Nyctalopia facts for kids

Quick facts for kids Nyctalopia
Synonym	Night blindness
Effect of night-blindness. Left: normal night vision. Right: night-blind.

Nyctalopia, also known as night blindness, is a condition that makes it hard or impossible to see well in dim light. It is a symptom of several eye problems. Night blindness can be present from birth, or it can happen because of an injury or not getting enough nutrients (like vitamin A deficiency). It means your eyes don't adjust enough to the dark.

The most common reason for nyctalopia is retinitis pigmentosa. This is a disorder where special cells in the retina (at the back of your eye) called rod cells slowly lose their ability to see light. People with this genetic condition have night blindness that gets worse over time. Eventually, their daytime vision might also be affected. In another type, called X-linked congenital stationary night blindness, the rod cells don't work well from birth, but the condition doesn't get worse.

Another cause of night blindness is not having enough retinol, which is also known as vitamin A. You can find vitamin A in foods like fish oils, liver, and dairy products.

The opposite problem, which is being unable to see well in bright light, is called hemeralopia. This condition is much rarer than night blindness.

The outer part of your retina has more rod cells than cone cells. This means that if you lose your peripheral vision (your side vision), it often leads to night blindness. People with night blindness not only see poorly at night but also need extra time for their eyes to get used to dim areas after being in bright ones. Their ability to see differences in light and shadow (contrast vision) can also be much lower.

Rod cells contain a special protein called rhodopsin. When light hits rhodopsin, it changes shape and creates electrical signals. These signals are then sent to your brain through the optic nerve, allowing you to see. In the dark, rhodopsin is rebuilt. Your body makes rhodopsin using vitamin A. This is why not having enough vitamin A can cause poor night vision.

Sometimes, eye surgeries like refractive "vision correction" surgery (especially PRK) can rarely cause a slight reduction in how well you see at night. This can happen if the surgery affects how your eye handles light, making it harder to see contrasts in dim light.

What Causes Night Blindness?

Night blindness can be caused by different things, including:

• Retinitis pigmentosa: A genetic eye disease that damages the retina.
• Retinal detachment: When the retina pulls away from the back of the eye.
• Certain medications: Some medicines, like phenothiazines, can affect vision.
• Oguchi disease: A rare genetic eye disorder.
• Pathological myopia: A severe form of nearsightedness.
• Cataract (peripheral cortical): A clouding of the eye's lens, especially around the edges.
• Refractive surgery: Eye surgeries like LASIK, photorefractive keratectomy, or radial keratotomy.
• Sorsby's Fundus Dystrophy (Macular degeneration): A genetic eye disease that affects the central vision.
• Vitamin A deficiency: Not getting enough vitamin A, often leading to xerophthalmia (dry eyes).
• Choroideremia: A genetic eye disease that causes progressive vision loss.
• Glaucoma: A group of eye conditions that damage the optic nerve.
• Visual snow: A condition where people see tiny flickering dots across their vision.

Night Blindness in History

People have known about night blindness for a very long time. Around 30 AD, a Roman writer named Aulus Cornelius Celsus described night blindness. He even suggested eating liver, which we now know is a great source of vitamin A, to help with it.

In the past, night blindness was sometimes called moonblink. People thought it was a temporary condition caused by sleeping in moonlight, especially in tropical places.

During the American Civil War, night blindness (sometimes called gravel) was reported among soldiers. It was often seen with other signs of poor nutrition, like scurvy. At first, some people thought soldiers might be faking or exaggerating their night blindness.

Night Blindness in Animals

Night blindness can also affect animals. For example, a type of night blindness called congenital stationary night blindness (CSNB) is found in horses with leopard spotting patterns, like the Appaloosa. This condition is present at birth, doesn't get worse, and affects their vision in dim light.

Horses with CSNB might have eyes that don't line up correctly (dorsomedial strabismus) or their eyes might move on their own (nystagmus). Since the 1970s, scientists have linked CSNB in horses to the leopard complex color pattern. A study in 2008 suggested that both CSNB and the leopard spotting patterns are connected to a gene called TRPM1. This gene is important for how nerve signals are sent in the eye and skin.

See also

In Spanish: Nictalopía para niños