Week 1.07 Associated Phorias Flashcards

1
Q

What does fixation disparity mean

A

Fixation disparity refers to a small misalignment of the eyes during binocular vision, where the images from each eye do not fall on exactly corresponding points of the retina

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2
Q

What is exo and eso disparity

A

Exo disparity - axes slightly divergent (rel to fixation)
ESO disparity - axes slightly convergent (rel to fixation)
Vertical disparity also occurs

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3
Q

What is the difference between phoria and fixation disparity

A

Phoria: measurement of deviation when fusion is suspended (dissociated conditions)
FD: minute misalignment when fusion is present and active (normal binocular conditions)

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4
Q

What does the term associated phoria mean

A

Prism named to neutralise FD sometimes termed the associated phoria should

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5
Q

Measuring FD

A

Usually measured using haploscopic principle
- presenting target or each fovea separately to indicate direction of visual axes - so one target to left and one the right at same time and rest of visual field is a natural scene promotes fusional response
- usually done with polarised light/filters
- but needs fusion lock - central vs peripheral

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6
Q

Mallet unit and FD

A

A mallet unit is a measurement used in the assessment of fixation disparity. It is a part of a binocular vision test that helps quantify the degree of misalignment (or disparity) between the two eyes when they are aimed at the same visual target

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7
Q

Prism neutralisation in FD

A

What we do with the mallet unit is find the point where prism is neutralised and FD has gone to zero and that is the associated phoria

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8
Q

Ideal parameters for FD measurement

A
  • Normal visual environment
  • Central and peripheral fusion locks
  • Enables detection of small disparities
  • Monocular markets that are not easily suppressed
  • Monocular markers close to central fixation point
  • Can detect horizontal and vertical fixation disparities
  • Easily understood by px
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9
Q

What should you do if px has an AP?

A

Should only address by anomaly or a suspected by anomaly if the px has symptoms
Two options: orthotics or prescribe prism

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10
Q

How to treat exo associated phoria

A

Weakest base in to eliminate slip
Or modify rx in -ve direction (I.e over-minus or under-plus) stimulate accommodation
Don’t rule out oprthoptic exercises

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11
Q

How to treat eso associated phoria

A

Weakest base out prism to eliminate slip
Or modify rx by adding +ve lens power relax accommodation, unlikely to help at distance but may be possible at near
Don’t rule out orthoptic exercises

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12
Q

How to treat vertical associated phoria

A

Eliminate any horizontal slip
Check optical centres on specs
Check head postures
Any residual vertical slip use prism

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13
Q

Prism adaptation

A

If precerive prisms leave in place for 10 minutes
Adaptation may take place
I.e. after 10-20mins, AP which has neutralised has now returned
Don’t prescribe prism if adaptation has taken place

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