Bell Phenomenon: Function, Tasks, Role & Diseases

In Bell’s phenomenon, the eyeballs roll upward as they do during the eyelid closure reflex. The so-called faial nerve is primarily involved in the reflex movement, so failure to close the eyelids is often associated with facial nerve palsy. With incomplete eyelid closure, the white of the eyeball shows through the Bell phenomenon.

What is Bell’s phenomenon?

Bell phenomenon is characterized by an upward roll of the eyeballs. The Bell phenomenon is characterized by an upward roll of the eyeballs. This movement occurs as part of what is known as the eyelid closure reflex or blink reflex. This phenomenon is a reflexive protective movement of the eyes in which the eyelid closes automatically and involuntarily. As an innate foreign reflex, the efferent and afferent fibers of the eyelid closure reflex are not located in the same organ. Rather, eyelid closure is triggered by the interconnection of several successive synapses. The reflex movement induces eyelid closure following mechanical irritation of the cornea or skin in the immediate vicinity of the eye and is accompanied by upward rolling of the eyeballs. Bell’s phenomenon mainly refers to the visualization of this upward movement and thus of the white eyeball with reduced eyelid closure. In this form, the phenomenon has pathological value and occurs as a symptom mainly in the context of facial nerve paralysis. The eponym of the Bell phenomenon is the British physiologist Charles Bell, who first observed the phenomenon in the 19th century.

Function and task

The eyelid closure reflex is a physiological protective reflex designed to protect the human visual organ and cornea from mechanical injury, desiccation, and foreign bodies. The receptor of the reflex arc is the cornea. After stimulation of this reflector, the stimulus is transmitted in the form of an action potential to the trigeminal ganglion via the afferent limb and thus the nasociliary nerve and the first trigeminal branch of the ophthalmic nerve. Thus, excitation reaches the sensory fibers from which central ganglion cell processes extend to the nucleus of the trigeminal nerve. In the nucleus spinalis nervi trigemini, the stimulus is switched, travels via the superior colliculus into the formatio reticularis, and reaches the nucleus nervi facialis, where the efferent limb of the reflex movement begins. The fibers of the nucleus nervi facialis attach to the fibers of other facial nuclei and together with them form the facial nerve or VII cranial nerve. The visceromotor fibers of this facial nerve innervate the orbicularis oculi muscle. When excitation reaches this muscle, it contracts and elicits eyelid closure. The eyelid closure reflex is a consensual reflex with afferents on the ipsilateral and contralateral facial nuclei. Physiologically, the upward movement of the eyeballs occurs simultaneously with the reflex movement and has no disease value per se. Rather, the physiologic movement is itself a protective reflex and corresponds, for example, to the position of the eyeballs during sleep. However, if the movement is visible and thus the whiteness of the eyeballs becomes apparent during eyelid closure, then the Bell phenomenon may be considered pathologic. The eyelid closure reflex and eyeball rolling always occur simultaneously in both eyes. Activation of only one eye is not possible because of the circuitry. However, the Bell phenomenon can also be present in only one eye and thus occur, for example, in the context of unilateral facial paralysis that blocks eyelid closure in one of the two eyes.

Diseases and complaints

Facial nerve palsy is technically known as facial nerve palsy and corresponds to paralysis of the facial nerve. Facial nerve palsies can be congenital or acquired. They are caused by either peripheral or central nerve damage. Incomplete eyelid closure and thus the Bell phenomenon is characteristic of the pareses. Namely, while the eyelid closure reflex is absent, the Bell phenomenon persists even with lagophthalmos, or incomplete eyelid closure. Facial paresis may also be associated with drooping corners of the mouth. Attenuated or abolished frowning may also be symptomatic. A variety of causes are possible for incomplete eyelid closure due to facial nerve palsy. Infections such as Lyme disease can be the cause as well as head trauma, tumors or inflammations and strokes.Incomplete eyelid closure and Bell’s phenomenon are sometimes also associated with the expression of Bell’s palsy, in which there is unilateral facial nerve palsy. The cause of the paralysis is unknown in the case of Bell’s palsy. Presumably, the paresis is caused by compression of the facial nerve associated with inflammatory processes. In most cases, Bell’s palsy resolves on its own within a few weeks or passes with treatments with corticosteroids. Only rarely does it cause permanent damage. However, complete paralysis of one side of the face should be well treated to achieve healing with complete remission of symptoms. Both Bell’s phenomenon and Bell’s palsy are usually matters of neurology. Often, especially in cases of incomplete eyelid closure, these are symptomatic manifestations of a primary disease such as multiple sclerosis. This autoimmune disease causes episodic immunological inflammation in the central nervous system and thus demyelinates the central nervous tissue. The conductivity of the affected tissues is thus often permanently impaired. However, the Bell phenomenon and the eyelid closure reflex play a role for medicine not only in connection with diseases of the nervous system, but are also important parameters in anesthesia for estimating the depth of anesthesia.