Bitemporal hemianopia

Loss of the temporal half of the visual field in both eyes, the half nearer each temple. It is also spelled bitemporal hemianopsia.

After a complete lesion of the center of the optic chiasm: bitemporal hemianopia. Fields as the patient sees them, central 30° with rings at 10° and 20°. Hatched areas are lost, and the dark ovals are the normal blind spots.

Lesion site: Optic chiasm, center
Left eye loses: Temporal half, 50% of the plotted field
Right eye loses: Temporal half, 50% of the plotted field
Pattern: Heteronymous: opposite halves in the two eyes, so the lesion is at the chiasm
Lost to both eyes at once: 0% of the central 30°
Fibers cut: 4 of the 8 fiber groups the model draws

Try in: Visual Field Defects Explorer →

Put the lesion at the center of the chiasm to see the crossing fibers of both eyes end at the midline.

What causes bitemporal hemianopia?

Damage to the fibers that cross at the center of the optic chiasm, most often from a pituitary adenoma pressing up from below. Those fibers come from the nasal half of each retina, which sees the temporal half of each eye’s field. Craniopharyngioma, meningioma and aneurysm are less common causes.

Why both temporal halves go

The lens inverts the image, so light from the temporal side of each eye’s field lands on the nasal half of its retina. At the chiasm those nasal fibers cross the midline, about 53 percent of each optic nerve in the counts of Kupfer, Chumbley and Downer, while the temporal fibers run past along the outer edges. A midline lesion catches only the crossers, from both eyes at once.

The two eyes lose opposite sides of the world, the left eye its left half and the right eye its right half, which makes the defect heteronymous: the pattern that places a lesion at the chiasm itself.

The fiber groups cut by a complete lesion of the center of the optic chiasm
Fibers from	See	Cross at the chiasm	Then run in
Left eye, nasal retina, upper half	Lower temporal quarter	Yes	Right optic tract, then the parietal radiation
Left eye, nasal retina, lower half	Upper temporal quarter	Yes	Right optic tract, then Meyer’s loop
Right eye, nasal retina, upper half	Lower temporal quarter	Yes	Left optic tract, then the parietal radiation
Right eye, nasal retina, lower half	Upper temporal quarter	Yes	Left optic tract, then Meyer’s loop

4 of the 8 fiber groups the model draws are cut; the other 4 reach the cortex.

How a pituitary tumor takes the field

A real tumor rarely cuts as cleanly as the drawing. A pituitary adenoma grows up out of the sella turcica and reaches the lower crossing fibers first. Those come from the lower retina and serve the upper field, so the loss usually begins in the upper temporal quadrants and spreads downward. A craniopharyngioma, pressing from above, tends to start in the lower temporal quadrants instead.

Why it can go unnoticed

Each eye keeps its nasal half, and in the central 30° the two nasal halves cover each other’s losses: the share of that field lost to both eyes at once is 0%. That is one reason a bitemporal hemianopia can go unnoticed until the eyes are tested one at a time. Each blind spot, 15° into the temporal field, now sits inside the defect.

Telling it apart

Bitemporal loss stops at the vertical meridian, the line through fixation where crossed and uncrossed fibers divide; the defects of eye disease, such as glaucoma, respect the horizontal meridian or no meridian at all. Its mirror image, the binasal hemianopia, comes from pressure on both outer edges of the chiasm, and pressure on one edge gives a nasal hemianopia in one eye.

Tools for the visual pathway

Visualiser · Biology Visual Field Defects Explorer Place a lesion anywhere from optic nerve to visual cortex and see each eye’s field loss, named and explained. Visualiser · Biology Blind Spot Mapper Watch a dot vanish, as Mariotte’s paper did in 1668, then map your own blind spot in degrees and see it as the optic disc on the retina. Visualiser · Biology Brain Explorer 101 brain structures, gyri to ventricles, separable.

Visual Field Defects Explorer puts a lesion anywhere on the pathway and draws every fiber it cuts.
Blind Spot Mapper maps your own blind spot, the dark oval in each chart, in degrees.
Brain Explorer has the optic nerves, chiasm, tracts and geniculate bodies as 3D models.

Sources: Kandel, Principles of Neural Science, 6th edition, chapter 22, for the pathway and its lesions; Purves, Neuroscience, 6th edition, chapter 12, for the pathway and its lesions; Kupfer, Chumbley and Downer, Journal of Anatomy 1967;101:393, for the 53 percent of optic nerve fibers that cross at the chiasm. A teaching diagram of complete lesions: real fields are read with the history, the other eye, the optic discs and imaging.