How Alzheimer’s Disease Affects Vision and Perception

by Audrey Demmitt, RN and VisionAware Peer Advisor

People with dementia can have difficulties with vision and perception which causes them to misinterpret the world. The process of seeing is complicated and there are many points where things can go wrong. Disturbances in vision and perception can cause behavioral challenges and even safety risks. Caregivers who understand this will be better able to support their loved one and modify their physical environment, so they can remain at home longer.

The Eyes and Brain Work Together

Diagram: Visual Pathway. The diagram uses a picture of a tree to illustrate how the image falls to the back of the retina (upside down image), with the signal from each eye traveling along the Optic Nerve to the Optic Chiasm. At the Chiasm the right visual fields (temporal of right eye and nasal of left) travel down the Optic tract to the right side of the brain and the left visual fields of each eye (temporal of left and nasal of the right eye) travel the optic tract to the left side of the brain. The signals together are interpreted at the Visual cortex of the Occipital lobe.

 

Because Alzheimer’s is a disease of the brain and many seniors also have vision changes and age-related eye conditions like cataracts and macular degeneration, various kinds of visual mistakes can occur. Let’s consider the basics of the visual process. First, information is transmitted from your eyes to your brain where it is then interpreted. Your other senses, thoughts and memories contribute information that influences your interpretation. Next, you become aware of what you have seen, forming a perception. These visuoperceptions can be inaccurate or faulty depending on the function of the eyes and the area of the brain that is diseased, causing distress for the affected person as well as their caregivers.

Common Visual Deficits

In Alzheimer’s dementia, there are five main areas of visual deficit that can cause mistakes in perceptions: motion detection, peripheral vision, depth perception, color perception, and contrast sensitivity.

Reduced ability to detect motion. Some people are unable to detect movement. They perceive the world as a series of still photos, rather than an ongoing video like most people see. This view of the world can cause affected persons to become lost, even in familiar surroundings. Following a moving object can be difficult and impacts the ability to comfortably watch television or do any activity involving fast motion.

Depth perception. Individuals with Alzheimer’s can lose their depth perception. They have a hard time judging distances, changes in elevations or distinguishing between a three-dimensional object and a flat picture. They may reach to pick up the flowers on a floral fabric or step up when they come to a border on a carpet as if it were a step.

Reduced peripheral vision. People’s field of vision narrows as they age; but for some with Alzheimer’s disease, it narrows dramatically. They may be unable to see to either side when gazing forward, resulting in disorientation and a tendency to bump into things. They may be startled by someone approaching them or need to suddenly veer to miss a wall.

Color perception.Though colors often diminish with age, persons with Alzheimer’s seem to have a greater deficit and will have difficulty recognizing colors, especially in the blue-violet range. Coordinating clothing may be a problem.

Contrast sensitivity. Not just color, but detecting gradients of color also is reduced in persons with Alzheimer’s. They will have trouble picking out objects that are surrounded by similar colors. For example, a person may have difficulty finding the toilet in a bathroom where the floor, walls and toilet are all white.

Problems with Object and Facial Recognition

Alzheimer’s dementia can cause problems with the recognition of objects and faces causing an inability to name what is seen.

Common Visual Perception Mistakes

  • Illusions – when a person sees a "distortion of reality." This may result from a characteristic of the object. A shiny floor may be perceived as wet or a face may appear in a patterned curtain.
  • Misperceptions – what the person sees is a ‘best guess’ at the inaccurate or distorted information the brain receives from the eyes. This is usually the result of damage to the visual system from diseases like cataracts or glaucoma. For example, a shadow on the carpet could be mistaken for a hole in the floor or reflections in a mirror can be mistaken for an intruder.
  • Misidentifications – damage to specific parts of the brain can lead to problems identifying objects and people. For example, distinguishing between a son, husband or brother may become difficult or a green pillow might be called a "cabbage."

It is easy to see how these mistakes affect daily activities. They can lead to problems reading and writing, watching TV, moving around the home, and using the bathroom. Visuoperceptual errors can even lead to the person saying or doing strange things that make others think they are having delusions. However, what the person is experiencing is not a delusion; delusions are based on incorrect reasoning or "delusional thinking." These mistakes are the result of damage to the visual process involving the eyes and brain.

A Word About Hallucinations and Delusions

People with Alzheimer’s can experience hallucinations and delusions, but these are different from visuoperceptual mistakes. A visual hallucination involves perceiving or seeing something that is not there in the real world. (as simple as seeing flashing lights, or as complex as seeing animals or people). Hallucinations are sensory experiences that are imagined and can involve a combination of the senses -- what a person sees, smells, hears, tastes, or feels.

Charles Bonnet syndrome hallucination of a blue moose

 

There is also another condition worth mentioning which can cause hallucinations in people with vision loss-- Charles Bonnet Syndrome. This type of hallucination is solely visual and explained as a mirage or "phantom vision" of sorts. It usually occurs in older adults who are mentally healthy. Sometimes consultation with a neurologist or other specialist is necessary to rule out any serious disorders that may mimic Charles Bonnet syndrome [such as migraine, epilepsy, brain tumors, dementia, Parkinson's disease, or mental illness, for example]. For most patients, however, just knowing that they aren't becoming mentally ill and that the symptoms will eventually subside is all the treatment they need. Treatments and interventions are discussed in the section referenced on Charles Bonnet.

Unlike a hallucination, a delusion involves a set of false beliefs. An Alzheimer’s patient with delusions may become suspicious of the people around them, believing that caregivers are trying to trick them or steal from them. Delusions are based on incorrect reasoning or "delusional thinking." Memory loss and cognitive changes create confusion and seem to contribute to such irrational beliefs.

Be sure to read Tips for Caregivers on Reducing Visuoperceptual Difficulties in Individuals with Alzheimer's for more information on what to do.

Additional Information

Alzheimer's Overview

Tips for Vision Loss and Dementia.

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