Night Blindness (Nyctalopia): Definition, Causes & Symptoms

What is night blindness?

Night blindness, also known as nyctalopia (pronounced “nik-tah-LOPE-ee-uh”), is when you have trouble seeing in dim or dark settings. It can happen if your eyes have trouble quickly adjusting to changes in brightness or have issues with detecting light.

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Night blindness is a symptom of other conditions, not a disease on its own. It’s possible with a wide range of conditions that can affect different parts of your eyes. Some forms develop when you’re a child, while others may not show up until you’re an adult.

How seeing in the dark works

The ability to see in low-light conditions — like in dimly lit rooms or at night — mainly involves two structures in your eyes:

• Retinas. The retinas at the backs of your eyes contain two types of light-detecting (photoreceptor) cells, cones and rods, which get their names from their shape. Cones handle color vision and fine details. Rods mainly handle vision in dim light. Rods make up about 95% of retinal photoreceptors and help your irises adjust how much they widen or narrow.
• Irises. The iris contains muscles that widen or narrow the opening of your pupil to adjust how much light can enter your eyes. If your irises don’t narrow quickly or far enough, too much light can enter your eye and overwhelm the cells in your retinas. This causes light sensitivity and can make it hard to see well in bright light. And if the irises don’t work correctly, making your pupil remain small, they can keep enough light from getting to your retinas. This prevents you from seeing in low-light situations.

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But nyctalopia can also happen with conditions that affect how light travels through your eyes. The tissues that make up the forward parts of your eyes need to be clear so light can pass through them. When they aren’t clear or don’t allow light to pass through them correctly, it limits how much light reaches your retinas and can cause difficulties seeing in dim light.

What are the signs of night blindness, or what does it feel/look like?

There are two main ways that night blindness can happen:

• Lack of light making it to your retinas. When this is the case, it can feel like the world you see is darker, blurrier or harder to focus on. It can happen because of issues affecting structures in your eyes that should be clear, conditions that affect your retinas, or when your irises don’t widen as they should in dim light.
• Retinal cells that don’t react to light correctly. Your retinas are light sensors, with cells that sense incoming light and convert the light into electrical signals that go to your brain. Some conditions are like a broken or burned-out sensor, meaning the cells react too weakly or don’t react at all.