Question 73 of 100

(demo test)

An eye that is constantly turned away from the nose is in exotropia. The prefix exo- means the eye goes out, away from the nose. The ending -tropia means the turn is manifest, so it is there under normal conditions with both eyes open. This patient has a right exotropia, because it is the right eye that rests outward.

Misaligned eyes are called strabismus. Two quick tests sort it out. The corneal light reflex tests are the simple ones. You shine a light and compare where the reflection sits on each cornea. If the reflex is displaced nasally, there is an exodeviation. If it is displaced temporally, there is an esodeviation. These tests are easy and need little cooperation, but they give less information than cover testing, so cover testing is used whenever possible. In the cover-uncover test you cover one eye and watch the other. Refixation movement means a tropia. If nothing moves, you go on to the alternate cover test to look for a hidden phoria. The alternate cover test cannot tell a tropia from a phoria on its own, which is why it always comes second.

Say the direction first and the eye second, so nothing gets lost in the chart. Use a dim light or an interesting target, never a bright light, because bright light bothers the patient. Start the motility exam by watching the eyes as the target moves into the six cardinal positions of gaze. If the two eyes move normally together, there is no need to test one eye at a time. Strabismus matters because it prevents fusion, the ability of the brain to merge the two images into one, and adults then notice double vision. Sorting and naming horizontal deviations is part of the COA ocular motility testing content area.

Incorrect Answers

• A. Esotropia is the opposite horizontal direction. The eye turns inward, toward the nose, and the light reflex is displaced temporally.
• C. Hypertropia is a vertical deviation with one eye turned up. This eye drifted sideways, not upward.
• D. Hypotropia is a vertical deviation with one eye turned down. Again, the turn described here is horizontal.

Testing Pearls

• Exo- means out and eso- means in; hyper- is up and hypo- is down.
• A nasally displaced corneal light reflex signals an exodeviation.
• A temporally displaced corneal light reflex signals an esodeviation.
• Cover testing gives more information than light reflex testing and is preferred.
• The prism and alternate cover test measures the deviation in prism diopters.

References

1. American Academy of Ophthalmology. Ophthalmic Medical Assisting: An Independent Study Course. Chapter 9, Ocular Motility.