Bitemporal hemianopsia

Bitemporal hemianopia is the medical description of a type of partial blindness that is associated with lesions of the optic chiasm, the area where the optic nerves from the right and left eyes cross near the pituitary gland.

Causes
In bitemporal hemianopia vision is missing in the outer half of both the right and left visual fields. The temporal visual field information falls on nasal retina and the nasal visual field falls on temporal retina. The nasal retina is responsible for carrying the information from the temporal visual field, and it goes on to cross to the other side of the brain at the optic chiasm. When there is compression at optic chiasm the visual impulse from both nasal retina are affected, so it leads to inability to view the temporal, or peripheral, vision. This phenomenon is known as bitemporal hemianopia. Knowing the physiology of visual signal flow through the optic tract is very important in understandng bitemporal hemianopia.

Bitemporal hemianopia most commonly occurs as a result of tumors located at the mid-optic chiasm. Since the adjacent structure is the Pituitary gland, some common tumors causing compression are Pituitary adenomas, and Craniopharyngiomas.

Etymology
The absence of vision in half of a visual field is described as hemianopia.

The visual field of each eye can be divided in two vertically, with the outer half being described as temporal, and the inner half being described as nasal.

"Bitemporal hemianopia" can be broken down as follows:
 * bi-: involves both left and right visual fields
 * temporal: involves the temporal visual field
 * hemi-: involves half of each visual field
 * anopia: blindness