Night Vision

What is night vision?

Night vision is the ability to see in dim or dark light. Other names are scotopia or scotopic vision. This is the opposite of the ability to see in daylight, or photopic vision.

How does night vision work in the human eye?

Your eyes and brain work together to allow you to see in daylight, artificial light and darkness. They both work together to turn electrical signals into images.

Parts of your eye include the cornea, the pupil and the iris. The dome-shaped cornea bends the light that enters your eye through the pupil, which is the black opening in the middle of your iris. The iris is the colored part of your eye. It acts like a muscle to make the pupil smaller when light is bright and larger when the light is dim.

Your eyes have rods and cones, also called photoreceptors, which are responsible for capturing photons (light) and converting the light energy into signals that travel to the brain. You have about 6 million cones and 120 million rods in your retina.

Cones are responsible for color vision. The main location of cones is in the center of the eye in the macula.

Rods are responsible for vision in dim or dark light. They are located on the outer edges of the retina and help with peripheral (side) vision. Rods don’t provide color vision, so night vision is only in black and white.

Rods are much more sensitive to light — 500 to 1,000 times more sensitive — than cones are.

Why don’t humans have night vision like some animals do?

Human eyes are different from animal eyes. Animals that can see well in the dark have:

• Bigger eyes than humans.
• Wider pupils than humans, which let in more light.
• An eye part called a tabetum lucidum, a membrane that reflects light back to the retina.

How is your vision different at night?

At night, there is no color vision. You just see shades of gray and white.

How far can the human eye see in daylight?

People with 20/20 vision can see a long way in daylight. People can see about three miles away before the horizon goes out of sight because of the curve of the Earth. However, humans can see buildings and stars that are much farther away than three miles.

What is night blindness?

Night blindness refers to your inability to see well at night or in poor light, like in a restaurant or movie theater. It’s often associated with an inability to adapt quickly to a poorly lit environment after being in a well-lit environment. Night blindness has another name — nyctalopia.

Night blindness isn’t a disease in itself, but rather a symptom of an underlying eye problem, usually a problem with your retina. It’s common for people who have myopia (nearsighted) to have some difficulty with night vision. This isn’t due to retinal disease but is due to optical issues.

What are the most common causes of night blindness?

Many things can cause night blindness. Here are some of them:

Glaucoma and medications that treat glaucoma

Glaucoma refers to a group of eye conditions that cause damage to the optic nerve. The optic nerve sends signals from your retina (neural tissue in the back of your eye) to your brain. Your brain relies on these signals to create images. Glaucoma is a common cause of blindness throughout the world. Glaucoma can cause night blindness. So can medications that treat glaucoma by constricting your pupil (making the pupil smaller), like pilocarpine. Your pupil is the black opening in the middle of your iris. It gets smaller in bright light and bigger when it’s dark.

Cataracts

A cataract develops when the clear lens of your eye becomes cloudy and makes it difficult to focus light the same way. Cataracts are very common. More than 50% of people over the age of 80 have or had cataracts. Cataract surgery is the typical treatment for cataracts.

Retinitis pigmentosa

Problems with night vision is one of the early signs of retinitis pigmentosa (RP), a group of inherited eye disorders that affect your retina. RP is the most common inherited eye disease. It generally affects both eyes. Most people with RP have low vision. Some do go blind.

Vitamin A deficiency

Vitamin A deficiency is another cause of night blindness. This is true especially in people who’ve had intestinal bypass surgery. You need vitamin A to make rhodopsin, which your body needs for night vision. Vitamin A deficiency is rare in the U.S. It can happen if your diet is lacking in vitamin A or if you can’t absorb the nutrients you need. In addition to your eyes, vitamin A deficiency can affect your skin, hearts, lungs, tissues and your immune system.

Diabetes

Diabetes involves blood glucose (sugar) levels that are too high. Diabetes can affect your body in many ways, including causing blurred vision and night blindness. It’s important to try to keep your glucose levels stable. If you have diabetes, it’s also important to have regular appointments with an ophthalmologist. They will monitor you for conditions such as glaucoma and cataracts.

Age-related macular degeneration

Age-related macular degeneration (ARMD) is an inherited eye disease that affects central vision but spares peripheral vision (being able to see things off to the side). It’s the leading cause of vision loss in people in the U.S. It occurs in people over the age of 50 and can affect one or both eyes.

There are two forms of the disease: dry and wet. Dry ARMD happens when yellow deposits called drusen form in your macula. Your macula becomes thin and dry. With the wet form, you develop abnormal blood vessels that leak under your macula and retina. This causes a build-up of fluid that makes your macula bulge.

What tests will your healthcare provider do to diagnose the cause of night blindness?

To determine what is causing your night blindness, an eye care specialist will perform a thorough eye exam that includes asking questions about your medical history and other symptoms. Your provider may order other tests, including:

• Electroretinography: This test measures your retina’s response to light.
• Pelli-Robson contrast sensitivity chart: This test is similar to the Snellen eye chart that shows letters on a white background. The letters on the Pelli-Robson chart go from black to progressively lighter shades of gray.
• Blood tests: Your provider may ask for blood tests to measure your levels of vitamin A and glucose.

Can you have 20/20 vision and not be able to see at night?

It’s possible to have difficulty seeing at night or in dim light and have 20/20 vision in daylight.

A note from Cleveland Clinic

Being able to see in dim and dark light is an ability that may fade over time, but you should always report this information to your healthcare team. This is particularly true if you have diabetes or other health conditions. It’s important for everyone to take care of their eyes. In addition to staying healthy through diet and exercise, you can do that by having regular eye exams.