Each eye has a right and left visual field. These overlap the fields of the opposite eye. By looking in the eye, the physician may see swelling of the optic nerves. This may be an indication of increased intracranial pressure, caused by the growing tumor or obstruction of cerebral spinal fluid. This may cause slow and progressive visual loss involving both eyes.
Many children complain of blurred vision before the diagnosis of a brain tumor is made.
These changes cannot be corrected with glasses. One eye only is affected. This is because the pathways from each eye become crossed at this point. Patients with these problems usually find that half of their vision is missing to one side. When patients have difficulty behind the optic chiasm, the visual loss, because of the arrangement of the visual fibres, would be half or part of the vision on the one side so that the patient would have either the right side of the right eye vision lost and the right side of the left eye vision lost, or the reverse.