microtropia - MEH Flashcards
define microtropia
a constant small angle unilateral strabismus under 10 prism dioptres, presence of subnormal BSV
clinical characteristics of microtropia (7)
- manifest monocular strab 10^ or less
- anisometropia (commonly hypermetropia)
- amblyopia (reduced VA in the affected eye)
- abnormal BSV (reduced stereovision) and sensory and motor fusion
- may have foveal supression scotoma
- may have eccentric fixation
- can have NRC or ARC
can you get a small angle squint without BSV?? and is this a microtropia?
NO - main point of a microtropia is that px CAN achieve BSV
what are the 3 main causes of microtropia?
- anisometropia
- hereditary
- unknown
what is the most common cause of microtropia?
anisometropia
why is anisemotropia a cause of microtropia?
results in a defocused image to the more ametropic eye
what is NRC?
normal retinal correspondence - you do this with both eyes.
- nasal retina in 1 eye corresponds to temporal retina of the other eye
Nasal corresponding with temporal allows us to have binocular single vision
what is ARC?
abnormal retinal correspondence
- sensory adaptation to manifest strabismus to facilitate BSV
- fovea of 1 eye corresponds to an extrafoveal area of the other eye
- This is a binocular condition
Is eccentric fixation binoc or monoc condition?
monocular
what is eccentric fixation?
the eye fixates with an area outside the fovea
what are the sub classifications of eccentric fixation?
- parafoveal
- macular
- paramacular
- peripheral
do you get EF or ARC in microtropia?
can be both - depending on whether the eyes are viewing monoc or binoc
what are the 2 types of microtropia?
microtropia WITH identity
microtropia WITHOUT identity
Does the word “identity” refer to fixation or deviation in microtropia?
fixation
CT results for microtropia WITH identity
no manifest movement noted on cover/uncover
fixation in microtropia WITH identity
eccentric fixation = stable parafoveal fixation
in a microtropia WITH identity, what is the amount of eccentricity is equal to?
the angle of deviation. For an example if the squint is 6D this relates to 12 degrees ; this is where the eccentric fixation will be
what is the retinal correspondence in someone with a microtropia WITH identity?
ARC is present
do you have stereopsis with a microtropia WITH identity
gross stereoacuity
why is there no movement seen on cover/uncover in a microtropia WITH identity?
px is using parafoveal fixation therefore no change in fixation - they never use their actual fovea to view. The use parafovea binocular and monocularly
in a microtropia WITH identity, how is BSV appreciated?
ARC, no diplopia appreciated
CT results of microtropia WITHOUT identity
small manifest deviation noted on cover/uncover
large latent component may be noticed on ACT
where is the fixation with someone with microtropia WITHOUT identity
central fixation
in a microtropia WITHOUT identity, does eccentric fixation coincide with the angle of deviation?
no
retinal correspondence in someone with microtropia WITHOUT identity
ARC or NRC with central suppression scotoma
in someone with microtropia WITHOUT identity, how do they appreciate BSV? if the px has ARC
it will be harmonious ARC, therefore able to achieve BSV
Nr or grey dot corresponds to FI under binoc viewing
in someone with microtropia WITHOUT identity, how do they appreciate BSV? if the px has NRC
Expansion of panums fusional area
what is the secondary classification ?
primary and secondary
What is primary microtropia?
- Initial defect
- accompany other concomitant deviations
what are 2 types of secondary microtropia?
residual
seen after stabismus surgery ; such as surgery after infantile esotropia. We correct the esotropia to a microtropia
what are the 2 aims of investigation?
- diagnose the microtropia
- assess the quality of BSV (stereo and fusion)
how do the majority of px’s present with a microtropia?
- referred from failed vision screening (school or pre-school_
- referral from routine eye exam with defective vision
- constant or intermittent squint
why is family history important?
hereditary factor for microtropia
what does the vision vary from in microtropia?
0.2 to over 1.00 LogMAR
why do you need to use crowding when testing VA?
most accurate vision with crowded linear chart compared to single optotypes ; this is more real world viewing
what is affected when VA is affected?
speed of reading letters
what will the cover test look like with px with identity?
They will no manifest devation on cover, uncover . but may have latent on alternating cover test
What will the CT look like for a px without identity?
They will have a small manifest devaiton, less then 10 dioptres. They may appear to have a larger compenetn on alternating CT.
how do you assess sensory fusion?
bagolini lenses and worth’s lights
what is wrong with using worth’s lights > bagolini lenses?
WL is difficult to show suppression scotoma/central suppression
how do you assess motor fusion?
20^BO and PFR
what does motor fusion tell you about a heterophoria?
indicates how well compensated the hetereophoria is
is there stereoacuity in someone with microtropia?
reduced - RARELY stereoblind
what test is stereovision harder with?
random dot stereogram as they do not have bifoveal fixation
how do you assess fixation?
use ophthalmoscope/visuscope
- have px fix on centre of target
- cover px’s non-fixing eye
- comment on location of fixation as well as if the fixation is steady or wandering
what is normal retinal correspondence also knwon as?
bifoveal fixation
how does the 4^BO test workin px with bifoveal fixation (normal)?
- prism place in front of RE - image is displaced away from fovea RE adducts to maintain fixation
- LE moves (herrings law) as image to LE falls on temporal retina and projects nasally resulting in dip
- diplopia causes nasal movement of LE to maintain BSV
how does 4^BO work (in left microtropia)
- prism placed in front of RE - image is displaced away from fovea RE adducts to maintain fixation
- left eye moves out (herrings law), image to the LE now falls within the supression scotoma resulting in NO diplopia response
- prism placed in front of LE, image falls within the suppression scotoma so there is NO movement of EE seen
what do you write down if you have carried out 4^BO test and they DONT have a microtropia?
4^: bifoveal fixation
what do you write down if you have carried out 4^BO test and they DO have a microtropia?
4^: +ve supression scotoma (L/R)
main management:
optimise VA
how do you optimise VA?
- cyclo
- glasses worn full time for full refractive period (16-22 weeks)
- part time total occlusion prescribed - cease once no further imporvement for VA
- continually monitor fixation/supression throughout treatment
what is the interocular difference often seen between the eyes?
0.1-0.3 logMAR
what 3 factors have a great baring on visual outcome?
- fixation
- degree of anisemotropia
- compliance
is there a difference between how you treat WITH and WITHOUT identity?
no
what do majority of microtropic px’s have?
anisemotropia
what does identity relate to?
fixation rather than cover test findings
When do you start occlusion therapy?
After 16-22 Weeks, if the vision has not improved. When occluding we will neeed to monitor their fixation and suppression throughout their treatment
When a young px has come in with anismetropia what do we do?
We will need to give them the correction then see them in 16-22 weeks - if visions still shit then refer for occlusion
what is the normal diffrence between eyes?
0.1 - 0.3
If the vision has not improved what is important to let the parents know?
The child will need to wear full time and probs will not grow out of them
what we treat after the age of 7?
Sometimes with anismetropia and microtropia we can sometimes treat them
