Investigation of Heterophoria Flashcards
What is co-morbidity?
The act of having an associated condition
What is heterophoria also known as?
Latent Strabismus
What is the difference between concomitant and incomitant heterophorias?
Concomitant :
- Angle of the deviation remains the same in all directions of gaze
- Angle of the deviation remains the same no matter which eye is fixing.
- Angle may vary over viewing distance
Incomitant :
- Angle of the deviation differs in different directions of gaze
- Angle is dependant on which eye is fixing.
What test do we use to determine whether a phoria is conocimtant or incomitant?
Ocular motility + Cover test
What would you do if a px came in with an incomitant phoria - recent onset?
REFER
True or False- a px can have a concomitant deviation that changes by viewing angle
True- a phoria is still concomitant if it changes at different viewing distances as long as the size of the deviation doesn’t change on versions
If the angle of a phoria doesn’t change on different viewing differences what do we term it?
“Non- specific”
How do we classfiy a phoria?
By deviation e.g. XOP or SOP
and then by seeing if the size of the deviation changes at different viewing distances.
If at a distance - ask your self what do eyes normally do at this distance - converge or diverge?
If deviation is in direction of movement that is meant to be made at that distance ( e.g. in the direction of convergence so moving inwards, or in the direction of divergence so moving outwards) the the phoria is in excess if not its in weakness.
E.g. SOP largest at distance would be termed a diverge weakness Esophoria.
e.g. XOP largest at near would be termed a: converge weakness exophoria
If a heterophoria is compensated is it likely to be symptomatic or asymptomatic?
Asymptomatic
What does a decompensated phoria mean?
It breaks down from being a phoria into a tropia.
Does a compensated phoria require treatment?
No
What happens to the power of the lens as we accommodate?
It becomes fatter and so more positve.
What different things can cause decompensation of a phoria?
Uncorrected refractive error :
imagine a child is a hyperope they will accommodate loads and then converge resulting in an esophoria to become an esotropia.
If they are myopic and uncorrected they wil diverge their eyes and not accommodate resulting in an exotropia.
Equally corrected refractive error can also cause decompensation.
Anisekonia (following anisometropia):
- especially after cataract surgery - as they do one eye at a time and leave the lens power as plano after so a px with a really high rx will have one realy high untreated eye and one plano eye.
Pathology:
- equally a cataract in one eye and not the other would mean the eyes can’t work together.
Other examples of pathology would be:
EOM abnormalities.
Accommodative anomalies
Reduced Fusional reserves
What other things can cause someone whos on the verge to decompensate?
Pregnancy - for the strain on your body that it is.
Poor general health
Trauma
Alcohol - because it is a muscle relaxant and so if your at the edge it will cause decompensation.
Drugs
Big lifestyle changes e.g. going from far sighted work to lots of near sighted work e.g. from being a plane spotter to a jeweller.
Occupations with a lot of Monocular work (e.g. microscope).
What symptoms associated with heterophoria are due to the effort it takes to maintain binocular single vision?
Headache
Eyestrain
Asthenopia
What symptoms associated with heterophoria are due to a failure in being able to maintain binocular single vision?
Diplopia
Blurred vision - when the diplopia is very small- when its side by side
Jumbling of letters
How do we investigate heterophoria in history and symptoms - what questions do we ask?
- History:
- Symptoms (Sx)
- When did they start
- How regular
- Are they progressing
- Do they become worse after any particular activity
- Can they be stopped
- General health - good or bad , medication
- POH (Any cataract surgery, strabismus surgery, changed Rx)
- Recently changed jobs?
- Any new lifestyle changes?
Why do we do a cover test with glasses on?
Cause of decompensation could be due to rx.
Equally the prescription we give could be being used to treat the phoria .
In a px with a heterophoria that is decompensating why is it important to check visual acuity?
Cause of decompensation could be change in rx and once corrected that could all be fine.
Equally to rule out that the decompensating is not due to pathology.
What test do we do to determine whether a deviation is compensated or not?
Cover Test - more specifically the recovery on the cover test.
If you find a phoria on cover test what is the next test you do and why?
Ocular motility to check for incomitancy
If you find incomitancy on a cover test what do you do?
Refer - unless it is congneital or the hospital are already monitoring/have monitored and discharged
Why do we test convergence in px with a heterophoria?
Sometimes a convergence problem co-exists with a heterophoria.
How do we test convergence?
Using an RAF rule
3 TIMES
Once subjectively - asking them to tell you when the line is double
Once objectively - watching both their eyes to see if they both converge - if not note which eye diverges
Why do we test accommodation in px with heterophorias?
Sometimes accommodation problem co-exists with heterophoria
What are the three ways in which we measure accommodation?
Using an RAF rule - measure 3 times monocularly and binocularly.
Accommodation facility - using flippers and seeing how many cycles they can complete in a minute
Dynamic ret - so target at your working distance with their prescription on and seeing if there is with or against movement there
What deviations do we test mallet unit on?
Only latent phorias.
What is ‘slip’ in a fixation disparity test?
The red and blue lines not being aligned on top of eachother in the centre above and below the cross.
What are the two schools of thought on when to treat a heterophoria?
Some people use the mallet unit test - and so say if there is slip and the px is also experiencing symptoms then treat. & if there is slip but the px isn’t experiencing symptoms then don’t treat.
Generally in optometry we follow the:
If a pre-presbyope - px must have slip greater than one dioptre + be symptomatic for us to treat.
For a prebyope - px must have slip greater than 2 dioptres and be symptomatic for us to bother treating.
What does it mean to have crossed diplopia?
Fake double image appears on the side of the physiological eye.
What does it mean to have uncrossed diplopia?
Fake image appears on side of pathological eye
If an image hits nasal retina where is it projected?
Temporally
If an image hits temporal retina where is it projected?
Nasal Retina
How can you use prism fusion range to tell whether a phoria is well controlled or not?
- reduced fusional range means poor control.
What are the benefits of using prism fusion range over a cover test (recovery) to assess how well a phoria is controlled?
PFR - allows quantifiable data - which can be used for monitoring purposes.
- allows you to compare to normal values
What are the normal values for Prism Fusion Range?
At Near: 35-40 BaseOut 15-20 BaseIn
At Distance: 15-20 BaseOut 5-10 BaseIn
(way to remember it is that the numbers double)
For vertical it is 3 base Up and 3 base down
For intorsion it is 3 degrees cyclo and 3 degrees incylo
What is Herring’s law of innervation and does it apply monocularly or binocularly?
Equal innervation between both eyes - e.g. if right eye moves to the right so will left.
Binocularly
Does sheringtons law apply monocularly or binocularly?
Monocularly
True or False- the more prism the px can overcome the more likely they are to break down
False
When do we use the 20 dioptre base out test?
When short of time
For younf children who can’t do Prism fusion range
As a screening test
If you were short of time and wanted to test the phoria how would you go about doing it?
So if their eyes are e.g. exo you want to test how much more their eyes can move out - thus using a base out.
If eso you would want to test how much more their eyes can move in thus using base in.
To Test we use base diorection that is same as the deviation
How do we test a hyper deviation?
We put a base up in front of the higher eye
Technically how would we test a hypo- deviation?
we put a base down infront of the lower eye
How do you measure the extent of the deviation using prism cover test?
Essentially you measure how much base prism in the opposite direction of the deviation is needed to make the eyes straight.
To measure you have the base direction in the opposite direction to the deviation
e.g. to measure exo you ave base in, to measure eso you would have base out
What different tests can we use to measure stereoacuity?
¡Lang I & II (No glasses)
¡Titmus
¡Frisby (No glasses)
¡TNO
¡Synoptaphore
¡Lang 2 pen
What are the advantages of using the prism cover test to measure deviation?
It is the most dissociative test and so gives you the largest most accurate result.
Why do we work out the accommodative ratio?
Gives us an indication as to how to manage the patient
What does an accommodative ratio of 1:8 mean?
For every one dioptre of accommodation the eyes move in by 8
What lenses cause accommodation?
Negative lenses force accommodation
What power lenses could you prescribe for a px who has a 16 prism exo deviation and an accommodative ratio of 8:1?
-2 lenses because 16/8 equals 2.
How do we calculate accommodative ratio?
What does controlled bincoular acuity assess and how do we do it?
assesses control of phoria:
¡Measures level of visual acuity whilst BSV maintained
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¡Ask patients to read down letter chart whilst occluding one eye intermittently per line.
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¡Note when deviation becomes manifest (looses BSV) and tropia noticed on cover test.
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¡Note when patient can no longer read because they report diplopia (looses BSV).
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Carry out near and distance with and without Rx
How would we refract someone with a large phoria?
via a cycloplegic refraction - this is always necessary in children
