Visual system manifestations of Alzheimer's disease

Alzheimer's disease (AD) is an increasingly common disease with massive personal and economic costs. While it has long been known that AD impacts the visual system, there has recently been an increased focus on understanding both pathophysiological mechanisms that may be shared between the eye and brain and how related biomarkers could be useful for AD diagnosis. Here, were review pertinent cellular and molecular mechanisms of AD pathophysiology, the presence of AD pathology in the visual system, associated functional changes, and potential development of diagnostic tools based on the visual system. Additionally, we discuss links between AD and visual disorders, including possible pathophysiological mechanisms and their relevance for improving our understanding of AD.     

Visual symptoms as the first manifestation of Alzheimer's disease

CASE REPORT: We report a 59-year-old patient with difficulty in visual perception, difficulty reading and episodes of dyschromatopsia. The ocular examination was unremarkable. Structural neuro-imaging and neuro-ophthalmology tests were normal. Positron emission tomography scanning showed decreased metabolism in the parieto-occipital cortex bilaterally. Several months later the patient developed Alzheimer's disease. DISCUSSION: Visual symptoms may be the first manifestation of Alzheimer's disease.     

Disorders of the visual system in Alzheimer's disease

Alzheimer's disease (AD) is associated with disturbances in basic visual, complex visual, and oculomotor functions. The broad range of visual system disorders in AD may result from the concentration of neuropathology in visual association cortex and optic nerves in this disease. AD patients and their caregivers frequently report visuospatial difficulties in these patients. Examination of the visual system in AD may reveal visual field deficits, prolonged visual evoked potentials, depressed contrast sensitivities, and abnormal eye movement recordings. Complex visual disturbances include constructional and visuoperceptual abnormalities, spatial agnosia and Balint's syndrome, environmental disorientation, visual agnosia, facial identification problems, and visual hallucinations. The purpose of this article is to review the spectrum of visual system disturbances found in AD and, in particular, to describe the methods used to screen for complex visual abnormalities in these patients.     

Visual acuity of the preschool child: a review

The need for visual acuity assessment in preschool children has long been recognized, yet there are no standardized visual acuity norms or screening criteria. This report reviews the literature on distance visual acuity in the preschool child. The areas of review include: methods of assessment of visual acuity; visual acuity norms obtained with these tests; reasons for the variations in reported visual acuity norms; variations in referral criteria for vision screenings; testability reported for various visual acuity tests; and important design principles and recommendations for preschool visual acuity tests. It is concluded that a well designed preschool visual acuity test should consist of high contrast Snellen optotypes without directional components that progress in 0.1 log steps down to a level of 6/3. To improve testability, a matching or forced choice response should be used. Of the tests that have been standardized, STY-CAR (Sheridan-Gardiner) comes closest to meeting these criteria.     

Ophthalmologic manifestations of Alzheimer's disease

Alzheimer's disease is a progressive neurologic disorder which may present with visual disturbance before the diagnosis is clearly established. Central acuity and visual field are initially normal. Alzheimer patients may show anomalies of color vision, spatial contrast sensitivity, susceptibility to visual masks, fundus examination, ocular motility, higher cortical visual function, visual evoked potential, and pattern electroretinogram. Pathologic analysis has shown abnormalities at all levels of the visual axis from retinal ganglion cell to associative visual cortex. Correlations between the visual abnormalities of Alzheimer's disease and corresponding neuroanatomic substrates are discussed.     

Alzheimer病与视网膜变性

Alzheimer病(Alzheimer's disease,AD)是一种进行性神经变性疾病,它是导致老年痴呆的主要原因且至今无法治愈.β淀粉样蛋白斑块沉积和tau蛋白引起的神经纤维缠结是导致AD患者大脑病变的两大主要机制.近来发现越来越多的AD患者除了意识和行为障碍,还存在眼部症状.有研究表明AD相关的β淀粉样蛋白斑块不仅沉积于大脑,同时累及视网膜,且视网膜病变较大脑病变更易观察诊断.因此,研究AD相关的视网膜变性不仅有助于深入了解脑部病变过程,为AD提供一种全新的简单有效的诊疗方法,也有益于研究如青光眼和年龄相关性黄斑变性等其他视网膜变性类疾病的病理机制.     

Ocular changes in Alzheimer's disease

PURPOSE: In this study the authors present the ocular diseases and bioelectrical dysfunction of the retina and optic nerve in patients with Alzheimer's disease, based on available literature. MATERIALS AND METHODS: The paper focuses on the most often occurring ocular diseases and optic nerve dysfunction associated with Alzheimer's disease measured by ERG, PERG and VEP tests. RESULTS: The most common ocular diseases in Alzheimer's disease are glaucoma, cataract and AMD. Electrophysiological tests can be abnormal in patients with Alzheimer's disease even with normal eye fundus in routine ophthalmic examination. CONCLUSIONS: Early diagnosis of ocular changes associated with Alzheimer's disease can prevent from significant loss of vision and can prolong self-reliant existence of patients with this disease. Electrophysiological tests are expected to be helpful in differentiation between patients with early stages of Alzheimer's disease and healthy people or people suffering from other types of dementia or mental diseases. Future research to estimate the diagnostic value of this tests are needed.     

Ophthalmological aspects of Alzheimer's disease

Patients with Alzheimer's disease may present to the ophthalmologist with visual symptoms that precede or overshadow the features of dementia. This visual variant of Alzheimer's disease has been recognized only recently and typically appears in late middle age as progressive visuospatial and reading dysfunction, with normal visual acuity and fields. Common features include simultanagnosia and the other features of Balint's syndrome, and variable hemispatial neglect and hemianopia. The neuroimaging and neuropathological findings in this Alzheimer's variant are distinct and suggest disruption of occipitoparietal visual projections. The identification of the visually symptomatic patient who is destined to develop other signs of Alzheimer's disease depends on the use of appropriate screening tests, including text reading, figure-ground discrimination, and other bedside tests of visuospatial attention and perception.     

Visual function in autism spectrum disorders: a critical review

Studies have shown considerable evidence of visual dysfunction in autism spectrum disorders. Anomalies in visual information processing can have a major effect on the life quality of individuals with autism spectrum disorders. We summarise the hypotheses and theories underlying neural aetiologies and genetic factors that cause these disorders, as well as the possible influences of unusual sensory processing on the communications and behaviour characterised by the autistics. In particular, we review the impact of these dysfunctions on visual performance.     

Visual prognosis of coats'' disease

PURPOSE: Our purpose was to determine the visual prognosis of retinal telangiectasia (Coats' disease). METHODS: We performed a retrospective review of 35 patients with Coats' disease seen at the Hospital for Sick Children, Toronto, Canada between 1987 and 1996. Ten patients were excluded because of incomplete records. Treatment modalities consisted of no treatment, cryotherapy with and without 532 nm laser through the indirect ophthalmoscope, and enucleation. Visual outcome was determined where possible. RESULTS: Median follow-up was 4.5 years. Deterioration in visual acuity was associated with the presence of greater than 5 clock hours of involved retina and retinal detachment at diagnosis. Final visual acuity did not correlate with age of onset of disease. No eye treated with cryotherapy progressed to retinal detachment. CONCLUSIONS: Aggressive treatment of Coats' disease with cryotherapy with or without 532 nm laser, before retinal detachment, is likely to stabilize vision and decrease the risk of future total retinal detachment.     

Stargardt病的视觉电生理表现

对22例（44眼）stargardt病进行F－ERG、EOG检查，患者年龄8～44岁，平均22．4岁；男性12例，女性10例；矫正视力在0．04～0．5之间，90％眼视力在0．1～0．2之间。F－ERG结果显示明、暗视系a波损害明显大于b波损害；EOG结果显示异常率达80％。眼电生理学检查支持本病的主要病变位于视网膜色素上皮－光感受器复合体。     

Retinal abnormalities in early Alzheimer's disease

PURPOSE: There is evidence suggesting that visual disturbances in patients with Alzheimer's Disease (AD) are due to pathologic changes in the retina and optic nerve, as well as to higher cortical impairment. The purpose of this study was to evaluate retinal hemodynamic parameters and to characterize patterns of retinal nerve fiber layer (RNFL) loss in patients with early AD. METHODS: Nine patients with mild to moderate probable AD (mean Mini Mental State Examination score 24 of a possible 30 (age 74.3 +/- 3.3 years; mean +/- SD) and eight age-matched control subjects (age, 74.3 +/- 5.8 years) were included in this prospective cross-sectional study. Blood column diameter, blood velocity, and blood flow rate were measured in the major superior temporal retinal vein in each subject by using a laser Doppler instrument. Peripapillary RNFL was measured by optical coherence tomography. RESULTS: Patients with AD showed a significant narrowing of the venous blood column diameter (131.7 +/- 10.8 microm) compared with control subjects (148.3 +/- 12.7 microm, P = 0.01), and a significantly reduced venous blood flow rate (9.7 +/- 3.1 microL/min) compared with the control subjects (15.9 +/- 3.7 microL/min, P = 0.002). A significant thinning of the RNFL was found in the superior quadrant in patients with AD (92.2 +/- 21.6 microm) compared with control subjects (113.6 +/- 10.7 microm, P = 0.02). There were no significant differences in the inferior, temporal, or nasal RNFL thicknesses between the groups. CONCLUSIONS: Retinal abnormalities in early AD include a specific pattern of RNFL loss, narrow veins, and decreased retinal blood flow in these veins. The results show that AD produces quantifiable abnormalities in the retina.