Visual Impairment in Alzheimer's Disease

Visual Impairment in Alzheimer's Disease

The documentation of a severe form of dementia by Alois Alzheimer in 1907 began a massive investigation of the cause of this disorder. Some of the common symptoms of Alzheimer's Disease consist of memory loss, impaired language ability, impaired judgement, and learning (M. Wong, et al. , 1997). Alzheimer's Disease (AD) is mainly a disease of the cerebral cortex. Alzheimer's is marked structurally by the senile plaques, neurofibrillary tangles, and severe loss of neurons and synapses in the cerebral cortex. Alzheimer's is a neurodegenerative disorder ( Hof, Vogt, Bouras, and Morrison 1997). Recent attention has been focused on visual dysfunction in Alzheimer's Disease (K. U. Loffler, D. P. Edward, & M. O. M. Tso 1995).

Visual Problems

During the clinical evaluation of patients with mild to moderate dementia of the AD type, visual difficulties such as : topographic agnosia, visual agnosia, alexia without agraphia, and prosopagnosia are detected. AD patients have The problem of describing the individual components of a picture is consistent with the severity of cytochrome oxidase (C.O.) deficits in the association cortical areas. Other deficits experienced by AD patients were texture discrimination, blue-violet discrimination, and 4.72 deg/sec motion detection. When AD patients were compared to other age-matched controls, AD patients had shown specific deficits in contrast sensitivity. Deficits in color vision were only age-related (M. Wong-Riley, et al. , 1997).

Studies

Selective degeneration of large ganglion cell axons was observed in the optic nerves of AD patients, which suggested an impairment of broad-band channel visual function. Although studies show that the broad-band visual capabilities are not selectively impaired in AD. Dorsal LGN studies have shown that both the magno- and parvicellular neurons were greatly affected in AD patients. Strangely, AD patients were impaired at low frequencies instead of the high frequencies, like in old age. This implies that regions controlling the low spacial frequency processing in the primary visual cortex would be affected more than those for high frequency processing (M. Wong-Riley, et al. , 1997). The neuropathologic examination of the brains with visual impairment in the Hof et al. (1997) study revealed cortical atrophy dominating on the posterior parietal cortex and occipital lobe(Hof et al.). A study by Beta-amyloid is considered an important factor in AD and was shown to be the major cause in senile plaques.

Acetylcholine

A number of neurotransmitters and neuromodulators, including acetylcholine (ACh), somatostatin and glutamate have been found to be deficient in Alzheimer's disease (AD).