Cover test Flashcards
Cover test is done to determine…
- presence of deviation (phoria or tropia)
- laterality/which eye (unilateral or alternating)
- frequency of the deviation (constant or intermittent)
- direction of the phoria or tropia
- magnitude (size) of the deviation
orthophoria
the perfect alignemtn in the absence of a stimulus for fixation
heterophoria/phoria
the tendency for the eyes to deviate when fusion is blocked
-a small phoria is common in most people; overcome by fusion
phoria with “posture” slightly inward
esophoria
phoria with “posture” slightly outward
exophoria
decompensating phoria
when motor function is no longer enough to overcome a phoria. discomfort or diplopia
heterotropia/tropia
- manifest deviation
- visual axes of both eyes do not intersect at fixation
- leads to diplopia or suppression of the deviated eye
reasons for tropia
- aniosmetropia
- abnormality of the extraocular muscles or strabismus
- eye disease
anisometropia
difference in refractive errors between the two eyes
cover-uncover test (unilateral cover test)
- presence of deviation (phoria or tropia)
- laterality/which eye (unliateral or alternating)
- frequency of the deviation (constant or intermittent)
- this test done FIRST
Which test should be done first?
cover-uncover test
-want to make sure you don’t break fusion
alternating cover test
determines:
- direction of phoria or tropia
- magnitude (aize) of the deviation
At what distance is the cover test done?
at distance and near
“Cover” in the cover-uncover
- show if deviation is phoria or tropia
- evaluates the visual axis of each eye when both eyes are viewing a target
- look at eye that is NOT covered
phoria
the visual axis of both eyes are aligned on the target with both eyes open
tropia
the visual axis of both eyes is aligned on the target while the other is misaligned with both eyes open. Now it has to move to pick up fixation
“uncover” in cover test
- shows if a tropia is alternating or unilateral (laterality)
- shoes if a tropia is constant or intermittent (frequency)
unilateral tropia
R or L tropia is when one eye usually fixates when both eyes are open
-the tropic eye only fixates when the preferred fixating eye is occluding
alternating tropia
pt able to keep either eye on a target with both eyes open
equipment for cover test
- VA chart
- near point
- occluder/paddle
- prisms
- habitual correction
- well lit room
how do you explain purpose of cover test to patients?
“I want to make sure your eyes are aligned properly
How to do cover test
- sit or stand in a way that you can see the eys but does not block pts fixation. Hold occluder and prisms
- tell pt to look at target and keep it clear
- determine if pt is able to fixate with the right eye when the left eye is covered, and then evaluate if the left eye is able to fixate when the right eye is covered
- observe any movement as soon as the left eye is covered
- allow 2-3s for eyes to ressume relationship with each other
- repeat a few times
- repaet with other eye
How to do cover test at distance
-at distance, isolate letter that is 1 or 2 lines larger than the best corrected VA in the poorer seeing eye
How to do a cover test at near
- hold target at 40cm
- leter 1-2 lines larger than BCVA of poor eye
- target of comparable size. pt can hold target
What does it mean if there is no movement in the eye if the other is occluded?
eye was fixating when both eyes were open. if its the same in both eyes with no movement it is phoria
tropia
if there was any movement on unilateral cover test
How do you determine if the tropia is unilateral or alternating?
observe the movement of the uncovered eye
alternating cover test
determines the direction and the size of the deviation
how to do alternating cover test
- tell pt to look at target and keep it clear
- place occluder in front of right eye for 2-3 seconds to break binocular fusion
- quickly alternate and move the occluder to the left eye, observing right eye you just uncovered for directional movement
**watch uncovered eye for the refitting action and direction
measuring the deviation
- prism in front of one eye and watch the other
- keep moving occluder back and forth while increasing prism until you no longer see movement
- deviation is neutralized at the amount of prism where both eyes appear aligned and there is no more movement on alternate CT
Exo
BI prism
Eso
BO prism
Hypo
BU prism
Hyper
BD prism
Ortho
verify by using BI and then BO
recording tropia or phoria
- cc/sc
- distance and near findings separately. add prime (‘) for near results
- amount of prism used to neutralize
- direction of deviation
- phoria or tropia
- R/L for tropia
E
esotropia/esophoria
X
exotropia/exophoria
RH
Right hypertropia/hyperphoria
LH
left hypertropia/hyperphoria
record Ortho
for no deviation
when recording tropia
- L/R
- alt (alternating)
- intermittent tropia (T)
- amount of prism
Horizontal phorias
usually not recorded like this sine the phoria is a relationship between the two eyes
laterality
alternating
frequency
intermittent
magnitude
amount of prism
presence of deviation
phoria/tropia
CT cc 20PD RX(T) at N
Cover test with correction 20 prism diopters right intermittent exotropia at near
expected finding
about 0-3 XP at N
when recording…
mention presence, laterality, and frequency
comitancy
deviation size remains same (or within 5pd) in all positions of gaze
-implying no muscles are underacting or overacting
noncomitancy
deviation size changes in difference positions of gave
-due to an over action or under action of one of multiple muscles
to determine comitancy
CT is done in all positions of gaze
