The Hows and Whys of Ocular Motility Testing
Ocular motility disturbances can be a sign of life threatening conditions. Causes of ocular motility disturbances include: Diabetes, Thyroid Eye Disease, Brain Tumors, Strokes, Multiple Sclerosis, AIDS, Myasthenia Gravis, Arteriosclerosis and more. We check ocular motility to determine if there is an underlying medical condition which needs treatment. Evaluation strategies include:
1. Check versions. Versions are binocular movements of both eyes in the same direction. Have the patient look in each of the six cardinal positions of gaze (R, Up and R, Up and L, L, Down and L, Down and R). These six cardinal positions of gaze require each extra ocular muscle in each eye to work at some point in time, so if the patient's versions are 'full' (meaning both eyes can look in each of those gazes) and the patient has no complaints of diplopia, you are done with ocular motility assessment. If the patient's versions are not full or the patient has complaints of double vision, you must perform more testing.
2. Perform cover tests. The Cover/Uncover test is used to determine if there is a tropia. A tropia is present with both eyes open and is a sign of an underlying condition. Have the patient fixate on a distant fixation target. Cover OD, then uncover OD. Allow the patient to be binocular in between the times you cover the eye. Repeat at least three times OD. If OS moves to take up fixation when you cover OD you have discovered a tropia. Look at the uncovered eye.
If the uncovered eye moves in to take up fixation it's an exotropia of the uncovered eye. If it moves out, it's an esotropia. If it moves down, it's a hypertropia. This can be confusing. Here's a take home message: We are observing the uncovered eye recover from it's deviation - not observing the deviation itself. Therefore, if the uncovered eye moves in to take up fixation that means it was deviated out (an exotropia)
The Cross Cover (aka Alternate Cover) test is used to detect a phoria. A phoria is only present when you cover one eye. It's a latent (hidden) deviation kept in check by binocular fusion. Phorias are normal, however some patients have "decompensated phorias", where they can no longer control their phoria. These patients may need prism. Here's how to perform this test: With the patient looking at a distant fixation target alternately cover one eye, then the other. DO NOT allow the patient to be binocular (in this test you must break fusion). Look at the eye as you uncover it. If the eye moves as you uncover it, you have revealed a phoria. if the uncovered eye moves in, it's an exophoria. If it moves out it's an esophoria and if it moves down it's a hyperphoria.
3. Other tests to identify and measure deviations include Hirshberg and Krimsky tests, Bielschowsky head-tilt test, Worth 4 Dot test and Maddox Rod test. The scope of this text precludes covering these tests in detail.
By checking versions and performing cover testing most deviations can be revealed. Further motility testing is required to determine the magnitude of the deviation, the most affected muscle and whether the muscle is overacting or underacting.