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Individual differences |
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Biological: Behavioural genetics · Evolutionary psychology · Neuroanatomy · Neurochemistry · Neuroendocrinology · Neuroscience · Psychoneuroimmunology · Physiological Psychology · Psychopharmacology (Index, Outline)
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. Hemianopias occur because the right half of the brain has visual pathways for the left hemifield of both eyes, and the left half of the brain has visual pathways for the right hemifield of both eyes.
Homonymous hemianopsa can be congenital, but is usually caused by brain injury such as from stroke, trauma, tumors, infection, or following surgery.
Vascular and neoplastic (malignant or benign tumours) lesions from the optic tract, to visual cortex can cause a contralateral homonymous hemianopsia. Injury to the right side of the brain will affect the left visual fields of each eye. The more posterior the cerebral lesion, the more symmetric (congruous) the homonymous hemianopsia will be. For example, a person who has a lesion of the right optic tract will no longer see objects on his left side. Similarly, a person who has a stroke to the right occipital lobe will have the same visual field defect, usually more congruent between the two eyes, and there may be macular sparing. A stroke on the right side of the brain (especially parietal lobe), in addition to producing a homonymous hemianopsia, may also lead to the syndrome of hemispatial neglect.
Transient homonymous hemianopsia does not necessarily mean stroke. For instance, it can constitute the aura phase of migraine. Concomitant presence of a moving scintillating scotoma is suggestive of migraine, but has been seen in cerebral cancer as well.. Computed tomography (CT scan) or MRI can be used to investigate if stroke, tumor,structural lesion, or demyelination is the cause of homonymous hemianopsia.
Mobility can be difficult for people with homonymous hemianopia. “Patients frequently complain of bumping into obstacles on the side of the field loss, thereby bruising their arms and legs.”3
People with homonymous hemianopia often experience discomfort in crowds. “A patient with this condition may be unaware of what he or she cannot see and frequently bumps into walls, trips over objects or walks into people on the side where the visual field is missing.”5
Vision Restitution Therapy Edit
If hemianopsia has not improved by 6-12 months, it is unlikely to improve. The restoration of peripheral vision by "visual stimulation" is difficult. Many researchers feel that vision restitution therapy helps more with adaptive eye movements in to the blind hemifield, rather than restoration of the lost peripheral vision. Products such as Anops, NovaVision and VisioCoach are commercially available.
Help With Mobility Edit
Prisms or "field expanders" that bend light have been described for decades in patients with hemianopsia. Higher power Fresnel ("stick-on") prisms are commonly employed because they are thin and light weight, and can be cut and placed in different positions on a spectacle lens.
Peripheral prism spectacles expand the visual field of patients with hemifield visual defects and have the potential to improve visual function and mobility.4 Prism spectacles incorporate higher power prisms, with variable shapes and designs. The Gottlieb button prism, and the Peli superior and inferior horizontal bands are some proprietary examples of prism glasses. These high power prisms "create" artificial peripheral vision into the blind field for obstacle avoidance and motion detection.
Homonymous hemianopsia can be broken down as follows:
- Homonymous: (having the same name or designation) or standing in the same relation
- hemi: half
- anopsia: blindness
Homonymous hemianopsia is also called Homonymous hemianopia.
- ↑ Zhang X, Kedar S, Lynn MJ, Newman NJ, Biousse V (March 2006). Homonymous hemianopias: clinical-anatomic correlations in 904 cases. Neurology 66 (6): 906–10.
- ↑ 2.0 2.1 eMedicine > Posterior Cerebral Artery Stroke Authors: Christopher Luzzio and Consuelo T Lorenzo. Updated: Jul 15, 2009
- ↑ PMID 2958508 (PMID 2958508)
2 Schofield TM, Leff, AP, Rehabilitation of Hemianopia, Current Opinion in Neurology, 2009, 22:36-40
3 Peli E. Field expansion for homonymous hemianopia by optically induced peripheral exotropia. Optom Vis Sci 2000; 77:453-464.
4 Bowers AR, Keeney K, Peli E. Community-based trial of a peripheral prism visual field expansion device for hemianopia. Arch Ophthalmol 2008;126:657-664
5 Prism Glasses Expand The View For Patients With Hemianopia, Medical News today, 14 May 2008, www.medicalnewstoday.com/articles/107160.php
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