Heterophoria/Convergence Insufficiency Flashcards
(32 cards)
What is the definition of heterophoria?
When the eyes are dissociated, a latent squint becomes manifest. Eyes are straight when both open.
What is convergence excess?
Deviation angle is larger at near
What is divergence weakness?
Deviation is larger at distance
What is non-specific esophoria?
No significant difference between deviation size at different distances
What is convergence weakness?
Larger deviation angle at near
What is divergence excess?
Larger deviation at distance
What is non-specific exophoria?
No significant difference of deviation size between distance and near
What are some common aetiologies for vertical deviations?
Congenital vertical muscle palsies
Thyroid eye disease
What does it mean if a phoria is compensated?
Px has enough fusional reserves to maintain BSV without lots of effort
What does it mean if a phoria is decompensating?
Lots of effort is being made to maintain BSV.
Sometimes controlled, but not all the time.
Likely eye strain and headaches, blurred vision, intermittent diplopia.
What does it mean if a phoria is decompensated?
Completely broken down - no control over phoria and unable to fuse.
Has turned into tropia.
What are some causes of decompensation?
Uncorrected or undercorrected RE (accomm needed so FRs struggle)
Poorly fitting specs cause poor image quality
Aniseikonia (can’t cope if new, e.g. cat op)
Poor GH (reduced FRs)
Head trauma
Drugs
Change in visual demands
How can a decompensating phoria be managed?
Appropriate RE correction
Orthoptic exercises
Prism
Botox
Surgery
How would you prescribe for someone with a decompensating esop who is hyperopic?
Full rx to reduce accommodative effort and so deviation size
How would you prescribe for someone with a decompensating esop who is myopic?
Full rx - undercorrecting would compromise VA/induce progression of myopia
How would you prescribe for someone with a decompensating exop who is myopic?
Undercorrect to reduce deviation size by inducing accommodation
What do orthoptic exercises aim to do?
Increase fusion range
How does a near stereogram work?
Used for exop to exercise positive convergence
Card at arms length
Fixate on target in front of card, inducing physiological diplopia
How does a distance stereogram work?
Used for esop to exercise negative convergence
Card at arms length
Fixate on target behind card, inducing physiological diplopia
When should you prescribe prism?
If px symptomatic and they relate to the decompensation
Try fresnel first (may be only option if large)
Prescribe the smallest amount that reduces sxs
How does botox work?
Overacting muscle paralysed - causes incomitant deviation
Angle is overcorrected to account for botox wearing off
Repeated every 4-6 months
Who is offered botox?
Angle too small for surgery but wants more than a prism
When is surgery offered?
Large deviation does not allow fusion
What can predispose someone to primary convergence insufficiency?
Wide PD
Excessive uniocular work undertaken
Little to no close work
