Most of us hear about night blindness being a problem with vitamin deficiencies, and specifically a vitamin A deficiency. However, this is an uncommon cause of a relatively common problem. Despite its name, a person does not go blind (complete loss of vision) at night. Instead it refers to a difficulty with sight at night which is a common symptom of many different eye and vision conditions.
What is night blindness?
Night blindness, also known by the medical term nyctalopia, is a condition where the eyesight is poor in dimly lit environments. This is most obvious at night. However, even being in a poorly lit room during the day with no significant natural or artificial light sources can equally be a problem. While humans do not have very good night vision as compared to certain species of mammals, in night blindness there is a significant and abnormal impairment of eyesight at night.
Causes of Night Blindness
How does night blindness occur?
Light from an object enters the eye and is bent first by the cornea and then by the lens to focus an image on the light-sensitive tissue known as the retina. Specialized receptors cells in the retina, known as rods and cones, convert the light impulses into nerve signals. These signals are then carried by nerves to the visual cortex of the brain. Here it is interpreted to allow us to perceive the light and is broadly known as the sense of vision.
However, for this to occur there has to be light reflecting off or radiating from an object in the environment. Some objects radiate their own light like the sun or an electric lamp. Other objects do not radiate light but instead reflect light in the environment. When there is insufficient environmental light like in a dark room or at night then our ability to see objects is significantly diminished an this is considered normal.
The intensity of the radiated or reflected light stimulates the rods and cones to different levels. An abnormality in stimulation of the photoreceptors with dim or poor light impairs the ability to see at night as others would. A pigment within rods, known as rhodopsin, undergoes changes that generate electrical signals. This pigment is regenerated using vitamin A. Therefore vitamin A deficiency can affect rhodopsin regeneration and lead to night blindness.
What conditions cause night blindness?
Some causes of night blindness are obvious as the condition impairs the entry of light as it passes to strike the retina. Others have a more complex connection to night blindness. The causes can be divided into treatable and non-treatable.
Non treatable causes include:
- Birth defects like X-linked congenital stationary night blindness where the rods are non-functional or under-functioning.
- Retinitis pigmentosa is a condition where the retina (the light-sensitive inner lining of the eye) degenerates. It is incurable.
Treatable causes include:
- Cataracts where the lens becomes cloudy thereby reducing the intensity of light passing through it and eventually blocking the light completely (blindness).
- Myopia (nearsightedness) when uncorrected with spectacles, contact lenses or refractive surgery impairs the ability to see at night due to the elongation of the eyeball and failure of the lens to compensate.
- Drugs like those used for glaucoma which constrict the pupil and therefore limit the amount of light entering the eye.
- Diabetes which is long-standing and poorly controlled can lead to diabetic retinopathy where the retina becomes diseased as a result of damage to the tiny capillaries supplying it.
- Vitamin A deficiency is an uncommon cause of night blindness contrary to popular belief. As explained the deficiency means that rhodopsin, the pigment in rods, cannot be regenerated.
Signs and Symptoms
In night blindness a person has difficulty seeing at night or in a dimly lit root. However, in milder cases a person may not clearly identify this visual impairment. Rather there is a change in their behavior such as opting to use brighter light or avoiding night driving. Eventually a person realizes that there behavior change is due to difficulty seeing with lower light intensity.
Another common feature of night blindness is the prolonged adaptation when moving from a bright to dark room. Most of us need a few seconds to adapt when moving from a very bright environment to a dark area like a movie theater. However, in people who suffer with night blindness it can take a significant period of time to adapt, if at all and can even lead to accidents, like falling.
Treatment of Night Blindness
The treatment should be directed at the underlying cause of night blindness. This is only possible for the treatable causes. People with non-treatable night blindness will have to make lifestyle changes to deal with the condition.
- Cataracts usually require lens removal and replacement surgery (cataract surgery).
- Myopia (nearsightedness) can be corrected with eyeglasses, contact lens or LASIK surgery in most cases.
- Vitamin A deficiency can be treated and prevented with vitamin A supplementation and dietary change.
- Medication that cause night blindness can be stopped or replaced with other drugs.
- Diabetic retinopathy can be managed with proper glucose control and treated with laser or surgery.
It is important to note that early treatment is often more effective as is the case with most conditions.
Prevention and Management
By treating the above conditions early it is possible to prevent night blindness. Vitamin A supplementation as a preventative measure will only be effective for night blindness due to vitamin A deficiency. It is ineffective against other causes and high doses of vitamin A can lead to toxicity. Management involves lifestyle measures that can limit the extent to which night blindness impacts on daily life and has to be considered for non-treatable causes.
- Use brighter light where necessary. This may involve brighter artificial lighting, allowing more sunlight into the home or office where possible or even carrying and using a small light source like a flashlight.
- Avoid driving at night if there is significant impairment of nighttime vision. It may be inconvenient but it can prevent serious road traffic accidents that can be fatal.
- Do not enter areas with poor lighting after being in bright light if it can be avoided. Mishaps may occur which can lead to serious medical outcomes. While most people may expect their eyes to accommodate in due course, a person with night blindness can find themselves lost within an area with poor lighting or even bump into objects or fall.
- Undergo regular eye examinations to monitor the eyesight impairment. Early treatment of some conditions can minimize the severity of the condition and even reverse it.