What is Lateral Rectus Muscle Palsy (LR Palsy)?

Lateral Rectus Muscle Palsy, also called Lateral Rectus Palsy and LR Palsy is a condition of the Lateral Rectus Muscle of the eye that is caused by a problem with the sixth cranial nerve. To better understand Lateral Rectus Muscle Palsy, this article will discuss the LR muscle and the other muscles of the eye and how they work. Some of the medical/ocular terminology will be discussed below.

Medical terms are often difficult to understand until one learns something about the associated organs. The eye may appear (to some people) a relatively simple organ for seeing, but it is very complex. There are lots of muscles, nerves and blood vessels that keep the eye functional and healthy. Of the many muscles that surround the eye, there are six extraocular muscles which are relatively small in size, but are very strong and efficient. These muscles are help the eyes to move up and down; they also help the eyes rotate, fix on whatever person or object the person focuses on.

The muscles of the eye

The six extraocular muscles are called the Medial Rectus (MR), Lateral Rectus (LR), Superior Rectus (SR), Superior Oblique (SO) and the Inferior Oblique (IO). The primary muscle in each of the eyes that help the eyes move in the same direction is called an agonist muscle. The other muscle in each of the eyes that help the agonist muscles to move the eyes in the same direction is called synergist muscle. The muscles in each of the eyes that allow the eyes to move in the opposite direction are called an antagonist muscles. Of the six extraocular muscles, the Lateral Rectus muscle helps to move the eye outward, away from the nose is called an abduction muscle. (This may sound confusing, but if you move your eyes in the line of your finger toward your nose and to follow the movement of your finger to the right and to the left, you will understand how the agonist, antagonist, antagonist and abduction muscles work.)

Causes for Lateral Rectus Muscle Palsy

For these muscles to create their intended eye movements, the muscles are connected to the brain through nerves. The Lateral Rectus muscle is innervated by the sixth cranial nerve, also known as the Abducens Nerve. When the sixth cranial nerve, along with its course and nucleus in the pons get injured for various reasons, it results in a disorder of the muscle that the nerve that innervates the muscle. The condition is called Lateral Rectus Muscle Palsy. This dysfunction of the sixth abductor nerve causes Lateral Rectus Muscle weakness that leads to a condition called Horizontal Diplopia, which is the term to indicate double vision. There could be many other conditions associated with the sixth cranial nerve injury including hypertension, craniocerebral trauma (head injury), ischemia (low blood flow) and neoplasm (tumor or new growth of tissue). Though, incidences are rare, Lateral Rectus Palsy could be an early sign of Multiple Sclerosis. There may also be facial numbness with LR Palsy, and numbness can occur with other cranial nerve disorders.

Lateral Rectus Palsy is usually an acquired condition, which can be due to a lesion or stroke caused by hypertension or some other traumatic event. It is possible, but very rare that LR Palsy would be congenital (occurring at birth). LR Palsy causes the eyes to be misaligned, which results in distorted vision.

Symptoms of Lateral Rectus Muscle Palsy

Distorted vision may be the primary symptom that aids the medical professional to make a definitive diagnosis. If an individual has Lateral Rectus Muscle Palsy, the affected eye cannot be rotated away from the midline due to muscle weakness. When both eyes are examined, the diseased eye will appear turned away while the normal eye is fixed in place, when looking straight ahead.

Treatment for Lateral Rectus Muscle Palsy

An individual affected by paralysis of the LR muscle will likely turn his/her face and head toward the side of the diseased eye; this is done to compensate for the double vision error. Usually LR Palsy will resolve with rest and the elimination of the underlying cause. However, if permanent damage is done to the Lateral Rectus Muscle, the error in vision could be corrected by using a prismatic lens that can be fixed into one's eyeglasses. The prismatic lens corrects double vision by projecting a single image to the retina, which is thereby interpreted by the brain.

Conclusion

In the "olden days" people used to cover the diseased eye with a dark eye patch to block the vision in the affected eye. Now, modern surgery techniques have evolved to set the diseased nerves and muscles in correct alignment. Surgery is an option for people who have had LR muscle paralysis for a long time. The doctor will advise the patient to wait for a period of time to see if the paralysis will resolve on its own.

Sources:

Eye Movements

Sixth Cranial Nerve Palsy (LR Palsy)