Bitemporal hemianopia

Bitemporal hemianopia is a specific type of visual disturbance in which sight in the outer half of the visual field of each eye is lost. As a result, the patient retains central vision but loses sight at the edges of his or her vision. This is not always obvious to him or her, even when the damage is quite severe on objective testing, because one tends to focus attention more on objects in the centre of the visual field.

Bitemporal hemianopia is usually caused by a lesion of the pituitary gland, most commonly a benign tumor pressing on the optic chiasm. Because it is the inner (medial) part of the retina which receives light from the outer visual field, this is what is lost when the inner part of the optic nerve is damaged by such a lesion.

Hemianopia signifies a loss of half of the visual field, and bitemporal denotes the two lateral, or temporal, sides of the head. By contrast, homonymous hemianopia signifies that the same half of each visual field is lost, ie all vision on the left, or on the right, of the midline. Such a pattern of visual loss is caused by damage to the more distal part of the optic radiation, most commonly by a stroke.