What is night blindness?
A general night blindness definition is difficulty seeing clearly in low light or at night. Night blindness can make it harder to see when you go from a well-lit situation to dim lighting or darkness. It may also take your eyes longer to adjust to this transition. The medical term for night blindness is nyctalopia.
In low light, the eye reacts in several ways. First, the iris—the colored part surrounding the pupil—dilates, making the pupil wider. This allows more light to enter the eye and hit the retina—the area at the back of the eye that senses light. Night blindness can be situational and temporary with quick exposure to bright light and a return to darkness, such as from oncoming car headlights. The iris rapidly constricts in reaction. When it opens back up, it takes some time to adjust. In the meantime, you have impaired vision.
The retina contains two types of cells called photoreceptors. Cones are the photoreceptors that perceive color and light, but they work best in bright light. Rods mainly detect light, and are most active in dim light. In dim light or darkness, the eye turns on as many rods as it can. Cones, on the other hand, aren’t very active. As a result, vision in low-light environments is mostly dependent on rods and appears primarily in black and white. Chronic night blindness occurs when there is a problem with the rods and they stop working the way they should.
Night blindness is not a condition, but rather a symptom of another eye problem. Night blindness causes include retina disorders, medications, and optical issues, such as nearsightedness. Problems with night blindness tend to increase with age due to normal changes in the eye. This includes having fewer rods and decreased responsiveness of the iris.
Because it is a symptom, night blindness treatment is entirely dependent on the underlying cause. However, there are some causes that are not treatable, such as birth defects of the retina. If you notice problems with your night vision, see your ophthalmologist promptly. A night blindness test can help identify the underlying problem. If it’s treatable, early intervention can get you back to seeing better in the dark.
What are the symptoms of night blindness?
In general, night blindness means it’s hard to see in the darkness or in dim light. In some cases, you may not be able to see at all in low-light environments.
Common symptoms of night blindness
Common night blindness symptoms include:
- Blurry vision
- Delayed vision adjustment when moving from light to darkness or darkness to light
- Difficulty seeing distant objects
- Seeing halos or glare around lights
See your eye doctor if you have these symptoms. Doctors often use a test called the Pelli-Robson Contrast Sensitivity Chart to diagnose night blindness. The chart has letters in shades of gray on a white background. It measures your ability to distinguish them. These symptoms may also be signs of other problems that your eye doctor will explore.
What causes night blindness?
Night blindness is a symptom of several underlying conditions. It occurs when the rods—photoreceptor cells in the retina of the eye—stop working. Rods perceive light and turn on in dimness or darkness. Problems with the rods fall into treatable and untreatable categories.
Untreatable causes of night blindness include:
- Birth defects or congenital night blindness
- Hereditary retinal dystrophies
- Retinitis pigmentosa, which is a genetic condition that changes the way the severely degenerated retina responds to light
Treatable causes of night blindness include:
- Cataracts, which is clouding of the lens that can make vision dim and increase glare and light distortion
- Diabetes, which is high blood sugar that can damage the blood vessels of the eye and retina, causing retinopathy
- Glaucoma, which is increased pressure inside the eye that can damage the retina
- Macular degeneration, which is a retinal disease
- Medications that constrict the pupil, including glaucoma drugs
- Myopia, which is nearsightedness
- Vitamin A deficiency, which is rare in the United States
Your doctor can determine the cause of night blindness by conducting a complete eye exam. Advanced eye tests may also be necessary.
What are the risk factors for night blindness?
Risk factors for night blindness include:
- Being nearsighted
- Having a medical condition that can damage the retina or make vision dim
- Having genetic conditions that cause night blindness
- Taking medicines that constrict the pupil
Reducing your risk of night blindness
You may be able to lower your risk of night blindness by controlling medical conditions that can cause night blindness, such as diabetes and glaucoma. It’s also important to get regular eye exams to help identify potential problems early and adjust prescriptions as needed.
How is night blindness treated?
Night blindness is a symptom of another eye problem, so treatment completely depends on the underlying condition. For nearsightedness, this may simply be a matter of updating your prescription. For cataracts, it may involve surgery to remove them. For diabetes, controlling your blood sugar levels can help prevent progression of diabetic retinopathy. If medications are causing the problem, switching to another drug may help.
When a genetic condition is the cause, night blindness may not be treatable. A retinal specialist has the expertise to accurately diagnose the cause of night blindness and recommend potential solutions.
What are the potential complications of night blindness?
Night blindness can significantly affect your quality of life and ability to live day to day. It can make it difficult to recognize people and objects at night or in dimness. It also increases the risk of falling and can make it impossible to drive at night.