Understanding Blindness and Vision Loss: It’s Not Always Total Darkness

When you hear that someone is blind, what do you picture?

For a lot of people, it's complete darkness. They picture someone who can't see anything at all.

But that's only one experience of blindness.

Someone may be able to see you standing in front of them but not recognize your face. Someone else might see what's directly in front of them but not the chair sitting a few feet to the side. Another person may see light, shadows, colors, or movement without being able to make out details.

Two people can both be considered blind or visually impaired and experience the world completely differently.

That's because vision loss is a spectrum.

Blindness, Low Vision and Legal Blindness

Before getting into the different patterns of vision loss, there are a few terms that are important to understand.

Low vision means someone has significant vision loss that makes everyday activities difficult and isn't fully corrected with standard glasses, contacts, medication, or surgery. A person with low vision may still have quite a bit of usable sight.

Legal blindness doesn't mean someone can't see anything. In the United States, a person is generally considered legally blind if, in their better eye with the best correction, their vision is 20/200 or worse, or their visual field is limited to 20 degrees or less.

Total blindness, sometimes documented as no light perception (NLP), means a person cannot perceive light at all.

But how someone experiences vision loss can be just as important as how much vision they have.

Visual Acuity vs. Visual Field

When we talk about eyesight, there are two things that are easy to mix up.

Visual acuity is how clearly you can see details. This is the part commonly measured with an eye chart.

Visual field is how much of the area around you you're able to see while looking straight ahead.

Someone can have fairly good central vision but a very limited visual field. Another person may have a wide visual field but struggle to see details directly in front of them.

That's one reason someone's ability to read an eye chart doesn't tell you everything about how well they can actually navigate their everyday life.

Central Vision Loss

Central vision loss affects what someone sees directly in front of them.

A person may be looking right at your face but have difficulty seeing your features. Reading, recognizing people, watching television, looking at photographs, or doing detailed tasks can become difficult.

A blind or significantly impaired area within the visual field is called a scotoma. When that area affects the center of someone's vision, it may be called a central scotoma.

And a blind spot doesn't necessarily look like a black circle or hole.

Our brains are pretty incredible at working with the information they're given. Sometimes the brain can fill in or compensate for missing visual information, meaning a person may not immediately realize that part of their visual field is missing.

Macular diseases, including age-related macular degeneration, can cause central vision loss.

Peripheral Vision Loss

Peripheral vision is your side vision—the things you can see without looking directly at them.

When peripheral vision becomes severely limited, people sometimes describe their remaining vision as tunnel vision.

They may be able to see what is directly in front of them while missing a person approaching from the side, a chair beside them, or an object on the floor.

Glaucoma is one condition that can gradually damage peripheral vision.

Hemianopia

Hemianopia, also called hemianopsia, means losing half of the visual field.

For example, someone may not see the left half of their surroundings from either eye, even though their eyes themselves may still be functioning.

This type of vision loss can happen after a stroke or other damage to the brain's visual pathways.

Imagine looking at a dinner plate and only noticing the food on one side. Or walking through a doorway and repeatedly bumping into the same side.

It isn't necessarily that the person isn't paying attention. They may genuinely not be seeing that part of their world.

Vision Loss vs. Visual Neglect

There's another condition that can happen after a stroke or brain injury that can look similar to visual field loss: hemispatial neglect, sometimes simply called visual neglect.

They're not the same thing.

With hemianopia, part of the person's visual field is actually lost because of damage to the visual pathway.

With neglect, the brain has difficulty paying attention to or recognizing things on one side of the person's space.

For example, someone might eat everything from one side of their plate and leave the other side untouched, groom only one side of their body, or repeatedly overlook objects on one side.

A person can experience visual field loss, neglect, or sometimes both at the same time.

Quadrantanopia

Quadrantanopia means approximately one-quarter of the visual field is lost.

Depending on where the damage occurs along the visual pathway, someone may lose vision in an upper or lower quarter of their visual field.

This can also happen after strokes, brain injuries, or other neurological conditions.

Night Blindness

Night blindness, medically called nyctalopia, means someone has significant difficulty seeing in darkness or low-light conditions.

A person might function fairly well during the day but struggle considerably more at night, in a dark hallway, or when moving between brightly lit and darker areas.

Cerebral or Cortical Visual Impairment

Not every vision problem begins with the eyes.

Cerebral or cortical visual impairment (CVI) occurs when the brain has difficulty processing or interpreting visual information because of damage or differences affecting the brain's visual pathways or processing areas.

Someone's eyes may be able to receive visual information, but their brain has difficulty making sense of it.

CVI can look very different from one person to another.

Other Problems That Can Affect Functional Vision

There are also vision problems that aren't technically "types of blindness" but can greatly affect someone's ability to see and function.

Diplopia means double vision.

Photophobia means abnormal sensitivity or intolerance to light.

Blurred or distorted vision can make objects difficult to identify even when the person knows they're there.

Color vision deficiency affects someone's ability to distinguish certain colors. A much rarer condition called achromatopsia can cause little or no color perception along with other visual problems.

Someone can also experience cloudy, wavy, washed-out, or distorted vision depending on the condition affecting their eyes or brain.

What Causes Vision Loss?

There isn't one cause.

Vision can be affected by conditions such as:

• Age-related macular degeneration

• Glaucoma

• Diabetic eye disease, including diabetic retinopathy

• Cataracts

• Retinal diseases or injuries

• Eye trauma

• Stroke

• Brain injury

• Neurological conditions

And not every change in vision has the same outcome.

Some causes of vision loss can be treated or improved. Cataracts, for example, can often be treated surgically. Other damage may be permanent, while some conditions are progressive and can cause vision to worsen over time.

That's why changes in vision should be evaluated by the appropriate medical professional instead of assuming that vision loss is simply a normal part of aging.

Sudden Vision Loss Is an Emergency

Gradual vision changes and sudden vision changes are very different situations.

Sudden loss of vision or a major sudden change in someone's eyesight needs immediate medical attention.

This is especially important if the vision change happens along with symptoms such as weakness or numbness on one side, trouble speaking, confusion, severe headache, dizziness, or difficulty with balance.

Those can be warning signs of a stroke or another medical emergency.

When vision suddenly changes, don't wait around to see if it gets better.

Don't Assume What Someone Can See

This is one of the biggest things I've learned through caregiving.

If someone tells you they're blind or losing their sight, don't assume you know what they can and cannot see.

Ask.

“Can you see this?”

“Would more light help?”

“Can you see better if I put it on this side?”

“Would you like me to describe where it is?”

“Do you want some help, or do you want to try first?”

Those questions may seem small, but they allow the person experiencing the vision loss to tell you what their world looks like.

Because blindness doesn't always mean darkness.

A person might see half the room. They might see through a small area of usable vision. They might see shadows but not faces. They might see well in one situation and struggle tremendously in another.

Understanding blindness starts with understanding that there isn't one single way to be blind.

And once we understand what someone can see, we can start learning how to help them without taking away the independence they still have.

That's what we'll talk about in Part Two.

Kayla