Introduction
In the eye of humans, there are seven extrinsic muscles, called extraocular muscles of the eye. Four are recti, the rest is the superior oblique muscle, and another is the inferior oblique. These muscles coordinate together in various movements of the eyes. Eye movements are not synchronized in certain conditions, such as double vision. The levator palpebrae superioris muscle controls the elevation of an eyelid. Tests for these muscles are known as extraocular muscle function tests.
What Are the Abnormalities Associated With These Muscles?
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Movements of the eye are affected when cranial nerves are damaged. As a result, the examination may reveal abnormalities.
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Damage to the oculomotor nerve (III) causes abnormalities such as double vision, strabismus in which movements of both eyes are not coordinated properly, drooping of eyelids called ptosis, and pupil dilation called mydriasis.
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In addition, due to damage, paralysis can occur, and the lesions may lead to the inability to open the eyes due to damage to the levator palpebrae muscle. Finally, in some individuals, lesions cause discomfort to the patient (to compensate for the pain, some patients keep their heads tilted). When the drooping eyelid obstructs the visual axis, the patient will tilt the head backward in order to visualize the object.
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Double vision also occurs due to damage to the trochlear nerve (IV). Damage to this cranial nerve causes impairment in the superior oblique muscle. Due to this, the eye cannot move properly.
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Double vision also occurs due to damage to the abducens nerve (VI). This causes impairment in the lateral rectus muscle.
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Amblyopia, also called lazy eyes, causes diminished vision in one eye.
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Ophthalmoparesis is an extraocular defect. It occurs when there is a weakness or flaw in one or more extraocular muscles.
How to Examine Extraocular Muscles?
For the initial clinical examination of the extraocular eye muscles, the movement of the eye is examined through the six eye movements:
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Lateral rectus muscle function is tested in the eye's horizontal direction.
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The medial rectus function is tested horizontally and turning (nasally). In the eye down and during eye movement, there is a contraction of the inferior rectus. When eye movement turns up, the superior rectus is contracting.
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The inferior oblique muscle is used in turning the eye up and out.
For turning it down and out, use the superior oblique. Finally, drawing a large H can test all these six movements.
A penlight is shone on the corners of the eye directly. It evaluates and examines weakness or imbalance of the muscles.
What Is the Pulley System?
The movements of the extraocular muscles are coordinated under the influence of the pulley system of the extraocular muscle. Soft tissue pulleys are present in orbit. The pulley system's role is fundamental in the extraocular muscle movement of the eye. Some diseases of the pulley system can cause strabismus. Surgical correction is required in case of defective pulley systems.
What Is the Definition of the Extraocular Muscle Function Test?
Extraocular muscle function testing examines the eye's function of extraocular muscles. In the testing, movement of the eye is performed, and an examination in six different directions by a healthcare provider is done. The alternative names for the extraocular muscle function test are the extraocular movement test and the ocular motility examination.
How to Perform Tests?
In the test, the healthcare provider will tell the patient to sit or stand with the head up and ask to look straight ahead. After proper positioning, the healthcare provider will hold an object or a pen at a distance of 16 inches or 40 centimeters (cm). Then they will do different movements in several directions and ask to follow the object's motion with one eye without movement of the other eye.
In this cover or uncover test, ask to look at distant objects; one eye is covered by the person doing the test. The patient is asked to keep looking at the distant object. Movement of the eye may show a problem when uncovered, then repeat the test in the same manner, and the test is performed with the second eye.
An alternate test is a similar test that may also be done. In this, three to four cycles of covering and uncovering processes are done. First, the same object is seen with one eye, covers another eye, reveals the covered eye, covers the other eye, and repeats the test in three to four cycles. The test is simple and no special preparation is required. It can be performed anytime in the day. No specific time slot is required to do this test and there is no discomfort to the patient during the test as it involves only normal eye movement.
Why Is the Test Performed?
To analyze and evaluate any problem or weakness in the extraocular muscle of the eye. Because these weaknesses or problems may result in future problems such as double vision and uncontrolled eye movement, sometimes rapid eye movement may also occur.
What Are the Normal Results for the Test?
Expected test results are that a person can perform all regular movements of the eyes in all directions without any discomfort or problem.
What Is the Meaning of Abnormal Test Results?
In abnormality, one or many eye movements are restricted or affected. These movement disorders may be due to extraocular muscle abnormalities. In addition, there may be problems in some higher centers, such as the brain that controls extraocular muscle or any related cranial nerve defect.
What Are the Risks Associated With the Test?
There is a simple test of eye movements, so it is non-invasive. Therefore, there is no risk associated with this test.
What Are the Considerations Associated With Tests?
During the test, the patient will be asked to have an extreme left or right position in order to have a small amount of uncontrolled eye movement called nystagmus. Although it is considered normal, the patient will not have any other significant abnormality apart from it.
Conclusion
Extraocular muscle function tests help to evaluate the functions of eye muscles. It is a safe test, and no special considerations are required to undertake the test. The test helps with weakness or any problem in extraocular muscles.
