Eye Muscle Anatomy,
Myokymia, and Muscle Problems
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Have you or your patients ever experienced that annoying, involuntary eyelid muscle twitching that seems to come and then go away? This is called a tic, or more technically a myokymia. Patients who come into an eye care professional’s office for this problem are often concerned that there may be a serious problem that is occurring to their eyes. Some patients come into my office believing that they may be suffering from a stroke or worse. Many patients have never experienced any problems resembling this and sometimes they think of the worst case scenarios. Usually, it is a benign and a self-limiting condition and is not associated with a disease process.
Muscles are the workhorse of the body. Muscles consist of muscle tissues that are made of special cells called muscle fibers. Muscle tissue has the ability to contract, resulting in the contraction and the movement of muscles. There are three categories for muscle: voluntary, involuntary and cardiac. The contraction of muscles can be under voluntary control or involuntary control. The movement of an arm or leg would be considered voluntary movement – you need to think of the action before it happens. Food that moves through the gastrointestinal tract is aided by involuntary muscle control – you do not have to think about digesting a meal because it happens automatically or via involuntary muscle contractions. There are several types of muscles; striated skeletal, striated cardiac, and smooth. Skeletal muscle comprises the great mass of the human musculature. It has well-developed cross-striations, does not normally contract in the absence of nervous stimulation, and is generally under voluntary control. Cardiac muscle also has cross striations but is different in character due to the presence of pacemaker cells that discharge spontaneously and uniformly. A distinguishing characteristic of cardiac muscle tissue is that it is able to maintain its contractions without fatigue. Smooth muscle lacks cross-striations and is most often found in the abdominal cavity and the intestines.
Conditions that can affect muscles include infectious myositis, myopoathy, trauma, paralysis, neuromuscular diseases, lacerations, contusions, myocarditis, myocardial infarction, and cardiac arrhythmia. Any neurological condition, nerve paralysis, central nervous system problem, or peripheral nervous system problem can also cause muscle problems. The nerves are the “electricity” that allows the muscles to know how to react.
In the eyelid, myokymia is sometimes referred to as a chronic blepharospasm. It is an involuntary spontaneous, small muscle contraction or tic of the eyelid muscles without the presence of muscular atrophy or muscle weakness. It is a local “quivering” of a few muscle bundles within a muscle. It can occur in normal individuals and can start then stop spontaneously. Patients may notice a sporadic “jumping” or “twitching” of either eyelid. It can sometimes last up to three weeks per incident.
Every movement of the eyes requires the cooperation and coordination of several muscles. These muscles are referred to as the extraocular muscles and encircle the eye or the eyelids. The effect of the muscle coordination is expressed in the different positions into which the eyes may be placed by their action. The eyelid muscles and nerves that encircle the eye include the levator palpebrae superioris which is innervated by the 3rd cranial nerve, the oculomotor nerve. Muller’s muscle is innervated by the sympathetic nervous system. It is a layer of non-striated muscle fiber that runs vertically within the eyelids. The orbicularis oculi muscle is innervated by the 7th cranial nerve, the facial nerve. There are two portions of the orbicularis muscle, the palpebral and the orbital. The palbebral portion of the muscle is used in the acts of blinking and voluntary winking. The eyelids are closed by the action of the orbicularis oculi muscle.
The superior oblique is innervated by the 4th cranial nerve, the trochlear nerve and is responsible for intorsion, depression, and abduction. The superior rectus is innervated by the superior division of the 3rd cranial nerve, the oculomotor nerve and
is responsible for elevation, intorsion, and adduction. The inferior oblique is also innervated by the oculomotor nerve and is responsible for extorsion, elevation, and abduction. The inferior rectus muscle is also innervated by the oculomotor nerve and
is responsible for depression, extorsion, and adduction (turning inward). The lateral rectus muscle is innervated by the 6th cranial nerve, the abducens nerve and is responsible for abduction (turning outward). The medial rectus muscle is innervated by the oculomotor nerve and is responsible for adduction or convergence. Extraocular muscle problems can contribute to strabismus, decreased depth perception and stereopsis, loss of fusion, loss of binocular vision, amblyopia, decreased visual acuity, ophthalmoplegias, eccentric fixation, diplopia, head tilting and head turning.
When myokymia occurs, it is believed that the focus of irritation is in the nerve fibers of the orbicularis muscle. Rarely, eyelid myokymia may occur with a hemifacial spasm, blepharospasm, Meige syndrome, and spastic-paretic facial contracture. Pontine dysfunction in the region of the facial nerve also has been implicated. Possible factors that can create eyelid myokymia include refraction problems, near point stress, accommodation and convergence difficulties, computer vision problems, nerve or muscle problems, general stress or anxiety, fatigue, overwork, sleep deprivation, excess caffeine use, nutritional imbalances, allergies, dry eyes, and alcohol use. It can also be seen in patients who have multiple sclerosis.
Myokymia also needs to be differentiated from ocular myopathy. Muscular dystrophies or ocular myopathies may affect the extraocular muscles and can produce ptosis and diplopia. Myasthenia gravis is a chronic neuromuscular transmitter disease characterized by fatigue of muscle groups. It usually starts with the extraocular muscles before the larger muscle groups become involved. Initial findings include ptosis which progressively becomes worse during the day. Weakness of convergence and upgaze are seen and paralysis of the inferior rectus or lateral rectus muscles can be seen.
Treatments for myokymia include drugs like dilantin, tegretol, neurontin, and botulinum toxin. Many people live with the condition. Patients need to be reassured that the condition will usually pass. Patients should be advised to reduce or eliminate the previously mentioned factors that can cause myokymia such as reducing caffeine use or by getting more sleep. Local subcutaneous botulinum toxin injections can provide relief over a time of 12-16 weeks. Alternative therapies include taking quinine sulfate tablets by prescription only at bedtime for one to two days. This should only be done under the care of a physician. Drinking quinine water may help but one needs to drink as much as two liters to get a beneficial dosage. Antihistamine drops can be effective and should be prescribed by an ophthalmologist or an optometrist. In very rare and complicated cases, eyelid surgery may be necessary.
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