A type of strabismus where there is a vertical misalignment of the eyes is referred to as hypertropia.
Fourth nerve palsy is the most common cause of a vertical strabismus. Other causes can be: orbital trauma, thyroid related eye disease, or Brown's syndrome. Hypertropia has also been known to occur following glaucoma, cataract or retinal surgery and also may result following, or prior to, successful strabismus surgery for a horizontal eye misalignment.
About Fourth Nerve Palsy
Twelve cranial nerves, each with a specific function, begin in the brain's stem and lead to various parts of the head and neck. The fourth nerve delivers an impulse to a muscle on the eye's surface that is called the superior oblique muscle. This particular muscle moves the eye downward and, if it is weakened with a fourth nerve palsy, the eye tends to drift upwards in a vertical misalignment that is called hypertropia.
What are the Symptoms of Fourth Nerve Palsy?
Adults with fourth nerve palsy usually have double vision.
In both children and adults, a noticeable vertical deviation of the eyes is not always the first sign. Instead there is frequently a habitual head tilt to the side opposite the palsied eye. This head position, or torticollis, is compensation by the patient for the vertical strabismus. When the head is tilted, the vertical misalignment of the eyes is least pronounced. The tilting head enables the patient to achieve binocular vision and depth perception.
How is it treated?
Eye muscle treatment is the generally recommended treatment for fourth nerve palsy in children and adults. After surgery, the habitual head tilt usually disappears.
Before treatment the pediatric ophthalmologist must ensure there is no associated eye condition, such as amblyopia (decreased vision in one eye). This condition should be treated before eye muscle surgery is considered to correct the hyperopia.
Children with fourth nerve palsy cannot outgrow the disorder and it is important to contact a pediatric ophthalmologist if any of the above symptoms are noticed in your child.