Four of them are rectus muscles, meaning that they yank the eye straight back toward the origin of the muscle. These
four muscles are either medial, near the nose, lateral, near the temple, superior, above the eye, inferior, below the
The other two muscles are oblique muscles which means that they pull the eye at an angle causing a slight toric motion.
These two muscles are the inferior oblique and the superior oblique muscles.
Thus the six eye muscles and motions are:
Inferior rectus (IR) – down
Superior rectus (SR) – up
Medial rectus (MR) – in toward nose
Lateral rectus (LR) – out towards temple
Superior oblique (SO) – depresses and rotates the eye
Inferior oblique (IO) – turns inward and rotates the eye
Versions and Ductions
Versions are a tropia or phoria of both eyes in the same direction. Ductions are a tropia or phoria of one eye alone.
Tropias and Phorias
A tropia is deviation which is always present. Tropias can be seen when a patient is trying to fixate on an object. Both
eyes do not work together. This results in a loss of fusion. Which is the ability of the eyes to work together. When
eyes are not focusing on the same target then they will have double vision
A phoria is a deviation which has to be teased out a little. A patient may look like they are fixating on an object, but
when the cover test is preformed, when fusion is disturbed, the eye will deviate.
Cover tests are used to disrupt fusion. There are two kinds of cover tests the cover/uncover test and the
alternate cover test.
The cover/uncover tests for phoria. It is preformed by covering one eye
at a time and seeing if the uncovered eye deviates.
The alternate cover test will test for total deviations (phobia + tropia).
Stereoacuity is the ability to detect distances in depth. The eyes use environmental clues to determine what objects are
close and which are far away. Depth perception is not the same as stereoacuity. A monocular patient can have depth
perception, but not stereo vision. Stereoacuity is measured in seconds. The less amount of time the better the stereo
Nystagmus is the random jerking of the eyes. When a patient has nystamus one eye should not be covered while testing
visual acuity. Instead try to fog out the eye or use a lens with will effectively blur the eye that would normally be