Hemianopsia
Encyclopedia
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 most common causes of this damage include stroke, brain tumor and trauma.
The word Hemianopsia is from Greek origins, where:
A homonymous hemianopsia
is the loss of half of the visual field on the same side in both eyes. The visual images that we see to the right side travel from both eyes to the left side of the brain, while the visual images we see to the left side in each eye travel to the right side of the brain. Therefore, damage to the right side of the posterior portion of the brain or right optic tract can cause a loss of the left field of view in both eyes. Likewise, damage to the left posterior brain or left optic radiation can cause a loss of the right field of vision.
A Heteronymous hemianopsia is the loss of half of the visual field
on different sides in both eyes. It is separated into two categories:
Quadrantanopia (quadrantanopsia/quadrantic hemianopia) is decreased vision or blindness in one quarter of the visual field. The particular quarter of vision missing depends on whether the location of the brain damage is temporal or parietal. For example, a lesion to the right temporal lobe with damage specifically to Meyer's loop will give rise to a left upper quadrantanopsia, while a lesion to the right parietal radiation will result in a left lower quadrantanopsia.
are able to partially compensate hemianopsia, by distorting the vision field.
As a component of Vision Rehabilitation, NovaVision Vision Restoration Therapy (VRT™) is a non-invasive program intended to improve the visual field with light stimulation in patients with impaired vision due to stroke, trauma, or other acquired brain inuries.
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...
where the decreased vision or blindness takes place in half the 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...
of one or both eyes. In most cases, the visual field loss respects the vertical midline. The most common causes of this damage include stroke, brain tumor and trauma.
Etymology
- "Hemi" means "half",
- "an" means "without",
- "opsia" means "seeing".
Types of hemianopsia
When the pathology involves both eyes, it is either Homonymous or Heteronymous.Homonymous hemianopsia
Homonymous hemianopsia
Hemianopsia or hemianopia is visual field loss that respects the vertical midline, and usually affects both eyes, but can involve one eye only. Homonymous hemianopsia, or homonymous hemianopia occurs when there is hemianopic visual field loss on the same side of both eyes...
is the loss of half of the visual field on the same side in both eyes. The visual images that we see to the right side travel from both eyes to the left side of the brain, while the visual images we see to the left side in each eye travel to the right side of the brain. Therefore, damage to the right side of the posterior portion of the brain or right optic tract can cause a loss of the left field of view in both eyes. Likewise, damage to the left posterior brain or left optic radiation can cause a loss of the right field of vision.
Heteronymous hemianopsia
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...
on different sides in both eyes. It is separated into two categories:
- Binasal hemianopsiaBinasal hemianopsiathumb|Paris as seen with full visual fieldsthumb|Binasal hemianopsia is the medical description of a type of partial blindness where vision is missing in the inner half of both the right and left visual field...
- The loss of the fields surrounding the nose; - Bitemporal hemianopsiaBitemporal hemianopsiaBitemporal hemianopsia is the medical description of a type of partial blindness where vision is missing in the outer half of both the right and left visual field...
- The loss of the fields closest to the temples.
Other forms
- Superior hemianopia: the upper half of the field of vision is affected;
- Inferior hemianopia: the lower half of the field of vision is affected.
Quadrantanopia
Treatment
New research in hemianopia and quadrantanopia rehabilitation has led to improved treatment options. For instance, several types of lensLens (optics)
A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...
are able to partially compensate hemianopsia, by distorting the vision field.
As a component of Vision Rehabilitation, NovaVision Vision Restoration Therapy (VRT™) is a non-invasive program intended to improve the visual field with light stimulation in patients with impaired vision due to stroke, trauma, or other acquired brain inuries.