Cranial nerve palsies that can affect the eye

 

• Fourth Cranial Nerve Palsy The double vision is vertical, that is, the two images are vertically misaligned and sometimes tilted. The causes of fourth cranial nerve palsy are many, but the two most common are head trauma and a vascular infarct, which is usually secondary to hypertension or diabetes. The diagnosis is confirmed by evaluating the patient's eye movements in all fields of gaze. The findings are often subtle, even to the ophthalmologist, but one eye is found to be slightly higher than the other and improves or worsens in specific head positions. If head trauma appears to be the cause of the nerve palsy, a CT scan of the brain may be in order if not already completed. In acquired cases in which diabetes or high blood pressure is present, a CT scan is usually not necessary unless other neurological abnormalities are present. In congenital fourth cranial nerve palsy, a CT scan of the brain may or may not be ordered depending on whether the child is symptomatic or other neurological findings are present. In acquired fourth cranial nerve palsy in which diabetes or high blood pressure is present, the prognosis is good for recovery of single vision. The process of resolution, however, may take 6 months or longer. During this period of time, prisms applied to glasses may be particularly helpful in restoring single vision, at least in straight-ahead gaze. The prisms are usually of the temporary type, being applied to the surface of the glasses, and perhaps, requiring different powers every few weeks as the condition resolves. Alternatively, in adults, a patch may be applied over one eye until resolution if the patient desires. If double vision persists beyond the sixth month following onset, strabismus surgery may be indicated in attempt to restore single vision. Young patients with congenital fourth nerve palsy must be observed for signs of amblyopia (lazy eye), though no other treatment is usually required.

• Sixth Cranial Nerve Palsy Sixth Cranial Nerve Palsy presents with horizontal double vision, that is, the two images are horizontally misaligned. Again, the double vision resolves when one eye is closed. In adults, the cause is usually a vascular infarct (diminished blood flow) of the nerve secondary to underlying diabetes or high blood pressure. Head trauma may also result in sixth cranial nerve palsy. In children, the condition usually follows a viral syndrome, though more serious intracranial inflammatory conditions and tumors must be considered. The diagnosis is usually easily confirmed by an ophthalmologist after observation of the eye movements in all fields of gaze. The affected eye will be unable to abduct (turn outwards beyond the midline). In adults with diabetes or high blood pressure and the sixth nerve palsy is the only other abnormal finding, a CT scan is usually not necessary. If there are any other concomitant neurological findings, pain, or a history of cancer, however, a CT scan will usually be obtained. In children, a CT scan is usually obtained to rule-out intracranial pathology. The prognosis for a full recovery in adults with diabetes or high blood pressure is good. However, recovery usually takes 3 to 6 months. Adults may elect to patch the eye to avoid double vision. In many cases, however, a temporary prism applied to the glasses may help restore single vision. The prism power may need changing every few weeks as the condition improves. For both children and adults in whom the condition fails to resolve, strabismus surgery may be considered.

• Third Cranial Nerve usually presents with sudden onset of double vision, which may be horizontal or vertical in character but disappears when one eye is closed. The eyelid is usually droopy and there may be significant pain. The cause of this condition is usually also related to diabetes or hypertension, though much more severe and potentially lethal disorders such as intracranial aneurysms may be present. The ophthalmologist will make the diagnosis based on the findings of an eye that moves outwardly but is otherwise largely immobile. Whether the pupil is involved (an afferent pupillary defect is present) will be heavily relied upon in the ophthalmologist's algorithm guiding the work-up. All patients who have an involved pupil will undergo neurological imaging (CT or MRI) while those in whom the pupil is spared (normal) may or may not undergo neuro-imaging, depending on many other factors, the scope of which is beyond this site. In patients with pupil-spared third cranial nerve palsies and underlying cardiovascular risk factors, such as diabetes and hypertension, there will likely be resolution of symptoms over 3 to 6 months. If not, an initial or repeat neuro-imaging study may be obtained. Because of the severe limitations of eye movement, prisms applied to the glasses may not be helpful in restoring single vision. However, the droopy eyelid that often accompanies this condition may act as occlusion, preventing double vision. Patients with pupil-involved third cranial nerve palsies will often be hospitalized while an intense evaluation is completed. Patients will be scheduled for a CT or MRI, "blood work," and perhaps cerebral angiography in young patients. Treatment of these patients depends on the myriad of potential causes for the third cranial nerve palsy.

• Fifth Cranial nerve palsy leads to loss of corneal sensation

• Seventh cranial nerve palsy can result in inabilty of the eyelids to close and can lead to exposure keratopathy