Binasal hemianopsia is the medical description of a type of partial blindness

Blindness

Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...

 where vision is missing in the inner half of both the right and left visual field. It is associated with certain lesions of the eye and of the central nervous system

Central nervous system

The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

, such as congenital hydrocephalus

Hydrocephalus

Hydrocephalus , also known as "water in the brain," is a medical condition in which there is an abnormal accumulation of cerebrospinal fluid in the ventricles, or cavities, of the brain. This may cause increased intracranial pressure inside the skull and progressive enlargement of the head,...

.

Etymology

The absence of vision

Visual perception

Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...

 in half of a visual field

Visual field

The term visual field is sometimes used as a synonym to field of view, though they do not designate the same thing. The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments", while 'field of view' "refers to the physical...

 is described as hemianopsia

Hemianopsia

Hemianopia, or hemianopsia, is a type of anopsia where the decreased vision or blindness takes place in half the visual field of one or both eyes. In most cases, the visual field loss respects the vertical midline...

.

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.

"Binasal hemianopsia" can be broken down as follows:

• bi-: involves both left and right visual fields
• nasal: involves the nasal visual field
• temporal: involves the temporal visual field
• lateral: involves the lateral visual field
• hemi-: involves half of each visual field
• anopsia
  Anopsia
  An anopsia is a defect in the visual field. If the defect is only partial, then the portion of the field with the defect can be used to isolate a lesion.Types of partial anopsia:*Hemianopsia**Homonymous hemianopsia...
  
  : blindness

Causes

In binasal hemianopsia, vision is missing in the inner (nasal or medial) half of both the right and left visual fields. Information from the nasal visual field falls on the temporal (lateral) retina. Those lateral retinal nerve fibers do not cross in the optic chiasm. Calcification of the internal carotid arteries can impinge the uncrossed, lateral retinal fibers leading to loss of vision in the nasal field.

Note: Clinical testing of visual fields (by confrontation) can produce false positive result (particularly in inferior nasal quadrants).