Hypertropia is a type of strabismus, or misalignment of the eyes. While some people have eyes that go inward (crossed eyes) or outward, hypertropia occurs when one eye turns upward. It may be constant or occur only when you’re tired or stressed.
Strabismus is usually diagnosed in children and affects about 2 percent out of every 100 children. Hypertropia is the least common form of strabismus. It’s estimated that about 1 child in 400 has hypertropia. The condition can also appear in adulthood, often as the result of disease or injury to the eye.
Children often don’t complain of symptoms. Besides the upward wandering of the eye, a parent may notice a child cocking his or her head to the side to try to bring the eyes into alignment and gain clearer vision.
Adults with the condition may notice the subconscious head tilt as well and also experience double vision. As with other types of strabismus, eye strain and headaches can occur.
Causes in children
There are several conditions that can cause hypertropia in children.
Fourth cranial nerve palsy
The most common cause of hypertropia in children is fourth cranial nerve palsy. The fourth cranial nerve travels from the brain stem to a muscle on the surface of the eye, called the superior oblique muscle. The nerve sends impulses to the muscle, which controls the downward movement of the eye.
When the fourth cranial nerve is paralyzed (palsy) or weakened, it can’t control the superior oblique muscle correctly. This causes the eye to tilt upward.
A child may be born with a weakened or paralyzed fourth cranial nerve or develop it after a head trauma, such as a concussion.
Brown syndrome is a condition that causes a tight superior oblique tendon. That, in turn, restricts the eye’s movement. Doctors aren’t sure what causes the syndrome, but it’s commonly seen at birth.
It’s also possible to acquire Brown syndrome following an injury to the eye socket, such as being hit by a hard object, or by dental or sinus surgery.
This is another strabismus problem that people can be born with. For reasons that aren’t entirely clear, one of the cranial nerves may not develop normally. That restricts movement of the eye muscle.
Causes in adults
Causes in adults are different from the causes when first seen in childhood.
A neurological event, like a stroke, is the most common reason adults experience a turning of the eye, such as hypertropia. A blood clot that leads to a stroke can also damage the nerves that help control the movement of the eyes. According to the National Stroke Association, two thirds of people who experience a stroke encounter vision changes afterward.
Graves’ disease is an autoimmune disease that targets the thyroid gland. An autoimmune disease is a disease in which your body’s immune system fights against healthy cells.
The damage to the thyroid gland can affect eye muscles, causing them to work improperly.
Injury to the bones of the eye socket can lead to a strabismus like hypertropia. Surgery to repair cataracts can also cause this condition although it isn’t common for this to happen.
A brain tumor can press on the nerves and muscles of the eye, causing the eyes to move out of alignment.
Hypertropia is best treated by an eye doctor, an ophthalmologist, or an optometrist.
Your doctor may ask about your family’s medical history and whether you’ve had any trauma to the eye. They’ll then perform various eye tests. For example, you may be asked to read from an eye chart, or the doctor may shine a light into your pupils to see how they reflect light.
If your doctor suspects something like a brain tumor they’ll order imaging tests, like a CT scan or MRI, to visualize internal organs.
One of the major complications of hypertropia in children is amblyopia, or lazy eye. When eyes are misaligned, the brain gets two different visual cues. One cue comes from the straight eye and one cue comes from the eye facing upward. The brain will tend to shut off the signal from the misaligned eye and focus on messages sent from the straight, or “good” eye. As such, the weaker eye becomes even weaker and the stronger eye gets stronger. The end result is unbalanced vision.
Unbalanced vision can also affect depth perception, or what’s referred to as 3-D vision. The earlier a lazy eye is detected and treated, the better. If it isn’t corrected by the time vision matures, usually around the age of 8, lazy eye can be much harder to improve.
Your child won’t outgrow hypertropia and the condition won’t get better on its own. There are three main treatments for hypertropia. Your doctor may suggest one or all of them:
- Glasses. Lenses that correct any near- or farsightedness can help improve misalignment of the eyes. Also, prism can be added to glasses to help with alignment of the eyes.
- Patching. Muscles, including the muscles of the eye, get stronger when they’re regularly worked. Placing a patch over the strong eye for a prescribed number of hours a day will encourage the wearer to use the weaker eye, thereby strengthening it and possibly improving vision.
- Surgery. A trained surgeon can strengthen weak eye muscles and loosen tight ones to bring the eyes into alignment. Sometimes there might be overcorrection, however, and surgeries may need to be repeated.
While hypertropia may be the least common form of strabismus, misalignment of the eyes affects millions of people. When caught and treated early, complications can be avoided and eyesight can be saved and even strengthened.