Nyctalopia is the name for a symptom characterized by the reduced ability to see at night and in low light conditions. It is also called night-blindness. While it isn’t a medical condition in and of itself, it can be a symptom of another disorder.
There is some confusion over the definition for the term nyctalopia, which is sometimes mistakenly used to describe a condition called hemeralopia. In contrast to nyctalopia, hemeralopia is a rare condition in which a person is unable to see in bright light.
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What causes nyctalopia?
Normally, a person’s ability to see is reduced in the dark. The ability to distinguish colour is reduced, and static objects are harder to see than moving objects in dark conditions. There is also a portion of the central field of vision that is less clear when in darkness.
While everyone’s vision is impaired to a degree at night or in low light conditions, others experience significant difficulties in seeing in these situations, affecting their ability to walk or drive at night, or move around their house safely. Going to public places where light is generally low, such as cinemas, can also pose problems, as the eyes may adjust from bright light to darkness more slowly.
Being very short-sighted (myopic) is a common condition that can make seeing in dark conditions harder, but there are a number of other conditions that can cause nyctalopia, including:
- Glaucoma – a disease affecting the optic nerve connecting the eye and brain
- Glaucoma medications – specifically medications that cause the pupils to narrow
- Cataracts – clouding of the lens
- Diabetes mellitus – uncontrolled blood glucose levels
- Retinitis pigmentosa – a rare eye disease that causes the breakdown and loss of retinal cells, causing blindness
- Keratoconus – a very curved cornea
- Vitamin A deficiency
As the risk of developing some of these eye problems increases with age, older people are more likely to experience nyctalopia. Diabetes also increases the risk of developing eye problems, which then may lead to nyctalopia.
In the case of vitamin A deficiency, nyctalopia can develop because the receptor-protein necessary for seeing in low-light conditions requires the synthesis of rhodopsin from vitamin A. The ability to see depends on two photoreceptors found in the rods and cones.
Rods and cones are found at the back of the eye, in the outermost region of the retina, with rods being used for night vision, and cones being used for bright light vision. They are made up of various segments, the outer one being made up of discs containing photoreceptors that absorb light.
Vitamin A is converted to 11-cis-retinal which then combines with scotopsin to form rhodopsin in the rods. If there is a lack of vitamin A, adequate amounts of rhodopsin cannot be produced, thus reducing the ability to see in low light conditions.
In retinitis pigmentosa, a progressive loss of rods is experienced, affecting night vision, followed by the progressive loss of cones, which then affects daylight vision as well. It is a genetic disorder for which there is currently no cure.
How is nyctalopia diagnosed?
The following problems can prompt a visit to the doctor to discuss nyctalopia:
- Trouble moving around the house at night
- Difficulties driving at night
- Avoiding trips in the dark in case of falls or injuries
- Being unable to or experiencing delay in attempts to see or recognize faces in dark places
- Experiencing delays in adjustments from light to darkness
A complete history and eye exam will help to discover any underlying conditions that may be causing nyctalopia.
The treatments for nyctalopia will vary depending on its underlying cause. Sometimes all that is needed to correct nyctalopia is a new or adjusted prescription for glasses, a change in medication (for glaucoma, for example) or surgery, as when cataracts are the underlying cause of nyctalopia.
There are some conditions causing nyctalopia that cannot be treated, such as the genetic condition retinitis pigmentosa.
Maintaining good overall health is a good way to prevent eye conditions that can lead to nyctalopia. For instance, eating antioxidant- and vitamin-rich foods can help to minimize the risk of developing cataracts, and keeping blood sugar levels healthy can also prevent diabetes. These are two known risk factors for nyctalopia.
As nyctalopia is not a distinct condition itself, it is treated by addressing underlying eye or other health problems that may cause it. It is advised that those living with nyctalopia do not drive in dark conditions to ensure their own safety, as well as the safety of others. It is recommended that you speak to a health professional before beginning any vitamin supplements, if vitamin deficiency is thought to be the cause of nyctalopia. Maintaining a balanced and healthy diet can help prevent health problems that may lead to nyctalopia, and as such is a recommended preventative measure.