Cover Test and related topics Flashcards
Cover Test: Procedure Cover Test: Interpretation of Results Local Sign Corresponding Points Strabismus Amblyopia (intro)
Where does the cover test get it’s name?
An occluder is used to COVER an eye
What is the purpose of the cover test?
To identify a “misalignment” of the eyes
Why is the cover test important?
Eye misalignment has the potential to lead to AMBLYOPIA in children
Where does fusion take place?
Neocortex in the central processing part of the fusional system
To have successful fusion, the brain has to interpret the info coming from the two eyes as coming from the same ________ AND ________.
visual target AND location
Retinal images and neural signals that the info (from the same visual target) causes must be ________ for fusion to be successful.
very simmilar
How does the brain “know” where something is located?
It interprets the object’s location according to the location of the object’s image on the retina, the “local sign.”
What is the Local Sign?
The location of the image of an object on the retina which allows the brain to interpret the location of the object.
When the retinal images in the two eyes have the same Local Sign, we say that the images are falling on ___________.
Corresponding Points
Target used for cover test has to have _____ visual detail.
fine
The cover tests are performed at distance, ___ ft, and at near, ___ cm.
20 ft and 40 cm
two parts of the cover test are…
- Unilateral or “Cover-Uncover Test”
2. Alternating Cover
First Law of the Unilateral Cover Test: An eye moves in order to _____, because it was not already ______.
fixate; fiaxting
Second Law of Cover Test: If an eye does not move, it was ________.
already fixating
When performing the Unilateral/Cover-Uncover Test, the eye that moves is said to have a _____.
tropia
When performing the Unilateral/Cover-Uncover Test, which eye do you look at/observe?
The eye that you are not covering; the other eye.
Unilateral Cover Test Procedure: 1. 2. 3. 4. 5. Repeat on OS
- Cover the OD first while observing the OS
- Keep the occluder on for 2-3 seconds
- Remove the occluder for 2-3 seconds
- Repeat to make sure your observations were accurate and are confirmed
- Repeat on OS
Interpretation of the Unilateral Cover Test:
Cover OD while observing OS
OS did NOT move
Conclusion: _____________
No tropia in OS
Interpretation of the Unilateral Cover Test:
Cover OD while observing OS
OS DID move
Conclusion: _____________
Tropia in OS
Interpretation of the Unilateral Cover Test:
Cover Os while observing OD
OD did NOT move
Conclusion: _____________
No tropia in OD
Interpretation of the Unilateral Cover Test:
Cover OS while observing OD
OD DID move
Conclusion: _____________
Tropia in OD
If a tropia is observed in both eyes during the Unilateral Cover Test, the patient has a/an _______.
Alternating tropia/strabismus
What is the goal of the unilateral cover test?
To detect the presence or absence of strabismus.
Define strabismus/tropia
Misalignment of an eye
Define diplopia
Double vision
Define amblyopia
Reduced vision not due to refractive error or pathology
Two common causes of amblyopia are ______ and ____.
- strabismus/tropia
2. anisometropia
A constant strabismus will result in either _____ or _____.
diplopia or suppression
When suppression is prolonged, it becomes _____ and the VA in that eye is _____.
permanent and reduced
Define bifixation
Each eye is fixating (looking at) the same target
The alternating cover tests allows to check for _____.
phoria
Define phoria
Misalignment of the eyes that is present ONLY when fusion is broken.
Define “phoria position”
Position the eyes go to when fusion is broken
At the beginning of the alternating cover test, where do you have the occluder positioned?
Occluder covers one eye to break fusion
At the beginning of the unilateral cover test, where do you have the occluder positioned?
Occluder is to the side of the eye which you will then cover to break fusion
Is phoria a property of one eye or both eyes?
Unlike strabismus, phoria is a property shared by two eyes.
Define orthophoria
Phoria has a size of zero.
Even with fusion broken, the eye behind the occluder continues to point at the target, even though it can’t see the target through the occluder. The eyes remain aligned with each other.
Define heterophoria
Any phoria other than zero.
With fusion broken, the eye behind the occluder no longer points directly at the target. The eyes are misaligned with each other when fusion is disrupted.
Define exophoria
In the phoria position (when covered), the eye does not turn in (converge) enough to be pointing at the target. The direction of deviation is outward.
How would you observe an exophoria?
When removing the occluder from the covered eye, the eye would be observed moving inward revealing that it was deviated outward.
Define esophoria
In the phoria position (when covered), the eye does not turn out enough to be pointing at the target. It is converged too much. The direction of deviation is inward.
How would you observe an esophoria?
When removing the occluder from the covered eye, the eye would be observed moving outward revealing that it was deviated inward.
Define hyperphoria
Eye that is deviated upward
Define hypophoria
Eye that is deviated downward
When describing vertical deviations, you always specify both the ______ and the ____.
Direction and eye
For vertical phorias, the convention is to always specify the _____ eye.
a. hyper
b. hypo
a. hyper
When do you refer patients with phorias?
When the phoria is large or vertical
Define exotropia
Occlusion of one eye causes the other eye to move medially. This eye that moves has an exotropia.
Define esotropia
Occlusion of one eye causes the other eye to move laterally. This eye that moves has an esotropia.
On the unilateral cover test, when you cover the patient’s OD, his OS does not move. When you cover his OS, his OD does move. What kind of deviation does he have?
Right tropia
During the ACT, when you move your occluder quickly from the OD to OS, you see the OD move inward. When you move your occluder quickly from the OS back to the OD, you see the OS move inward. This patient has a
exophoria
