Heterophoria investigation Flashcards
what is the meaning of co-morbility when considering the cause of the heterophoria
if the heterophoria may be caused by another eye condition and if you want to treat that eye condition first which can cause a decompensating heterophoria to disappear
what 2 things do you want to consider when deciding on your management
- Further monitoring/immediate treatment?
i.e. isit bad enough to treat now or you can just manage it more closely - What type of treatment?
is most appropriate for a particular case of heterophoria
what is heterophoria also known as
latent strabismus
what occurs in someone with a heterophoria when both of their eyes are uncovered
the visual axes are directed towards the fixation target
what occurs in someone with a heterophoria when the eyes are dissociated (i.e. one eye is covered)
the eye behind the occluder deviates in a different direction away from the fixation point
what occurs in someone with a orthophoria when both of their eyes are uncovered
the visual axes are directed towards the fixation target
what occurs in someone with a orthophoria when the eyes are dissociated (i.e. one eye is covered)
the visual axes are still directed towards the fixation target
what are the 2 types of heterophoria
- concomitant
or - incomitant
what is a concomitant heterophoria
- 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
what is a incomitant heterophoria
- Angle of the deviation differs in different directions of gaze
- Angle is dependant on which eye is fixing
how do you decide if a heterophoria is concomitant or incomitant
by doing a ocular motility test
what will you do if there is a recent onset of incomitant heterophoria discovered by a ocular motility test and why
refer the px to the eye hospital as it could be a nerve palsy or pathology
what are the 3 classifications of a concomitant strabismus exophoria
- Divergence excess
- Convergence weakness
- Non-specific
what is a divergence excess exophoria
when the exophoria is greater at distance than at near
what is a convergence weakness exophoria
when the exophoria is greater at near than at distance
what is a non-specific exophoria
when the exophoria is equal at distance and at near
what are the 3 classifications of a concomitant strabismus esophoria
- Divergence weakness
- Convergence excess
- Non-specific
what is a divergence weakness esophoria
when the esophoria is greater at distance than at near
what is a convergence excess esophoria
when the esophoria is greater at near than at distance
what is a non specific-esophoria
when the esophoria is equal at distance and at near
list the 6 types of heterophoria
- SOP
- XOP
- L HyperP
- R HyperP
- IncycloP
- ExcycloP
when is a patient with a heterophoria usually symptomatic
when it is decompensating
compensating patients dont usually get symptoms
list 6 causes of decompensation
- optical
- secondary to pathology
- accommodative anomalies
- reduced fusional reserves
- medical causes
- other causes
list 4 optical causes of decompensation
- Uncorrected, incorrect or ill corrected refractive error
- Esophoria caused by uncorrected hypermetropic refractive error
- Exophoria caused by uncorrected myopic refractive error
- Anisekonia caused by cataract surgery
how does cataract surgery cause anisekonia (different retinal images)
because it is done one eye at a time, and if both eyes are - 7.00D then this causes a anisometropic rx as after surgery one eye will be emmetropic and the other still -7.00D will cause a huge anisekonia , causing the px to decompensate
what 2 things can decompensation caused by being secondary to pathology affect
- vision
or - EOMs
e.g. an AMD px as they can’t see out of one eye
list 5 medical causes of decompensation
- Poor general health
- Trauma
- Medication
- Alcohol
- Pregnancy
how do drugs and/or alcohol cause decompensation
if a drug has a muscle relaxing property to it
alcohol always has a huge muscle relaxant effect on the body
how does pregnancy cause decompensation
it causes increased stress on the body
list 4 other causes of decompensation
- Excessive VDU work
- Increase close work
- Increase distance work
- Occupations with a lot of Monocular work (e.g. microscope)
what 2 things are the symptoms associated with heterophoria due to
- Due to effort to maintain binocular single vision (BSV) = px trying to hold eyes together
- Due to a failure to maintain binocular single vision (BSV) = px could no longer hold eyes together
what 3 symptoms occur with heterophoria as a result due to effort to maintain binocular single vision (BSV)
- Headache
- Eyestrain
- Asthenopia
what 3 symptoms occur with heterophoria as a result due to a failure to maintain binocular single vision (BSV)
- Diplopia
- Blurred vision: where letters are just pulling apart
- Jumbling of letters
in which 13 ways can you investigate and manage a heterophoria
- history
- visual acuity
- cover test
- ocular motility examination
- convergence
- accommodation
- mallet unit/fixation disparity
- prism fusion range
- stereo acuity
- prism cover test - measure angle of deviation
- AC/A ratio
- controlled binocular acuity test
- refraction and fundus examination
list 4 things you will want to ask a px in history when investigating heterophoria
- symptoms
- general health: good/bad/medication
- previous ocular history (POH): cataract surgery/strabismus surgery/change in rx
- recently changed jobs: may be doing a lot of monocular work
list 5 questions you will ask a patient if they are having symptoms associated with heterophoria and what is the reason for asking these questions
- When did they start
- How regular
- Are they progressing
- Do they become worse after any particular activity
- Can they be stopped
as trying to see how bad the problem is i.e is it decompensating? and is it progressing? and what might be the possible cause
what does a patient who says their heterophoric symptoms can be stopped by covering one eye tell you
that the problem is binocular
what 2 things can investigating visual acuity when investigating heterophoria reveal/what 2 reasons will you check visual acuity and how should you do this
- it could be a sign of pathology: which usually happens to one eye and this explains why its decompensating
- it could be down to uncorrected/incorrect spectacles
- check va’s with new and old refractive correction
for what reason will you do a cover test when investigating heterophoria and how will you do this
- To diagnose the condition and determine whether it is compensated and know whether it is a divergence excess or convergence weakness etc
- Far distance (if deviation increasing)
- Remember to NOTE THE RECOVERY
for what reason will you do a ocular motility examination when investigating heterophoria and what can it reveal
- To ensure no incomitancy (sometimes a muscle weakness co-exists) and therefore know if you need to refer
Can reveal:
- Cyclophoria
- Vertical phoria
- SOP divergence weakness (L-R)
what can be done if a ocular motility examination reveals no incomitancy and therefore no muscle weakness
we can manage the patient’s decompensating heterophoria ourselves
which 2 problems can co-exist with heterophoria
- convergence problems
- accommodation problems
which test will you use to test for convergence problems which can be associated with heterophoria and how is it done
- RAF rule
- test it 3 times
- note which eye diverges (objective)
- Note whether diplopia noticed (subjective)
do it both objectively and subjectively
which tests will you use to test for accommodation problems which can be associated with heterophoria and how is it done
- Near point (RAF rule)
Measure monocularly and binocularly
Measure three times - Facility (with flipper lenses)
Use +/- 2.00D lenses - Dynamic ret
MEM or NOTT method
which type of patients is the Mallett unit usually carried out on
latent phorias (never tropias)
with which type of patient does an aligning prism (slip) CO-EXIST with in the mallett unit and what do you do for these patients
- px with a compensating heterophoria
- if no symptoms then no treatment is given
what is an aligning prism (slip) a sign of in the mallett unit and when will you decide to treat these patients
- sign of stress on the binocular system
- you only treat if they have symptoms present
where will the nonius lines/monocular image be perceived in fixation disparity with a patient who has a exophoria and what prisms will be given to these patients
- image perceived nasally
= crossed disparity - base in prisms
Nonius strips project onto temporal retina therefore image is perceived nasally
where will the nonius lines/monocular image be perceived in fixation disparity with a patient who has a esophoria and what prisms will be given to these patients
- image perceived temporally
= uncrossed disparity - base out prisms
Nonius strips project onto nasal retina therefore image is perceived temporally
which test is used to assess motor fusion
prism fusion range
what is prism fusion range used to assess in someones motor fusion
the control of their deviation
what does a reduced fusion range mean
poor control of their deviation or BV i.e. px more likely to decompensate with their phoria
what can you do with prism fusion range over time
Can monitor the progression over time (is the patient improving or deteriorating)
especially of you are treating the patient, you want to see if the treatment is working/starting to recover
which way is the apex of a prism directed in prism fusion range
it acts as an arrow and therefore points in the direction that the eye will move in
if a base out prism is put infront of the right eye, how will a patient who can compensate merge the image and overcome the diplopia
they will move their right eye in towards their nose to overcome the diplopia, therefore the left eye will also move to the left (herrings law) however it must move back in towards the nose to keep the image as one
what will a patient who decompensates experience with prism fusion range
px will not be able to pull eye back in once prism is placed infront of eye therefore will experience double vision as they cannot merge the image by themselves
which type of fusional reserve does a base out prism measure
positive fusional reserves = convergence
which type of fusional reserve does a base in prism measure
negative fusional reserves = divergence
which target must a px look at when measuring their prism fusion range
6/60
what is the order of which you should measure prism fusion range
Base in / base out / base up / base down
which value should you record your prism fusion range
one before the break point
which directions and distances should prism fusion range be measured
- vertical and horiszontal
- near and distance
when will you use the 20 base out prism test to check motor fusion
- with children too young to do PFR
- Place in front of either eye
what are the normal horizontal fusion ranges at distance
- 5-10 BI
- 15-20 BO
what are the normal horizontal fusion ranges at near
- 15-20 BI
- 35-40 BO
what are the normal vertical fusion ranges
- 3 BU
- 3 BD
what are the normal torsional fusion ranges
- 3 degrees excyclo
- 3 degrees incyclo
which fusional reserves are reduced in an EXO px (who has problems converging their eyes)
base out reserves reduced
which fusional reserves are reduced in an ESO px (who has problems diverging their eyes)
base in reserves reduced
which fusional reserves are reduced in an Hyper px
base up reserves reduced (IN FRONT OF HYPER EYE)
which fusional reserves are reduced in an Hypo px
base down reserves reduced (IN FRONT OF HYPO EYE)
which prism fusion range is the most important to measure
exo deviation (patients who have problems converging their eyes)
how must a prism be used when exercising someones prism fusion range
prism base always to be in the SAME direction as the DEVIATION
list 6 stereo tests that can be used to measure the control of deviation
- Lang I & II
- Titmus
- Frisby
- TNO
- Synoptaphore
- Lang 2 pen
what does measuring the angle of someones deviation allow you to do
monitor their progression which is very important
which is the best test to do when wanting to measure the angle of deviation and why
prism cover test
as it gives the greatest level of dissociation
which three things can the prism cover test do
- measure angle of deviation
- correct the angle of deviation
- neutralise the angle of deviation
how is the prism placed in prism cover test and list them for ESO, EXO, HYPER and HYPO
prism BASE always placed OPPOSITE to the DEVIATION
- ESO = Base out
- EXO = Base in
- HYPER = Base down (IN FRONT OF HYPER EYE)
- HYPO = Base up (IN FRONT OF HYPO EYE)
what will be the prismatic correction for someone who has a right esotropia
- base OUT prism (as it moves the image towards the apex)
Fixation target stimulates fovea of the LE & Nasal retina RE
Nasal Retina projects temporally
Uncrossed diplopia
name 2 advantages of the prism cover test
- Maximum dissociation (gives the maximum angle)
- Most accurate measurement
list 4 disadvantages of the prism cover test
- High level of concentration from patient
- Most difficult to carry out
- Cannot measure torsion
- Cannot be blind in one eye
what is the AC/A ration a measure of
accommodative convergence to accommodation
what do you need to do in order to determine the values for the AC/A ratio
do a prism cover test at distance and at near
why is an AC/A ratio of a patient worked out
In order to determine how to manage patient
list how the heterophoria method of AC/A ratio is worked out
- IPD (inter pupillary distance) measured in centimetres
- Wear refractive correction
- Deviation measure by PCT at near 1/3m (n) and distance 6m (d)
- D = amount of accommodation exerted = 3 Dioptres sphere
AC/A = IPD(cm) + n-d/D
e.g.
PCT near 20 BI distance 5BI =
6 + -20 - (-5)/3
AC/A = 1:1
which base direction is a negative value when calculating the AC/A ratio
Base IN with PCT
as your measuring someones exophoria
what is a normal value of AC/A ratio
3-5:1
what can you give a patient who has high AC/A ratio values as treatment
give them -ve lenses to make them accommodate more
as they’re not accommodating enough
which test assesses the control of a phoria
controlled binocular acuity
how does the controlled binocular acuity test assess the control of a phoria
it measures level of visual acuity whilst BSV maintained
list the steps of how you will do a controlled binocular acuity test in order to assess the control of a phoria
Ask patients to read down letter chart whilst occluding one eye intermittently per line. (to see where they decompensate)
Note when deviation becomes manifest (looses BSV) and tropia noticed on cover test.
Note when patient can no longer read because they report diplopia (looses BSV).
Carry out near and distance with and without Rx
how can you assess the control of a phoria with the controlled binocular acuity test in a patient who is suppressing or does not notice when they get diplopia
whilst doing the cover test you will notice if they decompensate when their straight eye becomes strabismic
e.g. if half way down the chart the px becomes a left ESOT, as you cover the other/right eye, the left eye has to move out.
if the px was straight, then the eyes won’t move
why must you carry out a refraction and what type of refraction must you do when assessing someones heterophoria
- a cyclopegic refraction (always necessary in children)
- to see what effect does correction have on the deviation
why must you carry out a fundus examination when assessing heterophoria
to ensure nil pathology
