Bitemporal hemianopsia, is the medical description of a type of partial

blindness Visual impairment, also known as vision impairment, is a medical definition primarily measured based on an individual's better eye visual acuity; in the absence of treatment such as correctable eyewear, assistive devices, and medical treatment� ...

where vision is missing in the outer half of both the right and left visual field. It is usually associated with lesions of the

optic chiasm In neuroanatomy, the optic chiasm, or optic chiasma (; , ), is the part of the brain where the optic nerves cross. It is located at the bottom of the brain immediately inferior to the hypothalamus. The optic chiasm is found in all vertebrat ...

, the area where the optic nerves from the right and left eyes cross near the

pituitary In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The hypoph ...

gland.

Causes

In bitemporal hemianopsia, vision is missing in the outer (temporal or lateral) half of both the right and left visual fields. Information from the temporal visual field falls on the nasal (medial) retina. The nasal retina is responsible for carrying the information along the

optic nerve In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived fro ...

, and crosses to the other side at the

. When there is compression at

, the visual impulse from both nasal retina are affected, leading to inability to view the temporal, or peripheral, vision. This phenomenon is known as bitemporal hemianopsia. Knowing the neurocircuitry of visual signal flow through the

optic tract In neuroanatomy, the optic tract () is a part of the visual system in the brain. It is a continuation of the optic nerve that relays information from the optic chiasm to the ipsilateral lateral geniculate nucleus (LGN), pretectal nuclei, and su ...

is very important in understanding bitemporal hemianopsia. Bitemporal hemianopsia 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 adenoma Pituitary adenomas are tumors that occur in the pituitary gland. Most pituitary tumors are benign, approximately 35% are invasive and just 0.1% to 0.2% are carcinomas.craniopharyngioma A craniopharyngioma is a rare type of brain tumor derived from pituitary gland embryonic tissue that occurs most commonly in children, but also affects adults. It may present at any age, even in the prenatal and neonatal periods, but peak incidence ...

s. Also, another relatively common neoplastic cause is

meningioma Meningioma, also known as meningeal tumor, is typically a slow-growing tumor that forms from the meninges, the membranous layers surrounding the brain and spinal cord. Symptoms depend on the location and occur as a result of the tumor pressing ...

s. A cause of vascular origin is an

aneurysm An aneurysm is an outward bulging, likened to a bubble or balloon, caused by a localized, abnormal, weak spot on a blood vessel wall. Aneurysms may be a result of a hereditary condition or an acquired disease. Aneurysms can also be a nidus ( ...

of the

anterior communicating artery In human anatomy, the anterior communicating artery is a blood vessel of the brain that connects the left and right anterior cerebral arteries. Anatomy The anterior communicating artery connects the two anterior cerebral arteries across the co ...

which arise superior to the chiasm, enlarge, and compress it from above.

Etymology

The absence of

vision Vision, Visions, or The Vision may refer to: Perception Optical perception * Visual perception, the sense of sight * Visual system, the physical mechanism of eyesight * Computer vision, a field dealing with how computers can be made to gain und ...

in half of a

visual field The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments". Or simply, visual field can be defined as the entire area that can be seen when an eye is fixed straight at a poin ...

is described as '' hemianopsia''. 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 hemianopsia" 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 * ''anopsia'': blindness (formed by ''a(n) ^no + opsis ^vision + ia'')

References

External links

{{DEFAULTSORT:Bitemporal Hemianopsia Blindness Visual disturbances and blindness

Causes

Etymology

See also

References

External links