The functions of the eye are influenced by impulses from several nerves in the skull called cranial nerves. The optic nerve translates visual information from the retina into nerve impulses that the brain can interpret. The oculomotor nerve controls motor impulses that allow the eye to move and track moving objects, as well as the ability of the pupil to dilate and constrict. Brain tumors can grow within these nerves or cause eye symptoms by growing in adjacent structures that compress the nerves or blood vessels that support them.
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Medline Plus lists bulging of one or both eyes as a symptom of optic glioma, a benign, slow-growing tumor of unknown origin that presses on the optic nerve. Its presence can cause increased pressure within the brain, which contributes to pushing the eye outward. Bulging of the eye is described by the medical term “proptosis.”
Altered Eye Movement
The Merck Manuals Online Medical Library explains that certain brain tumors can trap fluid within the brain and cause cavities, called ventricles, to enlarge. This condition, known as hydrocephalus, can result in difficulty when trying to move the eyes to look upward. Merck mentions tumors of the cerebellum, an area of the brain associated with balance, and the pineal gland, a gland in the brain that secretes melatonin, as causing this particular symptom.
The All About Vision website states that nystagmus is another possible consequence of brain tumors. Nystagmus is a condition wherein the individual experiences rapid, involuntary side-to-side eye movement.
Medline Plus warns that optic glioma can cause loss of vision in one or both eyes. This loss can affect the general vision, or in some cases may only affect peripheral vision. Tumors that affect vision can lead to complete blindness. Visual disturbances accompanied by headache are a sign that may be indicative of brain tumor.
Double vision is another eye symptom that may indicate the existence of a brain tumor. Choroid plexus papilloma, germinoma, pineal cell tumor and ependymoma are four different types of brain tumor that the neurosurgery department at Stanford School of Medicine lists as potential causes of double vision.