Orthoptics I - Investigation of BSV

How do we assess controlled binocular acuity?

cover test
- manifest squint = no BSV response
- latent squint = if recovery is good, then BSV is present

How do we assess sensory fusion?

bagolini glasses
Worth 4 dot
polaroid 4 dot

How do we assess motor fusion?

20 prism test
prism fusion range

How do we assess stereopsis?

quantitative or qualitative
frisby, lang, fly

What other BSV tests are there?

synoptophore
4 prism test
sbisa bar

What is the aim of sensory fusion testing?

to establish the presence and type of diplopia
determine suppression
assess response to correcting prisms

What are the bagolini glasses?

striated lenses, causing lines of light to be perceived when looking at a spotlight
- least dissociative

How are bagolini glasses performed and interpreted?

with refractive correction and at 1/3m and 3m
BSV response would have one light, with two lines making an x
right eye diplopic/suppression response = one (or two) lights and one line going left
left eye diplopic/suppression response = one (or two) lights and one line going right

ask patient to scan left and right - sometimes the other line is too far over for them to see looking straight on

How may abnormal retinal correspondence manifest during a bagolini glasses test?

same as BSV but the x does not cross the spotlight

Describe Worths 4 dot test

more dissociative than bagolini glasses
red-green filter glasses at 33cm and 3m
different coloured lights perceived by each eye - how many lights, red or green?

If the patient sees only 2 red lights the response is...

left suppression

if the patient only sees 3 green lights the response is...

right suppression

if the patient sees 5 lights, with the RED on the RIGHT, the response is...

homonymous diplopia

If the patient sees 5 lights, with the RED on the LEFT, the response is...

heteronymous diplopia

Describe the 20D prism test for motor fusion

used in young children from 3-4 months onwards
use a near, accommodative target
introduce prism - eyes converge
divergence seen when prism is removed

patient should be able to overcome, the divergence movement is easier to see than the convergence

Positive relative vergence is...

convergence in excess of accommodation
- measured with BO prisms

Negative relative vergence is...

convergence relaxed relative to accommodation
- measured with BI prisms

What is motor fusion range measuring?

fusional amplitude
- full amplitude/break point = single vision irrespective of blurred/clear image
- relative vergence/blur point = single vision whilst maintaining clear image

What are the benefits of testing motor fusion range?

can establish how well a heterophoria is compensated
subjective AND objective
can be used to assess treatment progression

What factors influence PFR

target size (bigger = easier)
order of base direction (prism adaptation - measure the compensating range first)
testing speed (prism adaptation: vergence adaptation to retinal disparity and brings induced deviation back to baseline levels)
- need a consistent speed
prism bar positioning

What is the objective response to PFR?

seeing the px fail to overcome prism

What is subjective response to PFR?

report of diplopia

Typical near horizontal PFR

35/40BO - 15BI

Typical distance horizontal PFR

15BO - 5/7BI

Typical vertical PFR

3BU - 3BD

Typical cyclo PFR

3excyclo - 3incyclo

Define stereopsis

relative depth of objects on the basis of fixation disparity

When may stereopsis reach adult levels by?

7 months

Describe random dot stereotests

computer generated dots
form shape that are duplicated and shifted to create disparity
fusion of dots caused a stereopic effect

What is one advantage and one disadvantage of random dot stereotests?

less susceptible to monocular cues
difficult for poor VA

What is the synoptophore used for?

to assess all grades of BSV

What slides are used for what BSV grade in the synoptophore?

red = simultaneous perception
green = fusion slides
yellow = stereopsis

What is relative vergence?

vergence ability in respect to accommodation