Heterophoria and convergence insufficiency Flashcards
What is the definition of a heterophoria?
Latent squint - eyes are straight when binocular, but the visual axes deviate when the eyes are dissociated.
What is convergence excess?
Larger deviation angle at near (eso)
What is divergence weakness?
Larger deviation angle at distance (eso)
What is convergence weakness?
Larger deviation at near (exo)
What is divergence excess?
Larger deviation at distance (exo)
What is a non-specific phoria?
No difference in deviation size at different distances
What is a hyper/hypophoria?
Vertical deviation of the eyes on dissociation
What are some common aetiologies of hyperphoria?
Congenital vertical muscle palsies
TED
What is a compensating phoria?
BSV maintained with minimal effort due to sufficient fusional reserves.
If longstanding large phoria, increased FRs may develop.
What is a decompensating phoria?
Lots of effort is being put into maintaining BSV.
Eyestrain results if excessive effort.
Tropia results when fusion breaks but will fusion will return.
What is a decompensated phoria?
Fusion is completely broken down, not able to re-fuse, so tropia now constant.
What can cause decompensation?
Uncorrected or inaccurate correction
Poor fitting specs
New aniseikonia (e.g. post cat)
Poor GH causing reduced FRs
Head trauma
Drugs
Change in visual demands
What tests can be done to investigate a decompensating phoria?
Refraction
Fundus and media
History
VA
CT at both distances + PCT
Motility
Convergence
Accommodation
Fusion
Stereopsis
Hess
Diagnostic occlusion
What are the conservative methods of managing decompensating phoria?
Correct refractive error appropriately
Orthoptic exercises e.g. stereograms
Prism
What refractive correction should you give to a hyperopic px with ESOP?
Full rx
Reduces accommodative effort
What refractive correction should you give to a px with EXOP?
Consider undercorrection
Induces accommodation/convergence to reduce EXOP size/encourage fusion
What refractive correction should you give to a myopic px with ESOP?
No undercorrection
Compromises VA
What do near stereograms help to control?
EXOP
Use positive relative convergence
How should near stereograms be used?
Card at arms length
Fix on target in front of card.
Physiological diplopia induced, 2 middle images will fuse
What do distance stereograms help to control?
ESOP
Use negative relative convergence
How should distance stereograms be used?
Card at arms length
Fix on target behind card.
Physiological diplopia induced, 2 middle images will fuse
When should prism be prescribed? What other considerations should be made?
If px is symptomatic, and they are related to the decompensation.
Only prescribe the smallest amount needed.
Fresnel may be a good inital option to see if works (or may be only option if large deviation)
What are the invasive methods of managing decompensating phoria?
Botox
Surgery
Why would botox be used as a treatment for decompensating phoria?
Angle too small for surgery but needs more than a prism
