Dementia frequently impacts a person’s vision, though the cause is often misunderstood. The decline in mental ability does not typically involve damage to the physical structures of the eye itself. Instead, the primary challenge arises from the brain’s diminished capacity to correctly interpret the visual signals sent from otherwise healthy eyes. This decline in cognitive function fundamentally alters how a person perceives the world, making the distinction between an eye problem and a brain processing problem central to understanding these visual challenges.
Visual Processing: When the Brain Fails the Eyes
Vision involves the eyes capturing light and the brain interpreting the signals. In dementia-related vision impairment, the eyes may function well, but the cortical component—the brain’s visual processing centers—is failing. Neurodegeneration caused by conditions like Alzheimer’s disease and Lewy body dementia disrupts the pathways responsible for decoding visual input. This damage targets areas like the occipital lobe (basic visual processing) and the parietal and temporal lobes (spatial awareness and object recognition).
The deterioration of neurons means the brain struggles to organize raw data into a coherent image. Lewy body dementia, for example, is associated with severe visuospatial problems and visual hallucinations because the affected brain regions are involved in three-dimensional perception. Posterior Cortical Atrophy (PCA), often caused by Alzheimer’s pathology, begins in the rear regions of the brain, making visual processing deficits the earliest and most pronounced symptoms.
The brain’s failure to interpret signals results in a perceptual deficit: the person can see but cannot understand what they are seeing. Unlike standard age-related vision loss caused by cataracts or glaucoma, this neurological disruption cannot be corrected with traditional eyeglasses.
Specific Visual Perception Changes
Impaired Contrast Sensitivity
One common difficulty is impaired contrast sensitivity, the ability to distinguish an object from its background. The brain struggles to separate similar colors, causing surfaces to blend together visually. A person may struggle to see pale food on a white plate or a white toilet against a white-tiled floor. This impairment can lead to decreased appetite or an increased risk of falls.
Visuospatial Difficulties
Visuospatial difficulties cause a loss of depth perception and spatial awareness. Stairs or curbs may appear as a flat, confusing pattern, or a shiny floor may be mistaken for a wet surface. This often causes apprehension and refusal to walk forward. People may also misjudge distances, leading to errors when reaching for a cup or attempting to sit down.
Visual Agnosia
A person may experience visual agnosia, where they can clearly see an object but cannot recognize what it is or what it is used for. They might look directly at a telephone or a toothbrush and be unable to name it or recall its function, despite having sharp vision. This inability to identify familiar items or faces can be confusing and frustrating.
Misinterpreting Reflections and Patterns
Misinterpreting reflections and patterns is a frequent occurrence due to the brain mismanaging visual input. A person may become frightened by their own reflection in a mirror, believing it to be a stranger. They might also mistake a coat hung on a door for a person or an intruder. Busy patterns on wallpaper, carpets, or upholstery can be misinterpreted as actual objects, causing distress or visual hallucinations.
Strategies for Managing Vision Impairment
Addressing these vision changes requires modifying the environment to compensate for the brain’s processing difficulties, rather than just treating the eyes. One effective strategy is enhancing contrast to make objects stand out more clearly. For example, using high-contrast place settings, such as a dark-colored plate on a light tablecloth, helps the individual perceive the boundary of their meal.
In the bathroom, a brightly colored toilet seat placed on a white toilet can improve visibility and independence. Using a dark mat or tape on the edge of stairs can also help define the change in level that the brain struggles to process. Reducing visual clutter is beneficial, as complex patterns and numerous objects can create sensory overload and misperceptions.
Lighting adjustments are important, as people with dementia often have problems adapting to changes in light. Ensuring consistent, bright, non-glare lighting throughout the home can reduce harsh shadows that can be misinterpreted as obstacles. Minimizing reflections by covering large mirrors or using matte finishes on floors can prevent the confusion caused by misinterpreting reflections.
It is helpful to schedule regular eye examinations, but inform the optometrist that the person has dementia. Standard eye charts may not detect the cortical visual problems, so a specialized assessment is necessary to rule out treatable ocular conditions like cataracts. Caregivers should also be aware that a person’s visual field may narrow, making it necessary to approach and present objects directly in front of them to ensure they are seen.