HETEROPHORIA AND STRABISMUS Flashcards
Why do we need the vergence system?
To allow the eye to function normally
To allow eyes to function under stress
To help with breakdown - if vision gets double
What is the difference between latent and manifest?
If latent it is heterophoria and not visible under normal BV conditions - this can be comfortably managed
If manifest it is a strabismus or a squint which is visible all the time
What is heterophoria?
- It is a latent misalignment of visual axes
- Functional BV still exists - motor and sensory
- May or may not produce stress and symptoms for the px
What are the classifications of a phoria:
Convergence insufficiency?
- Exophoria greater at near than distance
- Reduced positive fusional vergence reserves & NPC often accompany
What is the vergence compensation mechanism?
How the vergence system copes with misalignment tendency by using fusional vergence reserves as a compensation mechanism
What is fusional vergence reserve?
This includes initial disparity - driven response to heterophoria.
Fusional reserve measures how much additional vergence capacity is available before motor compensation mechanism break down
How do you measure fusional reserve?
Using a prism until a px with BSV reports target blur or diplopia
Base out (positive) - stimulates convergence
Base in (negative) - stimulates divergence
You can record blur/break/recovery points in prism dioptres
What is a strabismus?
A manifest alignment of visual axes.
Breakdown of BV system - motor and sensory.
Fully functional BV does not exist.
Primary visual axes are not aligned with each other.
Diplopia and confusion can occur as well as loss of fusion and stereopsis.
What is the frequency of misalignment with strabismus?
Can be constant - present at all times but can cause unwanted sensory consequences such as amblyopia.
Can be intermittent - present some of the time
fusion and BSV occur at other times and can include decompensation patterns.
What is the laterality of misalignment for a strabismus?
Unilateral - one eye is always misaligned and the other eye preferably fixates when both eyes are open
Alternating - either eyes fixates comfortably. Misaligned eye readily swaps
Forced alternation - either eye can hold fixation but break fusion
What is the comitancy of strabismus?
Concomitant is when strabismus magnitude does not change with gaze direction.
Non-concomitant is when strabismus magnitude does change with gaze direction
What happens when the strabismus is fully accommodative?
Strabismus is fully corrected with added lenses.
Accommodative esotropia.
Divergence excess exotropia (distance).
AC/A ratio high or uncorrected hyperopia
What happens with partially accommodative strabismus?
Strabismus is partially corrected with added lenses.
The magnitude reduces but BSV not reliably attained.
What happens with non-accommodative strabismus?
Strabismus magnitude does not change with added lenses
Why is the alternating cover test done?
To assess whether any movement is discernible.
To determine the direction of misalignment.
If there is no movement, no further CT is indicated
