Several nerves can be paralyzed, affecting eye movement and function. The specific nerve depends on the symptoms and the affected muscle.
Common Nerves Involved in Eye Paralysis:
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Abducens Nerve (Sixth Cranial Nerve): This is the most common nerve affected in adult ocular motor paralysis and the second most common in children. The abducens nerve controls the lateral rectus muscle, responsible for moving the eye outward (abduction). Paralysis of this nerve results in an inability to turn the affected eye outward, leading to esotropia (inward turning of the eye) due to the unopposed action of the medial rectus muscle. [Source: Abducens (sixth cranial) nerve palsy is the most common ocular motor paralysis in adults and the second-most common in children. The abducens nerve controls the lateral rectus muscle, which abducts the eye. Abducens nerve palsy causes an esotropia due to the unopposed action of the antagonistic medial rectus muscle.]
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Trochlear Nerve (Fourth Cranial Nerve): Paralysis of this nerve affects the superior oblique muscle, causing double vision (diplopia) when both eyes are open. Closing one eye eliminates the double vision. [Source: Double vision (diplopia) is a common symptom of fourth nerve palsy. It occurs only when both eyes are open. With one eye shut, you see one image.]
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Oculomotor Nerve (Third Cranial Nerve): Paralysis of this nerve results in a variety of symptoms depending on which muscle fibers are affected. It controls most of the eye muscles and the pupil's size. [Source: Examining the function of the superior oblique muscle in the presence of total third nerve paralysis. When the third cranial nerve is paralyzed, the eye...] A complete paralysis would affect eye movement in various directions and pupil dilation.
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Facial Nerve (Seventh Cranial Nerve): While not directly controlling eye movement, facial nerve paralysis (like in Ramsay Hunt syndrome) can affect the muscles around the eye, making it difficult or impossible to close the eyelid. This can lead to dry eye and other complications. [Source: Patients may have difficulties or find it impossible to close the eye due to paralysis of the orbicularis oculi muscle that surrounds the eye. A shingles outbreak can affect the facial nerve near one of your ears, potentially causing facial paralysis and hearing loss ... This damage can cause eye pain… ]
Microvascular Cranial Nerve Palsy:
This condition involves a blockage of blood flow to cranial nerves, which can include those controlling eye movement. [Source: Microvascular cranial nerve palsy (MCNP) is when blood flow to certain nerves in your head (called cranial nerves) is blocked.]
