Clinical Examination:
Ocular Motility
This section discusses the evaluation of ocular motility with emphasis on the diagnosis
of specific disorders of motility. Following the introduction are a selection of
interactive abnormal cases of ocular motility. This section requires a browser with
JavaScript enabled, and at least Netscape 3.0 or I.E. 4.0, or above.
Evaluation of Motility
Two principle methods of evaluating ocular motility are:
-
Observation of ocular ductions, which are the actual monocular movements of the
eye, and
-
Observation of binocular ocular alignment, using cover/uncover and alternate
cover testing.
There are six extraocular muscles controlling eye movement: the four rectus muscles
(medial, lateral, superior, inferior), and two oblique muscles (superior and inferior).
While the medial and lateral rectus muscles are fairly straightforward in their respective
adduction (inturning) and abduction (outturning) of the eye, the remaining four muscles
are more complex. The superior and inferior rectus, and the superior and inferior oblique
muscles each have primary and secondary actions, depending of the position of the eye.
This is illustrated by the drawing below:
The right eye in the orbit is shown, from a superior view. Note that while the eye is
directed straight ahead that the superior rectus attaches to the eye at an angle.
Similarly, the superior oblique has an angled insertion (from the trochlea near the
superior orbital rim). Because of this angling, the superior rectus will act primarily as
an elevator of the eye especially when the eye is abducted. The superior oblique more
strongly will depress the eye when it is adducted, and will rotate the eye torsionally
when abducted (twists the eye inward.)
Knowledge of this anatomy can aid in determining which muscles are malfunctioning in
different positions of gaze. Examples of abnormal ocular motility patterns are
demonstrated below:
Cover/Uncover Testing
Alternate Cover
Testing
Cover/Uncover and Alternate Cover Testing examine the
binocular relationship of the eyes. In these tests, the patient is asked to fixate on a
distant object (near testing can be done as well). The patient's eye are then observed. If
they appear to be obviously misaligned, there will be typically one eye that fixates, and
the other eye will either deviated outward (exotropia), inward (esotropia), or upward
(hypertropia). There may be one eye that dominates fixation, or this may switch freely
between the eyes. If an occluder is placed over the fixating eye, the deviated eye will
rapidly refixate. Thus, we look for movement of the non-covered eye. If we then rapidly
switch to the other eye, the previously covered eye will refixate.
By the nature of the
direction of these refixation movements, we can identify the problem, and measure it using
prisms. Some examples are shown below. In each example, move the mouse pointer over the
eye to cover, and then switch back and forth.
Esotropia
In this example, the left eye is obviously initially
inturned. When the fixating eye is covered, the other eye immediately moves outward. Since
both eyes fixate equally well, this would be an alternating esotropia.
Exotropia
In this example, the outturned eye
refixates inward when the other is covered. This is an example of alternating
exotropia.
Esotropia with preferential fixation
With
alternate cover testing, this initially may seem to be a simple esotropia.
However, if the left eye is covered, and then the cover is moved away from
both eyes, the left eye will regain fixation. Both eyes exhibit movement in
this refixation.
Vertical deviations:
Hypertropias or Hypotropias
This demonstrates a left hypertropia (usually the problem is named in relation
to the hypertropic eye rather than the hypotropic one.) Note that when the
cover is shifted onto the right eye that the left eye rotates downward, and
when it is shifted on the left eye that the right shifts upward.
Further discussions and
demonstrations of vertical misalignments are discussed on a separate page,
Vertical Misalignments. Also discussed on that page
is the Parks - Bielschowsky's 3 - Step Test for the determination of a single
paralytic vertical muscle.
Evaluation of Phorias
using Cover-Uncover Testing
A phoria is a latent ocular
misalignment held in check by fusion, which is the ability of the eyes to
align themselves so that each is seeing the same image. If fusion is broken by
covering one eye, the latent deviation becomes revealed, and the covered eye
may turn in (esophoria) or turn out (exophoria). Anything that breaks fusion
may reveal an underlying phoria, such as fatigue, inattention (daydreaming),
or bright lights.
Exophoria
In this example, the eyes initially appear aligned. When one eye is covered,
and then uncovered a refixation movement is observed. This is an exophoria.
Dissociated Vertical
Deviation
A dissociated vertical
deviation is similar to a phoria in that the eyes remain aligned until
something breaks fusion between the two eyes (covering one eye, fatigue,
inattention, etc.) The covered eye then drifts upward. When it is uncovered
again, it drifts back down into position, without any movement of the other
eye. This is commonly bilateral.
Ocular Movement
Disorders
In these examples, move the mouse
pointer over the eyes and within the box in the direction that you want them
to look.
Third
Cranial Nerve Palsy
With the left eye fixating, the right eye is initially abducted and rotated
downward (due to unopposed action of the lateral rectus and superior oblique
muscles). The paretic eye cannot adduct past midline, nor elevate past
midline. Note that in a complete Third Nerve Palsy the eyelid would also be
nearly closed from ptosis, and the pupil might be dilated and unreactive.
Sixth
Cranial Nerve Palsy
In a Sixth Cranial Nerve
palsy (left sided, above), the affected eye generally cannot abduct (outturn) past midline, and it
is usually somewhat inturned when the other eye is fixating straight ahead.
(Due to the unopposed action of the medical rectus muscle.)
Orbital Floor
Fracture with Inferior Rectus Entrapment
In this example, the left inferior rectus muscle is trapped in an orbital
floor fracture. Thus is tethers the eye from looking upward in nearly all
positions of gaze.
