Cover Test Flashcards
A cover test is used to determine:
- presence of a 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
What is orthophoria?
The perfect alignment in the absence of a stimulus for fixation
Define Heterophoria/phoria
The tendency for the eyes to deviate when fusion is blocked
A small ___ is common in most people; overcome by fusion
phoria
A “posture” slightly inward is _____
esophoria
A “posture” slightly outward is ____
exophoria
When motor fusion is no longer enough to overcome a phoria, it is called a _________ phoria.
decompensating
A decompensating phoria could result in
discomfort or diplopia
-double VA may occur
Hetertropia/Tropia is a _____ deviation
manifest
_______ is when the visual axes of both eyes do not intersect at fixation.
Eye is NOT aligned properly
Heterotropia/Tropia
Heterotropia/Tropia leads to
diplopia or suppression of the deviated eye
A tropia could occur due to some of the following reasons:
- Ansiometropia (difference in refractive errors between the two eyes)
- Abnormality of the extraocular muscles or strabismus
- Eye disease
Cover-Uncover Test (Unilateral Cover Test): Helps to differentiate:
- presence of a deviation (phoria/tropia)
- laterality/which eye (unilateral or alternating)
- frequency of the deviation (constant/intermittent)
The cover-uncover test is done _____
first!
Alternating cover test determines the:
- direction of the phoria/tropia
- magnitude (size) of the deviation
Both Cover-Uncover (Unilateral Cover Test) and Alternating Cover Tests are performed at
distance AND near
What does the “cover” show in the Cover-Uncover Test?
If the deviation is a phoria or a tropia
presence
___ in Cover-Uncover evaluates the visual axis of each eye when both eyes are viewing a target.
“Cover”
In the Cover-Uncover test, which eye do you look at?
The eye that is NOT covered
In a Cover-Uncover Test:
____ is where the visual axis of both eyes are aligned on the target with both eyes open
Phoria
In a Cover-Uncover Test:
___ is where the visual axis of one eye is aligned on the target while the other is misaligned with both eyes open. It will have to move to pick up fixation.
Tropia
“Uncover” in a Cover-Uncover Test shows
- if a tropia is alternating or unilateral tropias (Lateralitly)
- if a tropia is constant or intermittent (frequency)
For “Uncover” in a Cover-Uncover Test, you focus on the eye
that is NOT occluded to determine if it picks up fixation.
“Uncover” in Cover-Uncover Test:
A(n) _____ tropia is when one eye usually fixates when both eyes are open.
unilateral (right or left)
For a unilateral (right or left) tropia, the tropic eye
only fixates when the preferred fixating eye is occluded
A(n) _______ tropia is when the patient is able to keep either eye (visual axis) on a target with both eyes open.
alternating
Equipment needed for Cover Tests: (6 things)
1) Visual Acuity Chart for Fixation at distance
2) Near Point Target for Fixation at near
3) Occluder/paddle
4) Horizontal and vertical prism bars or loose prisms
5) Habitual Correction (CT will be done with and without correction in some cases)
6) Well lit room
How do you explain the purpose of the Cover Test(s) to your patient?
“I want to make sure your eyes are aligned properly.”
For a cover test at distance,
isolate a letter that is 1-2 lines larger than the best corrected visual acuity (BCVA) in the poorer seeing eye.
For a cover test at near,
hold an accommodative target at 40 cm (16 inches)
What can you do for kids when doing a cover-test at near?
Put the accommodative target on your nose
The accommodative target for the near cover-uncover test should be
comparable detail/size (20/30 size)
If there was any movement on unilateral cover test, the patient has a
tropia
If you saw movement on a unilateral cover test, you must determine if the tropia is unilateral or alternating by
observing the movement of the uncovered eye
What prism do you use to neutralize an exo (eye out) deviation?
Base In (BI)
What prism do you use to neutralize an eso (eye in) deviation?
Base Out (BO)
What prism do you use to neutralize a Hypo (eye down) deviation?
Base Up (BU)
What prism do you use to neutralize a Hyper (eye up) deviation?
Base Down (BD)
What prism do you use to neutralize an ortho (alignment)?
Verify ortho by using BI and then BD
To assess fixation in a cover-uncover test,
determine if the patient is able to fixate with the right eye when the left eye is coverd, and then evaluate if the left eye is able to fixate when the right eye is covered.
Observe any movement of the right eye as soon as the left eye is covered. If there is no movement, that means
the right eye was fixating when both eyes are open
Steps to Measure the Deviation:
- Put prism in front of eye and watch the other
- Continue to move the occluder back and forth while increasing the 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
