4th Nerve Palsy
A Few Facts About 4th Nerve Palsy
A little known or understood disorder, 4th Nerve palsy is an eye disorder in which the usual symptom is that of double vision. In this particular case, double vision means the image seen through one eye appears to be slightly above the image seen by the other eye. The exact cause of this disorder is not always known. In some instances it is known to be congenital, in other instances it is acquired, sometime after birth, and often as the result of an injury or the result of a systemic illness.
The Muscles And Eye Alignment - There are six muscles which control the movement of the eye. One of these, the superior oblique muscle, controls movement of the eye towards the nose. The muscle also plays a role in movement of the eye away from the nose as well as moving the eye in a downwards gazing direction. The muscle, and its corresponding movement are controlled from the brain which in turn receives impulses through what is called the 4th cranial nerve. When this nerve suffers from a disorder, such as palsy, the movement of the eye is affected. The eye's gaze will tend to drift upward and perhaps slightly inward. The upward drift of the eye's gaze is called hypertropia.
The muscles controlling eye movement are such that, under the direction of the nervous system and the brain, the two eyes are always in alignment. The effect of 4th nerve palsy is that the two eyes are no longer in alignment, and because of the upwards drift of one of the eyes, the image seen through that eye will be slightly lower than the image seen by the unaffected eye. In other words, there will be double vision.
Double Vision - The symptom, double vision, can be severe enough to require treatment, or may be barely noticeable. It is believed many more suffer from this disorder than has been documented, with the vast majority of these people being unaware of their condition. When the disorder is congenital, young children may not think of their double vision as being in anyway abnormal, unless the condition is severe. Very young children are not apt to complain of double vision, and it may be a few years before there is a realization that something is wrong. Young children will often subconsciously try to compensate for the condition by tilting the head slightly, which can be effective. For some individuals, especially adults, head tilt can result in neck pain and other problems, which may be the initial indication that something is wrong with the eyes. In some instances, head tilt can result in facial asymmetry, eye pain, and frequent headaches.
Treatment For 4th Nerve Palsy - When 4th nerve palsy does require treatment, such treatment may vary from prescribing special eyeglass prisms to surgery. Surgery usually involves repair of the eye muscles or adjusting the muscle attach points to put the eyes back in alignment. Muscles may even be cut to weaken them as a part of the alignment process. Surgical treatment is quite often successful, especially when the disorder is congenital. On the other hand, when the disorder is acquired, it is often said to be idiopathic, which means that the cause is not known. When this is the case, treatment can still be given, but the outcome or prognosis can remain in question for some time. A year may go by before it can be fully determined whether the treatment was successful or not. In cases where the condition is idiopathic, up to half of surgical treatments may be unsuccessful or only partially so. In some cases, although surgery hasn't completely fixed the problem, special prisms can sometimes make up the difference, although the use of prisms is best suited when only minor adjustments need to be made. In worst case situations, an affected person may have to wear an eye patch while driving or performing certain tasks for reasons of safety.