Scotopic Vision (Night Vision)

Scotopic vision (night vision) is the ability to see in dim light or low light. You use your scotopic (sko-top-ick) vision when you’re outside at night, in a darkened space like a movie theatre or in a room when the overhead lights are turned down.

How does scotopic vision work?

Your ability to see in low light starts when there’s a change in the amount of light entering your pupil. For example, here’s what usually happens to your eyes when you walk into a dark room from being outside in bright daylight.

• Your pupils let light in your eyes. Light hits your retinas at the back of your eye. Light also hits the millions of photoreceptors that line your retina.
• Photoreceptors (rods and cones) are cells that detect light. They take light and convert it into information your brain uses to create what you see (vision).
• When you’re in low light, your pupils widen to let in more light. After a few minutes, a protein receptor called rhodopsin starts to activate the rods in your retina. This process takes about 30 minutes.
• Your rods detect low light and turn it into coded signals that go to your optic nerve.
• Your optic nerve sends those signals to your brain. Your brain then translates the signals into what you see in low light.
• You may notice that you don’t see colors when you’re in low light. That’s because rods don’t detect and process colors.

What conditions can affect scotopic vision?

Your night vision depends on healthy photoreceptors, especially the millions of rods in your retinas. Some conditions specifically affect your rods and cones. But conditions that damage your retinas often affect your photoreceptors. Conditions that may affect your scotopic vision include:

• Cataracts: This condition may affect the flow of light to your photoreceptors and your night vision. Night blindness (nyctalopia) is a cataract symptom.
• Cone-rod dystrophy: This is an inherited disorder that makes your rods and cones break down.
• Macular degeneration: This disease affects your macula, the central part of your retina.
• Retinitis pigmentosa: This refers to a group of diseases that damage your retina through the breakdown of rods and, later, often cone photoreceptors.

How is night vision in humans different from night vision in animals?

There are several differences between human eyes and animal eyes. Animal eyes and pupils are larger than human eyes, so more low light gets in to trigger photoreceptor response.

Another difference is that we humans don’t have a tabetum lucidum. This is the layer of tissue behind animals’ retinas. The tissue acts like a mirror. When light passes through animals’ retinas, it hits the tissue. The tissue reflects light back to the rods in animal retinas to boost night vision.

How can I protect my night vision?

Good night vision relies on healthy photoreceptors (rods and cones) in your retinas. Here are some ways you can take care of your retinas:

• Have regular eye exams. This is a good idea even if you don’t need glasses or contacts. An eye care specialist will check your vision and eye health.
• Have annual physical exams. Issues like high blood pressure can affect your eye health. A provider can check blood pressure and other issues during your annual exam.
• Wear sunglasses with 100% UV protection (or UV400) and avoid staring right at the sun.
• Avoid nicotine. Nicotine can affect blood vessels in your retinas. That, in turn, may affect your photoreceptors.
• Emphasize good nutrition. The Mediterranean diet offers the most promise in protective benefits for the retina. The diet focuses on plant-based foods and healthy fats that have lots of antioxidants. It also helps reduce inflammation.