MCQS In OCULAR MOTILITY - COVER TESTS Click Here
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Link:--The Cover Test
-The Uncover Test
-The Cover-Uncover Test
-The Alternate Cover Test
-Bonus: Self-Assesment [MCQs]
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The Cover Test
This module uses animations extensively to demonstrate important concepts. The material is best viewed online in a browser window. Viewing the material on a printed page may not give sufficient information for a good understanding of the material.
The cover test is a simple procedure, using only the occluder, that is used to detect the presence of an eye muscle imbalance known as a tropia.
A patient who does not demonstrate a deviation of eye alignment is termed "ortho" or "orthophoric".
A tropia is an eye turn or deviation that the patient has no, or very little, control over. The patient is unable to keep the eye straight with the power of fusion. Even though there is such a thing as an intermittent tropia, a tropia is a manifest deviation, meaning it is evident upon inspection and is not hidden.
A phoria is a muscle imblance that is hidden by fusion. The eyes remain straight as long as fusion is present. The phoric deviation only becomes evident when fusion is disrupted.
Identifying deviations by direction and by deviating eye
While the fellow eye fixes on a visual target, the tropic eye deviates either toward the nose (esotropia), temporally (exotropia), superiorly (hypertropia), inferiorly (hypotropia), or a combination of a horizontal and a vertical deviation.
The deviation is further identified by the eye that is deviating.
A hypotropia is a bit confusing because they may be labeled as a hypertropia of the other eye. For example, a left hypotropia may be labeled as a right hypertropia, even though the left eye is deviating and the right eye is fixing. To avoid confusion only use the RHT to indicate a right eye that is deviating upward. If the left eye is deviating downward you can simply write out "left hypotropia".right esotropia (RET)
right exotropia (RXT)
right hypertropia (RHT)
left esotropia (LET)
left exotropia (LXT)
left hypertropia (LHT)
alternating esotropia (ALT ET)
alternating exotropia (ALT XT)
An alternating tropia occurs when a patient always has a deviating eye, but can and does fixate with either eye. For example, the patient may be fixing with the right eye and the left eye may be deviating outward (XT). A moment later the patient may switch fixation to the left eye and the right eye will move to an outward deviation.
A combination left exotropia and left hypertropia might be labeled:
LXT with LHT.
When performing the cover test, our job as technicians is to answer the question: Is there a tropia present? Yes or no. If the answer is yes, we should identify (name) the tropia. The Uncover Test (Sections 2 and 3) and the Alternate Cover Test (Section 4) will be used to detect a phoria.
Have the patient view a distant target (the test is also performed at near).
While you observe the right eye, use the occluder to cover the left eye. One of two things will happen:
1) If the right eye does not move and remains fixed on the visual target, then the right eye is not tropic.
2) If the right eye is observed to move in order to take up fixation, then the eye is tropic and the tropia is identified according to the direction the eye moved from, and which eye it is that moved.
Look at the two demonstrations below. In the top demo a right esotropia (RET) is demonstrated.
The patient is viewing a distant target. It is obvious in this example that the left eye is fixing on the target and the right eye is turning in. Small angle tropias are not this obvious. As the demo starts, an occluder moves over the left eye, forcing the right eye to search for the target. The right eye moves to take up fixation. The right eye is moving outward from an inward position, so the deviation is termed a right esotropia.
The demo below illustrates a right exotropia (RXT) revealed by the cover test.
We have checked the right eye with the cover test. Now we complete the cover test examination by testing the left eye.
Remove the occluder from the left eye and allow the patient's gaze to stabilize on the target.
Now cover the right eye with the occluder while you observe what happens to the left eye. As discussed above, the left eye will either remain straight, or it will move from a deviated position to take up fixation.
It is possible that an obviously tropic eye will not move to take up fixation. This typically occurs when the vision is poor in the deviating eye. The eye cannot see the fixation target, so it doesn't pick up fixation. In these cases the tropia is usually so obvious that a cover test is not needed.
A confusing situation for beginners is the patient with an alternating tropia. This patient may fixate first with the right eye and a moment later shift fixation to the left eye, and may do so back-and-forth. As fixation is shifting, the fellow eye moves to a deviated position. You may not even need an occluder for this patient. The trick is to recognize that the patient is shifting fixation from one eye to the other and to observe which way the deviating eye is moving.