lecture 6 - measurement of ocular deviation Flashcards
why should you measure ocular deviation?
- enables us to diagnose
- ensures consistency between examiners
- find max deviation therefore can decide when to manage/monitor
- monitor progression
- relate size to fusion range or other clinical features
- to calculate AC/A ratio
how do you measure ocular deviations using the objective prism cover test
- carry out normal cover test
- place prism of estimated strength in front of deviated eye (either if phobia)
- apex always in direction of deviation
- carry out alternating cover test SLOWLY
- look at eye behind the prism bar
- increase prism strength until opposite movement then record results as the prism seen before reversal
how do you measure ocular deviations using the Hirschberg test
px fixates on pen torch at 33 cm
corneal reflections noted in foxing été and compared to other eye
displacement estimated
how do you measure ocular deviations using the krimsky test
Patient fixes on light at 33cm
Corneal reflection noted in both eyes
Estimated prism placed in front of fixing eye
Strength increased until the corneal reflexes in deviated eye equal to position in fixing eye initially
Can be used with prism before deviating eye (prism reflection test)
how do you measure ocular deviations using the subjective prism cover test
- Head straight- target same size as before - Carry out Cover Test
- Place prism of estimated strength before deviated eye or either if phoria
- Carry out alternating cover test
- Ask the patient if they notice image moving from side to side or Up to down
- Find prism strength to neutralise movement of images as cover is moved from one eye to the other
- Make deviation reverse then record prism before reversal
how do you measure ocular deviations using the Maddox rod
high powered cyls make the spot of light turn into a streak perpendicular to the direction of the grooves
other eye views the spot light
placed before either eye in latent
conducted in darkened room
increase prism until spot and image coincident
prism is equal to angle of deviation
how do you measure ocular deviations using the Maddox wing?
- held in reading position
- allow px time to dissociate
- px asked what number the white and red arrow point to
does prism cover test measure latent or manifest deviations?
both - it gives you the total deviation
disadvantages of prism cover test
only as reliable as the clinician
requires px co-operation
which accommodative target do you use for prism cover test?
line above weakest VA
spot light if less than 6/60
how does the prismatic correction in the PCT work? eg. using RSOT
fixation target stimulates fovea of LE and nasal retina of RE - which projects temporally resulting in uncrossed diplopia
place base out in front of RE to alleviate diplopia, as the base out prism will move the image towards the apex, bringing it back into the centre
advantages of PCT
accurate measurement
measures full angle
disadvantages of PCT
dependant on ability to fixate accurately
cannot measure cyclodeviations
unreliable with poor VA
cant be used in young children
when would you use simultaneous prism cover test?
when your px has a manifest strabismus with a latent component
what does SPCT measure?
manifest deviation only
how do you carry out SPCT?
Perform cover test to determine type & estimate angle of deviation
Prism of estimated strength placed before deviated eye while occluder simultaneously covers fixing eye (cover/uncover cover test)
Keep increasing strength until neutral movement achieved
how do you carry out SPCT?
Perform cover test to determine type & estimate angle of deviation
Prism of estimated strength placed before deviated eye while occluder simultaneously covers fixing eye (cover/uncover cover test)
Keep increasing strength until neutral movement achieved
if red reflex is brighter in one that then the other what does this indicate?
they could have cataract, corneal abrasion, foreign body or strabismus
what is the Bruckner test?
screening test that allows you to detect manifest deviation
1mm displacement of corneal reflectionis approx how many degrees?
12
1mm displacement of corneal reflection is how many prism dioptres?
20-22
when do you use the krimsky test?
when you have manifest deviation and fairly poor vision in one eye
when do you use the prism reflection test
when you have manifest deviation and fairly good vision in both eyes
how do you do the prism reflection test?
base in opposite direction, put in front of manifest eye, increase bar strength until corneal reflection in the same in both eyes
advantages of using corneal reflections?
prism reflection test is good for uncooperative px’s
krismky is good for blind or one eye with very poor vision
disadvantages of using corneal reflections
cant measure latent deviations
will not detect microtropias
accommodation is not controlled
why is subjective PCT useful?
Useful in small symptom producing vertical deviation
if the image appears to move side to side WITH the occluder when carrying out subjective PCT…
exophoria
if the image appears to move side to side WITHOUT the occluder when carrying out subjective PCT…
esophoria
advantage of Maddox Rod
relatively easy to use
detects and measures torsion in cyclodeviation
disadvantage of Maddox rod
accommodation not controlled
can’t have suppression or ARCC
slight head tilt may stimulate vertical deviation
nears fairly good VA in either eye
disadvantage of Maddox rod
accommodation not controlled
can’t have suppression or ARCC
slight head tilt may stimulate vertical deviation
nears fairly good VA in either eye
if Maddox Rod is places before the right eye where will the red bar be in relation to the spot light - esodeviation
to the right (uncrossed)
if Maddox Rod is places before the right eye where will the red bar be in relation to the spot light - exodeviation
to the left (crossed)
how to test cyclodeviations using the Maddox rod
px reports if tilted or torsion is syspected
- 2 vertical Maddox rods are inserted into trial frame
- if separation between lines use a vertical prism
- px or practitioner rotates rods so that they appear straight and parallel
- amount of cyclodeviation is measured on trial frame in degrees
- used for distance and near viewing in primary position
if a patient reports even numbers when using Maddox wing, what does this suggest?
they have an exodeviation
if a px reports odd numbers when using Maddox wing, what does this suggest?
they have an esodeviation
how is torsion indicated when using the Maddox wing?
if the red horizontal arrow is not parallel with the grading scale
in this case the px is asked to adjust arrow themselves until it is parallel
advantages of Maddox wing
easiest
quickest
measures latent horizontal, vertical and cyclodeviations
disadvantages of Maddox wing
- near only
- set distance of 33 cm
- accommodation effects results PD fixed
- can’t have suppression or ARC
- unreliable in the presence of poor VA
- not good with uncooperative px’s
- septa bend easily not fully preventing peripheral fusion
should these tests be carries out with correction?
All tests SHOULD be carried with and without correction if it influences their deviation
when do spectacles not impact the deviation?
when you are presbyopic
what target do you use for prism fusion range if:
R - 6/9
L - 6/5
6/60 - you always choose 6/60 when they can see it, if not it is the spotlight
which tests can measure torsional components?
Maddox wing and rod
how would you explain what a PCT measures to a px? (esophoria)
“your eyes are slightly turned in towards your nose, so i’m going to measure how much it is turned in by”
how would you explain what a PCT measures to a px? (exophoria)
“your eyes are straight but when i cover one eye at a time, they have a tendency to move out a little bit so i’m going to measure how much it is”
