Your eyes need light to work. Sometimes people can have problems with bright light which can happen for a number of reasons.
Light rays enter the front of your eye through the clear cornea and lens. It is very important that both the cornea and lens are clear as this allows the light to pass directly through the front of your eye to the retina. The cornea and lens bend light so that it can focus on the retina at the back of your eye. The cornea focuses the light towards your retina and the lens fine tunes the focussing of this light. This gives you a clear, precise image.
The tears form a protective layer at the front of your eye and also help to direct the light coming into your eye.
The iris, the coloured circle at the front of your eye, changes the size of the pupil which allows different amounts of light into your eye.
Our pupil is the dark hole in the middle of the coloured part of your eye. The pupil gets smaller in bright conditions to let less light in and gets bigger in dark conditions to let more light in.
The middle of your eye is filled with a jelly-like substance called the vitreous. The vitreous is clear and allows light to pass directly from the front to the back of your eye.
The retina at the back of your eye is a light-sensitive layer which consists of rod and cone cells. These cells collect the light signals and send them as electrical signals to the optic nerve.
Rod cells are concentrated around the edge of your retina. They help you to see things that aren’t directly in front of you, giving you a rough idea of what is around you. They help with our mobility and getting around by stopping you from bumping into things. They also enable you to see things in dim light and to see movement.
Cone cells are concentrated in the centre of your retina where the light is focused by the cornea and lens. This area is called the macula. Cone cells give you your detailed vision which you use when reading, watching TV, and looking at people’s faces. They are also responsible for most of your colour vision.
The optic nerve is made up of thousands of nerve fibres. It’s the pathway for light signals to travel to your brain. The brain processes these signals to allow you to “see” the world around us.
Seeing can be likened to the process of taking pictures on a film with a camera which you then get developed. Your retina is like a camera film which stores an image of what you are looking at. The image directed onto your retina is then sent along to your brain where it is processed, like developing a camera film. Therefore you actually “see” in your brain with the light information sent to it from your eyes. This whole process happens very quickly so that everything you see is in focus.
We need light to see what is around us and its colour. Light bounces off the objects we look at and different objects will reflect different amounts of light.
Light entering our eyes is collected by our retina and processed by our brain to obtain the pictures that we need to see. Light is an essential part of this process, for example it is difficult to read when light levels are low. Sometimes light can cause problems for our vision.
There are times when the amount of light or the quality of that light can affect our ability to see. Many people with low vision need more light than usual to read. However, too much light can cause problems with glare.
Glare is when a light source affects our ability to see clearly. There are two types of glare; discomfort glare and disability glare.
Discomfort glare occurs when a light source is just too strong for our eyes. It may cause us to screw up or shade our eyes; it can even cause us to close our eyes.
A good example of when we might experience discomfort glare is when we leave a dark room and move into bright sunlight. As our eyes adjust the light feels uncomfortable and sometimes painful. Usually our eyes adjust to the new level of light and we are able to see clearly again after a few seconds. Our eyes adjust to the new level of light by making our pupil smaller (constricting). As the name suggests, discomfort glare can make our eyes feel uncomfortable.
Disability glare reduces how well we can see. Disability glare can be caused by eye conditions and can occur with ordinary light sources and levels of light.
The structures of our eyes are normally clear which means light can pass smoothly through our eye. As we age certain eye conditions can make our eye’s structures less clear. The most common example of this is a cataract.
If you have a cataract, the lens in your eye is not as clear as it should be. This causes the light entering your eye to scatter as the light is unable to pass smoothly through your lens. This effect, as well as making things unclear and blurred, also makes coping with bright light difficult. The amount of light scatter depends on the amount of light entering your eye and how advanced your cataract is. A brighter light will scatter more and cause more glare. People with cataracts often have a lot of trouble with glare.
Some eye conditions can cause glare, including:
There are also some other conditions such as meningitis which cause light to be very painful quite quickly.
Some drugs taken for other conditions can also cause light sensitivity. Examples can include tetracycline, an antibiotic, and digitalis, a drug used for heart problems.
If you start to experience light sensitivity, it’s important to see an optometrist to have your eyes checked. An optometrist will be able to examine the health of your eyes to check for any underlying eye condition which may need treatment.
If your light sensitivity comes on very suddenly then it should be checked as soon as possible in case it is the first sign of a more serious condition such as meningitis.
Treatment for light sensitivity depends on the cause. Usually if the light sensitivity is a symptom of an underlying eye problem such as cataract, then treatment for your cataract can solve the glare problem. Treating eye conditions, like uveitis, often means that your eye becomes less light sensitive.
Unfortunately not all light sensitivity caused by eye problems can be treated, for example, the light sensitivity caused by macular degeneration. If this is the case then you may have to use other ways to help you cope with bright light.
The most obvious way to cope with glare is to limit the amount of light that’s entering your eye. Shading your eyes with your hand or wearing a hat with a wide brim can help cut down on glare with little expense.
Tinted lenses help to minimise the light entering your eyes and so cut down on the amount of glare you experience.
Sunglasses should have an UV filter so they also protect your eyes from the harmful UV rays of the sun. The best lens will have protection against both UVA and UVB light.
Some people prefer to have light activated sunglasses, which get darker in brighter conditions, though this is a personal choice.
Polarized lenses can cut down on reflected glare from flat surfaces, for example light reflected off water or snow or off the bonnet of a car.
There are sunglasses, sometimes called solar or UV shields or wrap-around shades, which are larger than normal. They have built in sides which stop the light entering that way and they are also made to stop the light entering from above your eyes. They can also be worn over your normal spectacles and come in a variety of tints. These can be very helpful but the fit of them is important. Everyone has a different shaped head and it’s useful to try on several pairs of wrap-around sunglasses to find the ones which fit closest and stop the most light from coming in around the edge of the frame.
A low vision specialist can give you advice on coping with glare. They can talk to you about the best way to use lighting to avoid glare. This is especially important since it can be difficult to balance the amount of light someone with a sight problem needs for tasks such as reading and the fact that they may have a problem with glare.
Some eye conditions can make moving between areas with different lighting levels difficult. For example, when moving from sunlight into a dim room, or vice versa. It may be necessary to pause and put sunglasses on or take them off and give your eyes time to adjust. It’s important that you don’t feel rushed and to give yourself time. Often, these changes in light levels occur at the entrance to buildings, which can be particularly dangerous as there are often steps in these places.
Many people with a sight problem find that using a task light for activities such as reading helpful. The best lights for this type of task are adjustable lamps so that you can direct the light to where you need it the most. The best position for an adjustable lamp when you need more light for a task is between you and what you want to look at, directed at the task, below your eye level. This can reduce the amount of glare.
There is much more information on lighting and low vision in our Starting out – Making the most of your sight leaflet.
Some people have light sensitivity even though they don’t have an eye condition. It’s still important, if you begin to experience light sensitivity, to have your eyes checked by an optometrist (optician) as there may be an eye condition that hasn’t yet been picked up. Unfortunately some people are sensitive to light without there being a physical cause.
It’s important to remember that there is a range of light sensitivity. Some people are just more sensitive to light than others. Also as we grow older we can also become more sensitive to light; this is because our eye changes even though there is no underlying eye condition.
Even though there may be no physical cause for your light sensitivity it can sometimes be very intense. The advice about sunglasses and hats can often help anyone with light sensitivity. Wearing correct sunglasses will not harm your eyes or make them lazy.
Using the least amount of tinted lenses while you are inside is best because the darker things are, the more the light will bother you. It is important to get advice from your optician on what tints or level of tint to wear during the day when driving to make sure your lenses allow enough light in for safety and meet any DVLA regulations. The Highway Code warns against using any form of tint for night driving. You may want to talk with your optometrist about using clear lenses with an anti-reflection coating. Some people find that they can help to reduce glare when driving at night. Your optician will be able to explore this further with you.
People who suffer from migraine tend to be more sensitive to light, to a marked degree during a migraine headache and also to a lesser degree at other times. Sometimes, certain types of light or patterns can trigger migraine. Some people with migraine may therefore benefit from special tinted lenses, called precision tinted lenses. These can also help people who experience glare from pages of text, including some people who have dyslexia. Precision tinted lenses are discussed below.
Coloured lenses with particular tints limit certain wavelengths of light and are often used to help people with light sensitivity. The colours of these tints range from yellow to reds to blues. At the moment there is no strong evidence that a particular shade of tint suits one eye condition over another and it would appear that choosing the tint is a matter of personal choice. For example two people with macular degeneration may prefer two completely different coloured tints. However, people with conditions where light is scattered in the eye (for example, cataract) often find filters that block out short wavelengths, such as yellow or amber filters, helpful.
Most optometrists and low vision providers will be happy to discuss the different tints available with you; they can sometimes also lend you a type of tint to test over a period of time. This may help you find the best tint for helping with your light sensitivity.
A special instrument, the MRC Intuitive Colorimeter, is sometimes used to determine the colour of filter that will be most helpful for a given person. This instrument is not often used for people with low vision, but is commonly used to prescribe coloured lenses for people with migraine, reading problems (eg dyslexia), or epilepsy. This is because people with these conditions often find a precise colour, which is different for each person, to be much better than general colours and help with any visual symptoms.
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