measurement of heterophoria and heterotropia Flashcards
what is important to assess during every sight test and why
the oculomotor balance of your patient to look for common binocular vision problems
as this can affect the way in which you do your refraction and/or the way you manage your patient
how is a heterotropia viewed under normal viewing conditions
one eye does not fixate on the object of regard - it either turns in or out or up or down, in relation to the other eye
when do people usually develop a tropia and what can this cause as a result
during childhood, therefore a patient tends to adapt to the deviation of one eye by suppressing the image, thus preventing diplopia
when may a patient report diplopia in relation to their tropia
if they develop a tropia later in life e.g. due to a stroke that can damage one of the nerves supplying a particular EOM
then the px is very likely to report diplopia
what will a patient who has a tropia, most definitely not have
binocular vision i.e they cannot fixate on an object with both eyes at the same time in certain conditions
under what type of conditions may a px with a tropia to achieve binocularity
some patients are able to view binocularly at distance but not at near, or when wearing glasses but not without
what is a advantage to people who have an alternating tropia
they should have reasonably good vision in both eyes as both eyes have been used during visual development
what three things is a tropia described in terms of
- the size of the angle: estimated during cover test of prism bar
- the direction of the deviation
- the eye that deviates
e. g. 10 ^ right esotropia (the right eye turns in by 10^)
how is a cover test carried out on a px with a tropia
- the deviating eye is covered while the practitioner studies the fixating eye, watching for any movement - there should be none as fixation has not been disrupted
- the cover is then removed in a sharp movement while watching for movement of the eye that was covered - there should be none
- the fixing eye is then covered and the angle through which the deviating eye turns to take up fixation is estimated
- this angle is known as the angle of the squint
- the eye under the cover will also move through the same angle and a refutation movement occurs following removal of the cover
what is 1mm of movement equivalent to in prim
2^
what can be used to measure the size of the deviation in a px with a tropia
a prims bar, placed over the deviating eye and the power gradually increased until no movement is seen on cover testing
what does a phoria mean
that the natural, relaxed position of the eyes is not the same as the position of the eyes when they are fixating an object, whether it be parallel visual axes when viewing a distant object, or convergent visual axes when fixating at near
what happens to heterophoric eyes when they are dissociated i.e. prevented from both viewing the fixation target by the distortion of the image or the covering of an eye
the dissociated eye will move to take up its heterophoric position which may be in or out or even up or down in relation to the other eye
when the dissociation is removed, the eye returns to fixate normally
does it matter which eye you dissociate with a phoria
no, the heterophoric angle between the two eyes will remain the same
what 2 things is a heterophoria described in terms of
- the angle of deviation (on dissociation)
- the direction of deviation
e.g. 4^ exophoria
(no need to state the eye as its the same amount, whichever eye is covered)
what do both hetertropias and heterophorias vary in size with and thus what is important to do
both vary in size with different fixation differences
therefore should be assessed for distance and near maybe intermediate if px is a VDU user
also assess the oculomotor status of the visual system corrected and uncorrected
when will you decide to maybe not assess someones oculomotor status of the visual system corrected and uncorrected
if they have a significantly large refractive error and is consequently likely to be wearing their contact lenses or glasses constantly
what are the four ways of dissociating someone with a free and state which test is used for each way of dissociation
- prevent both eyes from viewing the fixation object by covering one eye: the cover test
- distortion of one retinal image: the maddox rod
- viewing two separate objects: maddox wing and polaroid tests
- prism dissociation
what are the advantages of doing a cover test
- quick and simple
- requires only a occluder
- can be undertaken in a variety of viewing distances
- allows you to look at the speed of refixation (recovery), which tells you how well the phoria is controlled and how likely it is to cause a patient problems
list the four things that should be stated in your cover test results
- is it a phoria or tropia
- direction of deviation: exo, eso, hyper, hypo or combination of horizontal and vertical elements
- magnitude: in prism diptres ^
- recovery speed of bifocal fixation in heterophoria
what can be used to obtain the size of the movement of a phoria/tropia
by neutralising any movement by putting lose plano prisms in the trial frame, or using prism bars
the prism should be held over one eye during cover test and the amount of prism increased until no movement in seen on cover test
what is the smallest possible movement you can see in a cover test
2^
in which circumstance must you refer to the eye along with the direction of the deviation when classifying a heterophoria
with vertical heterophorias
how must vertical heterphorias be recorded
if the covering of one eye results in supraduction (upwards) then the other eye will definitely infraduct (downwards) when covered
therefore a right hyperphoria is identical to a lest hypophoria and vice versa
when recording your findings, it is always the recorded at the higher eye (supraduction) e.g. as a right or left hyperphoria
what type of phoria can not be controlled with prisms
cyclophoria
what is required is a cyclophoria is symptomatic and why
surgical intervention as they cannot be corrected with prisms
what can a cyclophoria arise from
following trauma
how can a movement from cyclophoria be detected in a cover test
it can only be detected if the patient has some form of reference mark on their eye such as a iris naevus
what may a patient with a cyclophoria report about the streak on the maddox rod
the streak is oriented obliquely
which two tests can be used to measure/detect a cyclophoria
- maddox rod
- maddox wing
what are the two reasons to carry out an alternating cover test
- to amplify the movement you may see
- use subjectively where you are unsure of a movement. the patient can often appreciate a movement subjectively that is invisible objectively
what phoria corresponds to if the movement of the image is in the same direction as that of the cover
exophoria
what phoria corresponds to if the movement of the image is the opposite direction as that of the cover
esophoria
