PC - Heterophoria/tropia - Week 3

Question 1

Describe what happens to the eye when fusion is dissociated.

Answer 1

When an eye is occluded, fusion is dissociated.

During dissociation, the occluded eye adopts a fusion free position.

Question 2

Describe orthophoria. How is this seen clinically.

Answer 2

When fusion is dissociated, the fusion free position of the occluded eye remains in the functional binocular position.
Clinically, the eye does not move upon unoccluding the eye.

Question 3

Describe heterophoria. How is this seen clinically.

Answer 3

When fusion is dissociated, the fusion free position of the occluded eye changes from the functional binocular position.
Clinically, the eye moves upon unoccluding the eye to regain fusion.

Question 4

What kind of eye movements occur during heterophoria? Define each type, and how they are detected clinically.

Answer 4

-Esophoria - when the eye converges upon fusion dissociation. Clinically, the eye will diverge when unoccluded.
Exophoria - when the eye diverges upon fusion dissociation. Clinically, the eye will converge when unoccluded.
Hyperphoria - when the eye elevates upon fusion dissociation. Clinically, the eye will depress when unoccluded.
Hypophoria - when the eye depresses upon fusion dissociation. Clinically, the eye will elevate when unoccluded.
Cyclophoria - when the eye rotates upon fusion dissociation.

Question 5

Define tropia, and the different kinds.

Answer 5

Tropia occurs when the eye is not in the functional binocular position even when unoccluded.
The types are identical to phoria types, but are permanent.

Question 6

Is heterophoria always symptomatic?

Answer 6

No, the eye is usually able to sufficiently move to regain fusion. Sometimes it will struggle however, and this is when it becomes symptomatic, and in need of correction.

Question 7

Consider an eye with any form of tropia. What can poor visual acuity of that eye suggest? How can it be evaluated, and what can this result from?

Answer 7

Poor visual acuity in a tropic eye suggests ambylopia. A pinhole can be used to evaluate this.
If poor vision persists, it suggests this is a result of one eye underdeveloping, and leading to the good eye dominating vision.

Question 8

When testing patients for phoria, it can sometimes disappear entirely, only to sometimes reappear. How can this be?

Answer 8

Phoria can be intermittent.

If the patient is aware of their phoria, they can supress it neurologically.

Question 9

How are ambylopia and strabismus related?

Answer 9

They can both cause the other.

Question 10

When assessing a patient for phoria, is it wise to look at the occluded eye for movement?

Answer 10

No, do not look for movement when the eye is occluded, the patient may become aware and result in intermittent phoria.

Question 11

How should accommodation be controlled during a cover test for phoria?

Answer 11

It should be relaxed, so patient should be fully corrected.

Question 12

What illumination level should be used during a cover test?

Answer 12

The room should be fully illuminated.

Question 13

On a Snell/LogMAR chart, what is the best focus point?

Answer 13

The middle letter above their lowest line.

Question 14

During a cover test, what four things should be determined?

Answer 14

• Phoria or tropia
• Direction of deviation
• Magnitude of deviation
• Speed of recovery

Question 15

Consider alternating cover test vs unilateral cover test, which test tells you what?

Answer 15

Alternating - magnitude of deviation

Unilateral - differentiates tropia from phoria

Question 16

Describe how a unilateral cover test is performed, and how it detects tropia.

Answer 16

A cover is placed over one eye for at least 3 seconds. Tropia occurs if the uncovered eye moves to take up fixation.
When both eyes are unoccluded, one is turned.
When the unturned eye is occluded, the turned eye moves to regain fixation. The unturned eye moves under the cover due to yoked movement.
If the turned eye is occluded, no movement occurs.

Question 17

When doing a cover test, are both alternating and unilaternal always done, or just one or the other?

Answer 17

Both are always done.

Question 18

Describe how an alternating cover test is done.

Answer 18

Occlude one eye for 1 second, and alternate repeatedly.

Question 19

Describe what objective and subjective emasurement scan occur during both cover tests.

Answer 19

Objective - when the practitioner looks for eye movement.

Subjective - when the patient is asked if the target focus moves with (exo) or against (eso) the cover.

Question 20

Define an elevated hyperope.

Answer 20

Elevated hyperopia occurs when someone who is considered emmtropic is actually a 3.00+ hypertrope, but are able to accommodate sufficiently. Hyperopia will become apparent with age.

Question 21

Which cover test is best done first? Explain why.

Answer 21

Unilateral, because alternating may induce temporary tropia, by causing them to tire out.

Question 22

How should prisms be held and for what purpose?

Answer 22

From above over the patient’s eye, for their comfort, and to respect their personal space.

Question 23

When correcting phoria with prisms, what should be done when the prism with which no movement is detected?

Answer 23

Begin with the minimum power for orthophoria, and slowly increase until reversal is seen, and write down the range.

Question 24

Does phoria affect only one eye? How does this affect what eye is corrected with prisms to determine power needed for correction?

Answer 24

No, it is the same for both eyes, so the tests can be done on either eye. This applies to phoria only, prism is placed in front of the tropic eye in tropia.

Question 25

What light level should a maddox rod test be done in?

Answer 25

Dark room.

Question 26

Describe how maddox rods work.

Answer 26

Retinal image is distorted to a point of light perpendicular to the axis of the rod.
It dissociates fusion.
In exophoria, the rod will be on the left of the fixation, right for esophoria.

Question 27

What are 3 advantages of maddox rods?

Name 2 disadvantages.

Answer 27

Advantages
Can be used on children
Good repeatability
Evaluates cyclophoria
Disadvantages
Spot of light is a poor stimulus to accommodation
Small element of fusion may exist

Question 28

What if the patient sees more than one line during a maddox rod test?

Answer 28

Ask them to choose the brightest one, or explain that the test may not be suitable for them due to poor accuracy.

Question 29

Describe the Von Graefe technique for each eye, and what is expected of them if they are orthophoric.

Answer 29

A dissociating prism is placed over one eye.
Right - 6 base up, measuring horizontal deviations
Left - 10 base in, measuring vertical deviations
Line selector used - 6/12
Patient is asked if the image is aligned like buttons on a shirt (6BU) or headlights on a car (10BI)

Question 30

Name an advantage and disadvantage of Von Graefe testing.

Answer 30

Advantage - fine control of prism magnitude

Disadvantage - poor repeatability compared to other tests, limited to primary gaze

Question 31

Describe how a prentice card is used.

Answer 31

6BD prism used, on the right eye.
The card is held at 33cm.
If the arrows align, orthophoria.
If the arrow is on the blue, suggests exophoria, the numbers denote magnitude.
Yellow is esophoria.

Question 32

What is the working distances for near and far prentice card usage?

Answer 32

Near - 33cm

Far - 3m

Question 33

Describe briefly how a maddox wing works.

Answer 33

Dissociation occurs via a septum, one eye sees an arrow, the other sees a tangent scale.

Question 34

What should you always ask a patient to do when you have found a reference prism?

Answer 34

Always ask them to blink, and see if it fluctuates.

If it does, record the range, and always check for reversal.

Question 35

With the Von Graefe technique, what prisms are used to correct phoria?

Answer 35

Rixley prisms.

Question 36

In the clinical exam, what should be done once the patient has been fitted with a dissociating prism?

Answer 36

Occlude each eye, and confirm what the patient sees.