they rotating their head when it should be stable?

• Find the best position before starting– Examples:

• Establish sight of a single pencil before bringing it closer

• Adjust head, string or bead position until they see the x of

the brock string

Questions?