Patients with small pituitary tumors do not typically develop visual symptoms. However, if a pituitary tumor has grown larger (usually more than 1 cm), then a patient can develop visual loss in one or both eyes. One pattern of visual loss that characteristically occurs is reduced peripheral vision to both sides. When these changes happen gradually, they can sometimes be difficult to notice.
Another important symptom that can occur with a pituitary tumor is double vision, where a person sees two images instead of one. This type of double vision exists when both eyes are open and goes away when either eye is closed.
The pituitary gland sits in a space called the pituitary sella, which is just a few centimeters behind the eyes. In order to see normally, we rely on our eyes to send information through cables (called the optic nerves) that travel back to the brain. A large pituitary tumor can push these cables, affecting their ability to send visual information from the eyes. Sometimes a pituitary tumor affects the optic nerve on just one side. In other cases, it affects a structure known as the “optic chiasm,” where the optic nerves from each eye merge together. When a pituitary tumor pushes the optic chiasm, it causes visual loss in both eyes.
In addition to the optic nerve, which brings vision from the eye to the brain, there are also several other nerves near the pituitary gland that travel to the eyes and help them move normally. If a pituitary tumor pushes one of these nerves, it causes weakness of some of the muscles that move the eye. This problem affects the normal alignment of the eyes, and produces double vision.
The doctor will perform a number of tests to check if a pituitary tumor is affecting vision. The examination will assess visual acuity, color vision, peripheral vision, eye movements, and the appearance of the retina and optic nerve (by looking at the back of the eye). To check peripheral vision, an automated test is commonly used, in which the patient pushes a button every time a flash of light is seen.
In many cases, surgery will be necessary to remove as much of the tumor as possible, especially where it is pushing on parts of the visual system (the optic nerves and optic chiasm). Some types of pituitary tumors can first be treated with medications that can shrink the tumor, and surgery may not be necessary. In some cases, radiation therapy can be used to treat the tumor.
Eyeglasses do not correct visual loss that occurs when a pituitary tumor has affected the optic nerves or optic chiasm. Eyeglasses are used to focus light in front of the eye. When the optic nerve or chiasm is injured, the problem causing loss of vision is behind the eye. If a patient has near-sightedness or far-sightedness as a separate problem, glasses can still be used for that reason.
Double vision that occurs with abnormal eye movements can be treated in several ways. One method is to block vision from one eye, so that the brain will no longer see two images. This can be done by wearing an eyepatch or by covering one eyeglass lens with scotch tape. In some cases, if the amount of misalignment of the eyes is very small, prisms can be placed in eyeglasses to shift images and reduce double vision. Finally, if double vision has become a permanent problem (without further improvement for about 12 months), then surgery can be performed to adjust the position of the eye muscles. The goal of this surgery is to reduce double vision when looking straight ahead and down, but double vision may still be present when looking to the sides.
In many cases, loss of vision can recover considerably after surgery or medical treatments. However, the extent of recovery depends on how long the visual loss has been present and how severe it is. Unfortunately, in some cases there is permanent visual loss, despite treatments for the pituitary tumor.
The frequency of eye examinations for a patient with a pituitary tumor will depend on the size of the tumor. It will also depend on whether visual symptoms have occurred, and whether medical or surgical treatments were necessary. Depending on these factors, some patients will need to have their vision checked periodically, often about every 6 to 12 months. Some patients will also need follow-up MRI scans to check for growth of the tumor.
If you notice a change in your vision, you should tell your doctor quickly. You may need a complete eye exam to determine the extent of any visual changes that could relate to the tumor. This will help determine what treatments will be necessary.
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