Night vision

Why your sight may suffer when it’s dark (and what you can do about it)

With shorter days in winter, people who have night vision problems may be particularly frustrated at this time.

Difficulties in being able to see at night are common. Yet rather than doing something about it, most people try to learn to live with it. The problem with that is, as well as being annoying, night vision deterioration can be dangerous, particularly when it comes to driving.

Many people who find it difficult to focus at night or find glare from oncoming headlights and traffic lights debilitating often suffer from astigmatism, where the curvature of the eye causes distortion of light. This may be corrected by wearing prescription lenses with anti-glare coatings in order to improve contrast, reduce glare sensitivity and improve depth perception.

A more serious extension of this problem is night blindness (also called nyctalopia), where people find it almost impossible to see in the dark. This is particularly common when moving from a light to a dark place.

So what causes a person to lose their quality of vision at nighttime – and what can they do about it?

What is night vision loss?

Night vision loss and night blindness are both due to a disorder of the cells in the retina that are responsible for seeing in dim light. You may be surprised to know that night vision actually does differ from your day vision.

When it’s dark, your eyes are, in effect, colour blind – the eye sees only a fraction of what it sees in daylight. A central scotoma (an area of diminished vision) appears in the centre of the visual field and your eye can’t detect an object that is stationary as well as it can detect moving objects.

What can cause night vision loss?

There are a number of reasons for night vision loss, from vitamin A deficiency to cataracts to the serious degenerative eye disease, retinitis pigmentosa.

• Vitamin A deficiency: Most people in the developed world aren’t at risk of vitamin A deficiency because they have access to nutritional food. However, occasionally deficiency can occur. Speak to your GP if you are concerned about vitamin A deficiency.
• Cataracts: A cataract is the clouding of the natural lens of the eye. Because it is most commonly the result of natural ageing process, cataracts usually present themselves later in life, particularly after a person reaches their 60s.
• Genetic defects: Issues such as retinitis pigmentosa and Usher syndrome can cause night blindness.
• Glaucoma: Because glaucoma affects vision in general, night vision also becomes an issue. If a person who has glaucoma has lost side vision, is sensitive to light and finds moving images such as cars become blurred, they should consider not driving, day or night.

Symptoms of night vision loss

If you suffer from this problem, it’s easy to tell. The sole symptom of night vision loss is, naturally, difficulty seeing in the dark.

You are more likely to suffer from night vision problems when transitioning from a bright environment to an area of low light. You are also likely to experience poor vision when driving, due to the intermittent brightness of headlights and streetlights on the road. Specific symptoms include:

• Blurred vision at night, particularly reading or close viewing
• Haloes around lights, particularly street lights and oncoming traffic lights
• Sensitivity to light or glare.

Problems with night vision can make it difficult for you to do some of the things that you enjoy – reading, crosswords and crafts such as woodwork, knitting or crocheting can be compromised. This can be very frustrating and concerning.

Prevention of night vision problems

Some causes of night vision loss, especially the more serious night vision losses such as birth defects or genetic conditions, cannot be prevented. However, for many of us, eating a balanced diet can make night vision problems less likely.

Eating a diet rich in antioxidant vitamins and minerals, including high levels of vitamin A may reduce risk of night blindness. Such foods include:

• rockmelon
• sweet potato
• carrots
• pumpkin
• mango
• spinach and other greens
• milk and eggs.

Eating a balanced diet and being aware of your limitations – especially when driving – are the best ways to handle night vision problems. However, if you find that your night vision is deteriorating, it’s important to see your optometrist or GP as soon as possible.