BV 4 - deviation variables
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What are the 9 deviation variables?
- 1. Direction
- 2. Frequency
- 3. Magnitude
- 4. Laterality
- 5. Dominance
- 6. ACA
- 7. Cosmesis
- 8. Variability
- 9. Comitance
- intermittent % at dx and near
- observe before disassociation
- angle of deviation at primary angle
- far and near
- control accom- full rx, use accom target
maybe one eye used for dx and one for near?
- determines if strab has accom component
- accomm may decrease deviation
- may determine what rx to give
Factors favourable for ST and unfavourable for XT?
- +ve Lambda angle
- narrow nose bridge
- absence of epicanthus
- large PD
- narrow face
Factors favourable for XT and unfavourable for ST?
- -ve angle lamba
- wide nose bridge
- wide face
- presence of epicanthus
- small PD
Factors that suggest non-comitance
- abnormal head position - usually towards affect muscle
- version underaction - test duction
- alternating CT in diff DAF
How to differentiate if there is a mechanical obstruction or not?
- version testing - issue
- duction testing:
- a) no issue - not mechanical
- b) issue - mechanical
When do you use a Park's 3 step test and what is a disadv?
- When a vert deviation is noted
- only works if one muscle is affected
L hyper in primary gaze, hyper worse in R gaze, hyper worse with L head tilt. What muscle is affected?
What is an alternating CT in 9 DAF and what to watch out for?
- test for incomitance and magnitude
- watch out for prismatic effect of specs
What is a Hess Lancaster chart?
- confirms diagnosis of paretic muscle
- can confirm if more than one muscle affected
- quantifies deviation
What tests are available determine if there is a deviation?
- listening to parents
- direct observation
- 4BO prism test
- uni and alt CT
What is angle lambda?
angle between the pupillary axis and line of sight
What is a positive angle lambda?
nasal corneal reflection
- comparing corneal reflection when shining a torch infront of px 33-100cm away
- symmetrical and equal = no/small deviation
- 1mm displacement = 22PD
Hirschberg: OD +0.5mm OS -1mm
- 0.5mm nasal deviation in OS
- 11PD LST
What is the Krimsky test?
similar to hirschbirg but placing prism infront of the nondeviating eye to reposition corneal reflex of deviating eye to same relative position as nondeviating eye
Adv of krimsky?
can perform on blind or deep amb
What are the disad of CT?
- cant use on blind/deep amb- suppression
- contaminated by EF
- will not usually reveal a microtropia
Why can you not use unilateral to measure magnitude?
- you will not measure full amount of deviation
- they may be using fusional conv/diverg
XT, diverg excess and CT?
- do test in a hall way/6m room
- usually problems in the far dx
What is a primary angle?
- the amount of deviation when the non-paretic eye is fixating
- the prism will be placed over the paretic eye
What is the secondary angle?
the amount of deviation when the paretic eye is fixating
When might there be a difference between the primary and secondary angle?
When incomitance is present, the secondary angle will be larger than the primary angle. This occurs when the good eye is occluded and the deviating eye is forced to pick up fixation - alot more innervation is required and hence the yoked muscle in the good eyes is deviated much more.
What is the minimum difference between the primary and secondary angle to consider the prescence of incomitance?
>9PD or 5deg
What is the phi test?
- subjective alternating CT
- keep adding prism until px responds that image doesnt move
How and why and when is a 4BO test used?
- to detect microtropias
- use if decreased VA in one eye and no movement on CT
What would you see in 4BO test in a normal BV px?
- 1. prism over OD: OU both version away from base
- 2. OS vergence movement towards base
- 3. Same if prism over OS
What would you see with a microtropia (ST) in 4BO test (say OD is normal)?
- 1. Prism over OD: OU version away from base
- 2. No vergence of OS
1. Prism over OS: No movement
- useful for microstrab
- fundus reflex
- brighter eye = deviating eye
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