• tests for a phoria

• When a phoria is present it means that there is a muscle imbalance,  but the eyes are kept in the aligned position by the power of fusion.  The goal of the testing procedure is to disrupt fusion (cover) and observe which direction the covered eye moves to take up fixation when double vision occurs (uncover).

• In the Cover Test we were interested in what was happening with the uncovered eye. This time we are interested in what is happening with the covered eye.

Method

1. Both eyes appear to be fixing (or straight) when not covered.

2. The patient is instructed to look at the distant target. We cover the left eye and leave it covered for about 10 seconds. We have disrupted fusion.

3. By way of illustration let’s say that the left eye, which is covered and is not fixing, now drifts to it’s resting position,  which happens to be outward. When covering,  be sure to pause long enough with the eye covered to allow the covered eye time to drift to it's resting position.

4. We now uncover the left eye.

5. At this moment (which indeed may be a very short moment) the right eye is fixing but the left eye is not fixing and has drifted outward.  At this moment the patient has.......you guessed it, double vision. This is an emergency bell to the brain that some realignment needs to be done.

6. An electro-mechanical process now goes into effect which realigns the eyes,  restores binocular fixation, and regains single vision.

7. The physiological action that you will observe is that the left eye will move from its outward position in an inward direction to again take up fixation.

• How do we name or describe what we have observed? It is an exophoria. The left eye has moved from its outward (exo) position in an inward direction to take up fixation. If the eye had moved from an inward (eso) resting position in an outward direction to take up fixation it would be an esophoria.

• If the eye had moved from an upward (hyper) resting position to take up fixation it would be a left hyperphoria.

• If the eye had moved from a downward (hypo) resting position it would be a right hyperphoria. Even though it seems logical to refer to it as a left hypophoria this condition is usually identified by the eye that is most upward.

• Please note that nothing has been mentioned about a left or right esophoria, or a left or right exophoria. That is because this further identification is unnecessary when referring to a horizontal phoria.  If there is a left exophoria present then there is automatically a right exophoria present. A phoria describes the resting, non-fixating relationship between the two eyes. The terms left or right exotropia are used because left or right describes which eye is deviating when both eyes are not covered.  In the case of a phoria,  both eyes fixate (do not deviate) when the eyes are not covered.