The visual field includes central vision and peripheral (side) vision.
Ocular lesions may only cause visual field loss in one eye at a time (but may be in both eyes), and sometimes causes vision loss that splits the horizontal midline (because the blood supply to the retina has an upper and lower distribution).
In contrast brain lesions usually cause HEMIANOPSIA/HEMIANOPIA (blindness of a portion of the visual field respecting the vertical midline in both, or sometimes one eye). This is because the vision fibres from the left half of both eyes go to the right side of the brain, and the vision fibres from the right half of both eyes go to the left side of the brain. The vision fibres partially cross over in an area of the brain known as the optic chiasm.
The visual field can be tested with a perimeter (the round bowl machine with flashing lights at the front of our office).
Patients with pituitary tumors or craniopharyngiomas (less commonly meningiomas or aneurysms) may lose the side vision toward the ear side of both eyes, because the tumors can push on the area surrounding the chiasm. If medications or radiation shrink the tumour, or if the compressive lesion is removed from the chiasm, the field loss may recover. In patients with brain tumours, vision loss can sometimes occur as a long term side effect of radiation to the brain, especially in patients who also have required chemotherapy.
Patients with visual field loss from optic neuritis/multiple sclerosis may recover significant amounts of vision, but their problem may relapse.
If a patient has trauma, stroke or tumour of the optic nerve or brain, the field of vision usually does not recover completely. If the vision is not recovered by 12 months time, chances are it won’t. Patients with injury to the parietal lobe, especially the right side may also suffer from “neglect” which makes visual rehabilitation even more difficult.
In patients with hemianopsia it is usually very difficult to restore the side vision. An exception would be a surgical/medically treatable tumour that has not permanently damaged the vision fibres.
Vision “restitution” programs available (e.g. NovaVision acquired by Vycor, or VisioCoach Explorative Saccadic Training), but substantial recovery of peripheral vision is usually limited, and the programs can be expensive. “Adaptive” eye movements in to the blind field of vision, or improved motion perception, are more likely than actual return of the lost visual field. see J. Reinhard et al, Br J Ophthalmol 2005. L Henriksson et al, J Neurol Neurosurg Psychiatry 2007.
To increase peripheral awareness after loss of side vision from trauma or stroke, Dr. Ing has developed the free, but unvalidated EBI (Emend Brain Injury) slide program for patients.
Some patients with hemianopsia benefit from prisms. Examples of prisms include those by Gottlieb, and Peli.
A free website to help patients with stroke to read is at http://www.readright.ucl.ac.uk/