Vision

What is vision?

Vision is the process where your eyes and brain work together and use light reflecting off things around you to create the ability to see. It’s one of the five main senses and a key contributor to how most people understand the world around them.

How does vision work?

Vision starts when your eyes detect light and turn it into coded nerve signals, which then travel through your optic nerves to your brain. Your brain receives and decodes the signals, and turns them into the pictures you see.

Eyes

An easy analogy is to think of eyes like cameras, but it’s really the other way around. Cameras are an example of technology reverse-engineered from the human eye.

Cameras have lenses that focus light onto a special sensor inside the camera. That sensor converts light into electrical signals, and a special computer inside the camera translates those signals into the data that makes up the image file. You can also control the focus of a camera, and some cameras let you control how much light reaches the sensor.

Your eyes have lenses that focus light and direct it toward your retinas. Your retinas are like the sensor inside the camera, but far more sophisticated. They convert the light that lands on them into nerve signals and then send those signals to your brain. This happens dozens of times per second.

And the special capabilities of cameras, like focusing and light control, are also things your eyes do automatically. Your pupils can widen (dilate) or narrow (constrict) to control how much light enters your eyes. Muscles control your eyes’ lenses, changing how light rays come into focus for objects at varying distances.

Retinas

Your retinas are highly specialized, very sensitive cells called photoreceptors (meaning “light receivers”). When light hits them, it triggers chemical and electrical reactions in the cells. That’s how those cells convert light and encode them into nerve signals.

There are two main types of photoreceptors:

• Rods: These mainly detect differences in brightness. They help you see in dim or dark places.
• Cones: These photoreceptors are more sensitive. They can pick up more detail and detect different colors.

Once converted into coded nerve signal form, your retinas transmit the signals to your optic nerves.

Optic nerves

Your optic nerves are like data cables that link your retinas to various parts of your brain. The signals travel along the optic nerves to reach the various parts of your brain responsible for signal decoding and processing.

Brain

The last main step involves your brain. Your brain receives the coded signals carried along your optic nerves and decodes them. It then uses the decoded information to construct the “image” of what each eye sees.

Depending on what you see, your brain might have different areas working together to process and fully understand the picture. For example, reading a sentence like this also involves brain areas responsible for understanding language and recalling memories. That’s how you can understand the words, remember what they mean and use them to access related memories.

What conditions could affect my vision?

Vision involves multiple body parts and structures working together, and different conditions can affect each. Some conditions can affect more than one part of your visual system.

Examples of conditions that can affect your vision, depending on the affected part, include:

• Eye-related conditions.
• Retina- and optic-nerve-related conditions.
• Brain-related conditions.

What is visual acuity?

Visual acuity refers to how well you see. Experts use two numbers, set apart with a slash mark, to communicate this. The first number is how far away an object seems to you. The second number is how far away a person with normal visual acuity would have to be to see the object with the same clarity.

For example, normal visual acuity, also known as 20/20 vision, means you see an object that is 20 feet away correctly. If you have 20/15 vision, you see an object that's 20 feet away as clearly as most people would see it if they stood 15 feet away (meaning your vision is better than normal). If you have 20/40 vision, what you see 20 feet away from an object is what someone with normal vision could see from 40 feet away, meaning your vision is worse than normal.

What’s the difference between vision and sight?

Many people, experts and scientists included, use the terms “vision” and “sight” interchangeably. But they aren’t necessarily the same thing. It’s possible to use your visual abilities without seeing something (like seeing images in your mind). There are also brain conditions that affect your ability to process what your eyes detect.

One way to break this down is to look at sight as a physical ability only. It refers to how your eyes detect light and turn it into electrical and chemical signals to send to your brain.

Vision, on the other hand, requires the ability to process signals from your eyes. Without that processing, the signals your eyes send to your brain aren’t useful.

While it might seem strange to think of them separately, there are brain conditions that can affect vision without disrupting sight. Examples include visual agnosia and other agnosia-type conditions. People with visual agnosia have functioning eyesight, but their brains can’t always process what they see. A specific example of this is face blindness (prosopagnosia). People with this condition can see faces but can’t recognize them.

How can I protect and maintain my vision?

There are several things you can do to maintain and protect your vision. Some of the most important to keep in mind include:

• Get eye exams as needed. Everyone needs regular eye exams, even people with normal (20/20) vision. That’s because eye exams include tests on your eyes that can detect issues you can’t see. And decreases in vision from issues like refractive errors (like nearsightedness or farsightedness) often happen slowly and go unnoticed early on. An eye exam can catch them before you might notice them otherwise.
• Protect your eyes. Eye protection is a must whenever you’re in situations where something could damage your eyes. Safety goggles or glasses, face masks or shields and other protective items can help you do this. Sunglasses are also a form of eye protection, protecting your eyes from damaging UV rays.
• Nutrition matters. Your eyes need certain vitamins and nutrients to work properly. If you have questions about this, your primary care provider or an eye care specialist can offer recommendations and guidance.
• Make activity a priority. Your eye health reflects your overall health. Staying physically active can help maintain your eyes (as well as the rest of your body).
• Avoid tobacco use. Smoking, vaping and smokeless tobacco can negatively affect your health and vision. Quitting (or never starting) tobacco use can make a big difference.
• Don’t delay medical care if you have sudden changes in or loss of vision. These can be key symptoms that warn you of a bigger issue. Sudden, unexpected vision loss is always a reason to seek medical attention. If you have medical conditions that can cause sudden vision loss or changes, your healthcare provider or eye care specialist can also guide you on when you specifically need to seek care.