Have you ever wondered why you might struggle to see at night, read in dim light, or drive at night? Or perhaps can never find that pair of black socks in a darkly coloured drawer? This is most likely due to the impacts of poor contrast sensitivity.
What is Contrast Sensitivity?
Contrast Sensitivity is your ability to see subtle differences in your field of vision. It allows us to determine the difference between an object on a similar colour background. For example, someone with poor contrast sensitivity may have a hard time seeing the bird in this image.
1Visual Acuity Eye Test Chart – 100% contrast
20/20 Vision does not mean perfect real-world vision
You may be lucky enough to have achieved 20/20 vision in your last eye test, which tests how well your eyes can see at a distance (visual acuity). However, that does not mean you see well or have perfect vision. Your opticians eye chart tests your visual acuity with 100% contrast – black letters on a white background.
But as you know life is not all black and white, it is full of different shades of colour, shadows, low light and glare. So having good contrast sensitivity is important for us to be able to see in many situations such as:
- Being able to tell the difference between an animal and an object at night time
- Seeing a pedestrian or cyclist on the road on a sunny day or in poor weather conditions
- Seeing the steps of a stairs or the slope of a hill before reaching it
- Stepping off footpaths or steps
- Pouring tea or coffee into a darkly coloured mug
- Reading material with poor contrast, such as a newspaper
- Distinguishing facial features on others
What causes poor contrast sensitivity?
Low contrast sensitivity can be a sign of a variety of eye disorders or conditions, such as cataracts, glaucoma and age-related macular degeneration. It can also simply be a sign of a thinning macular pigment at the back of your eye.
- Cataracts – They occur when the natural lens inside your eye becomes cloudy and yellow. Many patients with cataracts have good visual acuity but still complain of poor quality vision due to decreased contrast sensitivity. These symptoms are amplified in situations where patients experience glare, such as oncoming car headlights when driving at night. In most cases, people with cataracts notice a significant improvement in both visual acuity and contrast sensitivity after cataract surgery.
- Glaucoma – Glaucoma is a progressive eye disease that damages your optic nerves. Your optic nerves transmit visual signals to your brain, including information on colour, brightness, and contrast. This is why damage to your optic nerves can affect contrast sensitivity.
- Macular degeneration. The macula is a small area in the retina, is responsible for your central vision and seeing fine details, such as reading text in a book. The macula is protected by a protective layer called the macular pigment which is made up of three nutrients called Lutein, Meso-Zeaxanthin and Zeaxanthin. If this macular pigment is not nourished with these specific nutrients from our diet, it breaks down. This reduces the protection from blue light, oxidative stress and ageing it affords to the macula. A weakened macular pigment can lead to damage to the macula, which over time can develop into Macular degeneration causing vision loss. Patients may lose visual acuity, colour vision, and contrast sensitivity. However, most people retain normal peripheral vision.
When should you go to see an eye doctor?
If you are not happy with your eyesight, we would always recommend you make an appointment to see your eye doctor. Explain and describe the different situations you find yourself in when you are not happy with your vision.
A routine eye exam does not include contrast sensitivity testing. If your eye doctor suspects you have a contrast sensitivity problem, the most common way to check for this is using a Pelli-Robson contrast sensitivity chart.
The chart features horizontal lines of uppercase letters in the same size, where the characters fade from black to grey gradually.
This type of vision test is usually performed while you are wearing your eyeglasses or contact lenses (if you need them).
2Contrast Sensitivity Eye Test Chart