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Eye muscle testing is a simple but important part of a comprehensive eye examination. It is performed to evaluate any weakness or other defects in the extraocular muscles that may result in double vision or uncontrolled eye movements. The test itself involves moving the eyes in eight different directions to evaluate the proper functioning of the eye muscles. This can indicate optical conditions such as strabismus, commonly known as being cross-eyed, or other issues with eye functioning.
| Characteristics | Values |
|---|---|
| Objective | To reveal restricted or abnormal eye movement |
| Test Name | Extraocular Muscle Function Testing, Ocular Motility Testing |
| Test Procedure | Moving the eyes in eight different directions while the head is held straight |
| Distance of the Object from the Patient | 12-16 inches or 40 centimeters |
| Movement of the Object | Up, down, and side to side in an H-shaped pattern |
| Abnormalities | Strabismus, double vision, myasthenia gravis, hyperthyroidism, nerve damage, amblyopia, Duane's retraction syndrome |
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What You'll Learn
Testing for double vision
Double vision, or diplopia, is a common vision problem that can be caused by a range of eye conditions. It occurs when a person sees two images instead of one. It can happen in one or both eyes. In some cases, the two images are completely separate, and in other cases, they overlap.
Double vision can be caused by a problem with the eye muscles, the nerves that control eye movement, or the neuromuscular junction—the space where nerves connect to the muscles they control. It can also be caused by neurological conditions, such as myasthenia gravis or multiple sclerosis, or it may be associated with a systemic disorder, such as hyperthyroidism.
To test for double vision, a doctor will perform a series of painless tests to evaluate your vision and determine if the double vision is binocular or monocular and if your eyes are misaligned. They may ask you to look through a prism-shaped tool, which bends the path of light that the doctor shines into your eye, allowing them to measure the degree of misalignment. This helps them determine the cause of the double vision and the best way to correct it.
During an eye exam, a doctor will also evaluate how looking in different directions affects double vision. They may ask you to move your eyes around an imaginary clock face from 12 to 6 and back to 12 again, noting if your vision is better or worse at any position. They may also ask you to tilt your head to the right and left to see if these positions improve or worsen your eyesight.
If double vision is caused by eye muscle problems or vascular issues, eye exercises may help reduce symptoms. These exercises can include holding an object, such as a pen or pencil, at arm's length and slowly bringing it closer to your nose while trying to keep it as one image.
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Eye movement in eight directions
During the test, the patient is asked to sit or stand with their head up and looking straight ahead. The healthcare provider will hold a pen or another object about 16 inches or 40 centimeters in front of the patient's face. The provider will then move the object in several directions, including up, down, and side to side in an H-shaped pattern, and ask the patient to follow the object with their eyes without moving their head. The patient's eye movements should be smooth and coordinated.
The test can also be performed with a cover/uncover test, where the patient looks at a distant object, and the tester covers one eye and then uncovers it after a few seconds. The patient is asked to keep looking at the distant object, and the way the eye moves after it is uncovered may indicate problems. This test is then performed with the other eye.
Another variation of the test is the alternate cover test, which is similar to the cover/uncover test but with some differences. In this test, the patient focuses on the tester's nose while one eye is covered and uncovered quickly. The patient's eye movements are then observed to detect any abnormalities.
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H-shaped pattern test
The H-shaped pattern test is a part of extraocular muscle function testing, which examines the function of the eye muscles. The test involves moving the eyes in eight different directions in space to evaluate the proper functioning of the extraocular muscles of the eyes.
To perform the test, the patient is asked to sit or stand with their head up and looking straight ahead. The healthcare provider will hold a pen or another object about 16 inches or 40 centimetres in front of the patient's face. The provider will then move the object in several directions, including up, down, left, and right, as well as diagonally, forming an H-shaped pattern. The patient is instructed to follow the object with their eyes, without moving their head.
The H-shaped pattern test is particularly useful for assessing ocular motility because each cardinal position is primarily obtained by the action of one muscle. For example, the elevation of the eye from the primary gaze is accomplished by the actions of both the superior rectus and the inferior oblique muscles. However, the elevation of the abducted eye is primarily accomplished by the superior rectus, while the elevation of the adducted eye is primarily accomplished by the inferior oblique muscle.
By observing the patient's eye movements during the H-shaped pattern test, healthcare providers can identify any weaknesses or defects in the extraocular muscles that may result in uncontrolled eye movements. This test can also help determine the cause of double vision, or diplopia, which can occur in one or both eyes.
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Cover/uncover test
The cover test is a critical component to understanding how a patient's eyes move and work together. Abnormal eye positioning could be the cause of numerous symptoms, such as double vision (diplopia), eye strain (asthenopia), reading difficulties, and headaches. The test is performed in two steps.
Firstly, ensure there is sufficient lighting in the room so that the examiner can clearly see the patient's eyes. The examiner should sit approximately 30 cm away from the patient to ensure they are able to observe their eye movement. The patient should be asked to look at a letter or a Snellen chart for distance testing. The cover/uncover test involves one eye being covered. The examiner should instruct the patient to "keep watching the letter while I cover your eye". The examiner then covers one eye of the patient with their hand or a paddle and observes the movement of the other eye.
The cover is then removed, and the examiner looks for movement of the previously covered eye. When the cover is placed over the eye, the examiner is looking for strabismus (also referred to as squint or tropia). When the cover is removed, the examiner is looking for a phoria (the "natural" eye position of a patient when fusion is disrupted). The movement and position of the eye under the cover when the paddle is removed should be observed and the process is repeated until a diagnosis can be confirmed.
The cover test is typically performed by orthoptists, ophthalmologists, and optometrists during eye examinations. The test is used to determine the presence, type, and magnitude of ocular misalignment (strabismus). The two primary types of ocular deviations are the tropia and the phoria. A tropia is a misalignment of the two eyes when a patient is looking with both eyes uncovered. When a patient has a manifest strabismus, the uncovered eye will take up fixation when the fixing eye is covered.
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Ocular motility exam
The ocular motility exam is a simple but important part of an ophthalmic exam. It is also known as an extraocular muscle function test, which examines the function of the eye muscles. This test is performed to evaluate any weakness or other defects in the extraocular muscles that may result in uncontrolled eye movements.
The test itself is simple. The patient is asked to sit up straight and stare at an object in front of them, usually a pen, fixation light, or small picture held 12-16 inches (40 centimetres) away. The provider will then move the object in several directions and ask the patient to follow it with their eyes without moving their head. This can be done in eight or six specific directions, including up, down, left, and right. The H-pattern, which involves moving the object up and down and side to side in an H shape, is particularly useful for assessing ocular motility as each cardinal position is primarily obtained by the action of one muscle.
A test called a cover/uncover test may also be done. The patient will look at a distant object, and the person conducting the test will cover one eye, wait a few seconds, and then uncover it. The patient will be asked to keep looking at the distant object. How the eye moves after it is uncovered may indicate problems. This test is then repeated with the other eye. A similar test is the alternate cover test.
The ocular motility exam can help determine the cause of double vision, or diplopia, which can occur in one or both eyes. Potential muscular causes of double vision include strabismus ("cross-eyed"), myasthenia gravis (a neuromuscular condition causing muscle weakness), a side effect of hyperthyroidism (Graves' disease), and damage to the nerves surrounding the eye muscles.
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