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Clinical Skills > Cover Tests > Flashcards

Cover Tests Flashcards

1
Q

Cover Test (CT) is done to determine what 5 things?

A
  1. presence of a deviation (phoria or tropia)
  2. laterality/which eye (unilateral or alternating)
  3. frequency of the deviation (constant or intermittent) 4. direction of the phoria or tropia
  4. magnitude (size) of the deviation.
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2
Q

What is orthophoria?

A

Orthophoria: the perfect alignment in the absence of a stimulus for fixation.

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3
Q

What is heterophoria/phoria?

A

Heterophoria/phoria: the tendency for the eyes to deviate when fusion is blocked

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4
Q

A small phoria is common in most people. How is it overcome?

A

By fusion

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5
Q

What is esophoria? What is exophoria?

A

A “posture” slightly inward is esophoria and a posture slightly out is exophoria.

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6
Q

What is decompensating phoria?

A

When motor fusion is no longer enough to overcome a phoria, it is called a decompensating phoria. This could result in discomfort or diplopia.

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7
Q

What is heterotropia/tropia?

A

Heterotropia/tropia: this is a manifest deviation Visual axes of both eyes do not intersect at fixation. Leads to diplopia or suppression of the deviated eye.

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8
Q

Why does a tropia occur?

A

A tropia could occur due to some of the following reasons:

  1. Anisometropia (difference in refractive errors between the two eyes)
  2. Abnormality of the extraocular muscles or strabismus
  3. Eye disease
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9
Q

Cover-Uncover test (Unilateral Cover Test): This helps to differentiate…

A
  • presence of a deviation (phoria or tropia)
  • laterality/which eye (unilateral or alternating)
  • frequency of the deviation (constant or intermittent)
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10
Q

Which type of cover test is done first?

A

The cover-uncover test is done first.

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11
Q

Alternating cover test: This is to determines the

A
  1. direction of the phoria or tropia

2. magnitude (size) of the deviation

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12
Q

True or False: Cover test is done at distance and near..

A

True

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13
Q

What does the “cover” show?

A
  1. The “cover” shows if the deviation is a phoria or a tropia. (presence)
  2. It evaluates the visual axis of each eye when both eyes are viewing a target.
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14
Q

In the cover-uncover test, which eye do you look at?

A

You look at the eye that is NOT covered.

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15
Q

The cover-uncover test evaluates:

A

Phoria – the visual axis of both eyes are aligned on the target with both eyes open.
Tropia – the visual axis of one eye is aligned on the target while the other is misaligned with both eyes open.

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16
Q

What will you see in a cover-uncover test when there is phoria?

A

Phoria: visual axis of both eyes will stay aligned on the target

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17
Q

What will you see in a cover-uncover test when there is tropia?

A

Tropia: visual axis of one eye was on the target, the other is misaligned. Now it has to move to pick up fixation

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18
Q

What does the “uncover” in the cover-uncover test show?

A

“Uncover” shows if a tropia is alternating or unilateral tropias. (laterality)

“Uncover” also shows if a tropia is constant (always present) or intermittent. (frequency

Focus on the eye that is not occluded to determine if it picks up fixation.

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19
Q

What is a unilateral tropia?

A
  1. A unilateral tropia (Right or left tropia) is when one eye usually fixates when both eyes are open.
  2. The tropic eye only fixates when the preferred fixating eye is occluded.
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20
Q

What is an alternating tropia?

A

An alternating tropia is when the patient is able to keep either eye (visual axis) on a target with both eyes open.

21
Q

What is the equipment needed for the cover-uncover test? The 6 things are:

A

Equipment:

  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
22
Q

Explain the purpose to the patient of the cover-uncover.

A

“I want to make sure your eyes are aligned properly.”

23
Q

Does the patient of the examiner hold the occlude and prisms in the cover-uncover test?

A

Sit or stand in a way that you can see the eyes but does not block the patient’s fixation on the targets. Hold the occluder and the prisms.

24
Q

In the cover-uncover distance test, isolate a letter that is _____ or _____ lines ____ than the BCVA in the poorer seeing eye.

A

At distance, isolate a letter that is one or 2 lines larger than the best corrected visual acuity (BCVA) in the poorer seeing eye.

Target letter could be between 20/25 or 20/40 depending on the entering VA or BCVA.

25
Q

How far away should the target be in a near cover-uncover test?

A

At near, hold an accommodative target at 40cm.

It could be a letter that is one or 2 lines larger than the BCVA of the poorer seeing eye. It could be a target of comparable detail/size (about a 20/30 size). The patient may hold the target.

26
Q

In a cover-uncover test, tell the patient to look at the target and keep it clear. How do you assess fixation?

A

To assess fixation, determine if the patient 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.

27
Q

What does it mean is there is no movement is the right eye when the left eye was covered?

A

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.

28
Q

How much time do you allow between occlusions?

A

Remove the occlude, and allow 2-3 seconds for both eyes to resume their relationship with each other (to pick up binocular vision).

29
Q

Do you do the cover-uncover test once or repeatedly on each eye?

A

Repeat a few times to verify the position of the right eye when the left eye is occluded. Then repeat the above steps occluding the right eye to evaluate the left eye

30
Q

What does the patient have if there were no movements seen when either eye was covered?

A

If there were no movements seen when either eye was covered, this patient has a phoria. Implying that under binocular conditions, with stimulus both visual axes are aligned.

31
Q

What does the patient have if there were movements on the cover-uncover test?

A

If there was any movement on unilateral cover test, the patient has a tropia. To determine if it is a unilateral or alternating tropia, observe the movement of the uncovered eye.

32
Q

What does the alternating cover test determine?

A

Determines the direction and the size of the deviation.

33
Q

What are the steps in the alternating cover test?

A
  1. Tell the patient to look at the target and keep it clear.
  2. Place the occlude in front of the right eye for 2-3 seconds to break binocular fusion.
  3. Quickly alternate and move the occlude to the left eye, observing the right eye you just uncovered for direction of movement.
  4. Pause and leave the occluded in front of the left eye for 2-3 seconds.
  5. Quickly move from the left eye to the right eye, observing the left eye that was just uncovered.
  6. Repeat several times. Make sure one eye is always covered to ensure disruption of fusion.
  7. Identify the direction of the deviation.
34
Q

How do you measure the deviation?

A
  1. Put prism in front of one eye and watch the other.
  2. Continue to move the occluder back and forth while increasing the prism until you no longer see movement.
  3. The deviation is neutralized at the amount of prism where both eyes appear aligned and there is no more movement on alternate CT.
35
Q

What prisms do you use for what deviation?

A 
Exo (eye out) BI 
Eso (eye in) BO 
Hypo (eye down) BU 
Hyper (eye up) BD 
Ortho (alignment) Verify by using BI and then BO
  • Measure the deviation with prisms (it is measured in Prism diopters)
  • Place the prism (proper base) over the eye as close as possible
  • Repeat the alternating cover test while increasing the prism until no more movement is seen
36
Q

What do you record with the cover-uncover test?

A
  1. Indicate if it was done with prescription (cc) or without correction (sc).
  2. Record distance (D) and near (N) findings separately.
  3. Record the amount of prism that was required to neutralize the deviation.
  4. Record the direction of the deviation
  5. Record if it is a phoria (P) or tropia (T) (Presence of a deviation)
  6. Record an intermittent tropia with a parentheses (T) (Frequency)
  7. Record the amount of prism measured in Prism Diopter (Magnitude)
37
Q

How do you record the directions of deviation?

A 
E for Esotropia or Esophoria 
X for Exotropia or Exophoria 
RH for Right Hypertropia or hyperphoria
LH for Left Hypertropia or hyperphoria 
Ortho for no deviation
38
Q

When recording a tropia, record

A
  • right as “R”
  • left as “L” - alt as alternating. (laterality)
  1. Right or left must be recorded for all vertical phorias and tropias.
  2. Right or left “hyper” or “hypo” is usually for a phoria or tropia. Hyper deviations are recorded by convention
  3. Horizontal phorias are usually not recorded like this since the phoria is a relationship between the 2 eyes.
39
Q

Deviations are comitant or noncomitant. What is comitancy?

A

Deviation size remains same (or within 5pd) in all positions of gaze. Implying no muscles are underacting or overacting.

40
Q

What is noncomitancy?

A

Deviation size changes in different positions of gaze. Due to an over action or under action of one of multiple muscles.

41
Q

To determine comitancy, CT is done in ____ positions of gaze.

A

ALL

42
Q

What is the Hirschberg test?

A

This is a rough objective estimate and measurement of a deviation/strabismus. Useful in young and uncooperative patients.

43
Q

What are the instructions to do the Hirschberg test?

A

A penlight is held straight in front of a patient’s face. The patient is instructed to fixate on the penlight with both eyes open.

44
Q

What are the results of the Hirschberg test if it is normal? And abnormal?

A

In the absence of strabismus, the corneal reflex should be centered in both eyes. In the presence of strabismus, the reflex will not be in the center of the deviated eye.

45
Q

With the Hirschberg test, for 1 mm of estimated deviation, it is approximately a deviation of ___ prism diopters

A

22

46
Q

What is the Krimsky test?

A

This is the combination of the Hirschberg test with prisms to determine the angle of deviation.

47
Q

What are the instructions to do the Krimsky test?

A

Prisms are placed in front of the fixating eye until the corneal reflexes are symmetrical. In the Prism Reflection Test, the prism is held in front of the deviated eye until the corneal reflex is symmetrical.

48
Q

With the Krimsky test, what prisms are used for esotropia and exotropia?

A

Base Out prism is used for esotropia

Base In prism is used for exotropia

Clinical Skills (7 decks)

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