The cover test, much like visual acuity, is a cornerstone of the comprehensive optometric exam. It provides me with a snapshot into how the eyes work together, how often they work together (if they don’t always cooperate with each other) and how much control the patient has over their binocular status. When I was in school, one of my professors called this test “the prince of tests”. I had not been out on my externships yet (aka in the real world of optometry) so I did not realize how true this was.
This seemingly simple test gives me a wealth of information such as (but not limited to):
- presence of phoria (uses eyes together) or a tropia (eye turn)
- magnitude of the phoria or tropia
- IF IN THE PRESENCE OF A TROPIA: which eye(s) it affects (laterality)
- intermittent vs constant trope: does the eye turn all the time or some of the time?
- fixational abilities: can the patient maintain central fixation with each eye?
- can the patient pick up fixation with the strabismic eye once its uncovered
- how well can the patient maintain fusion?
So what? What does all of this mean? How does this translate to the real world? WHO CARES BESIDES THE OPTOMETRIST?!?!?
How well the patient can hold their binocular posture in my chair gives me an indication as to how well the patient maintains fusion (eyes working together!) in the real world. This is the ultimate goal–to have eyes that work together. If a visually stressful situation promotes the breakdown of fusion easily, then I can assume that the patient’s eyes do not work together well in real world situations, like reading and school environments.
For an idea of what a cover test looks like, click here. Keep in mind for a small child or a patient with less than adult level fixations, other methods can be used to gather similar information.
Most of the information about cover tests is incredibly dry…so I will spare you the details. Leave that to me. Tune in next time for….measures of FUSION!!!