What is Contrast Sensitivity?
Contrast sensitivity is the ability of your eyes to distinguish between an object and the background. Contrast sensitivity differs from visual acuity, which measures how clear your vision is.
High contrast objects, such as white text on a black paper, are easy to see. Low contrast objects are more difficult to detect, such as a gray car on a cloudy day.
Contrast sensitivity plays a large role in the ability to safely perform activities, like walking down stairs and driving at night. Contrast sensitivity is affected by eye conditions such as cataracts and glaucoma. An eye doctor can test your contrast sensitivity and see if it is reduced from normal levels.
Key Takeaways
- Contrast sensitivity is the ability to distinguish between an object and the background.
- Common situations that require good contrast sensitivity include walking on curbs and stairs, driving at night, and seeing pedestrians in foggy or rainy weather.
- Eye conditions such as cataracts and glaucoma can cause loss of contrast sensitivity.
Understanding Contract Sensitivity
Contrast sensitivity helps differentiate between an object and its background. Something has “high contrast” when it can be easily distinguished from its background. For example, bold black letters against a white paper are high contrast. Objects are said to have a “low contrast” when it’s hard to tell between the object and its background. For example, reading a gray letter on a gray paper is low contrast.
Having good contrast sensitivity is essential to visual functioning, especially in low-light conditions. Everyday situations that require contrast sensitivity include:
- Driving at night, in rain, or fog
- Seeing pedestrians or animals when driving
- Walking down curbs or stairs
- Locating objects against similar colored background
- Distinguishing people’s facial expressions
Contrast sensitivity is different from visual acuity. Visual acuity measures how clear the vision is. For example, “20/20 vision” indicates a good visual acuity and good identification of small details. However, it’s possible to have good visual acuity but poor contrast sensitivity. Poor contrast sensitivity can make it harder to see, especially at night or on a cloudy day. People with poor contrast sensitivity might be able to see an object in bright light, but they would have a hard time seeing the same object in dim lighting.
Symptoms of Reduced Contrast Sensitivity
A reduced contrast sensitivity can make it harder for the eyes to function. It especially causes difficulty seeing in low lighting situations. Navigating around the outside world, like taking public transportation or driving in unfamiliar places, can become difficult. Symptoms of poor contrast sensitivity include:
- Difficulty driving at night
- Takes time to find objects in the dark
- Hard to see curbs or steps
- Need to use bright lighting to see things better
An eye exam is the best way to determine if there is reduced contrast sensitivity. The eye doctor can use contrast sensitivity tests, such as Mars or Pelli Robson, to accurately measure your contrast sensitivity function.
What is a Contrast Sensitivity Test?
If you have trouble seeing in the dark or at night, an eye doctor can measure your contrast sensitivity. There are two main contrast sensitivity tests that an eye doctor uses: Mars Test and Pelli Robson Test. Both contrast sensitivity charts work in similar ways. The patient is instructed to read across a row of letters, which go from high contrast to low contrast. The eye doctor counts how many letters the patient is able to see. The score will be compared to the average value to check if the patient’s contrast sensitivity is reduced.
What is Normal Contrast Sensitivity?
Contrast sensitivity is measured in log units. It can be measured in either Weber units or Michaelson units. A low score indicates reduced contrast sensitivity.
- Normal contrast sensitivity: > 1.7 log
- Mild loss of contrast sensitivity: 1.4 to 1.6 log
- Moderate loss of contrast sensitivity: 1.1 to 1.3 log
- Severe loss of contrast sensitivity: 0.8 to 1.0 log
What Affects Contrast Sensitivity?
Many conditions can reduce contrast sensitivity. Examples of eye conditions that cause reduced contrast sensitivity include:
Cataracts
A cataract is an age-related condition that typically starts in the 50s or 60s. The natural lens inside the eye becomes cloudy and yellow. The vision becomes hazy, like looking through a dirty window. Cataracts make it harder to detect low contrast objects. People with cataracts have reduced contrast sensitivity.
Glaucoma
Glaucoma is an eye disease that damages the optic nerve, which connects the eye to the brain. The optic nerve has specialized cells which transmit visual signals to your brain, including information about an object’s brightness and contrast. When the optic nerve becomes damaged, it can decrease the contrast sensitivity.
Optic Neuropathy
Other diseases that can damage your optic nerve include multiple sclerosis, sarcoidosis, syphilis, lupus, and other infectious or inflammatory medical conditions.
Macular Degeneration
Macular degeneration is an age-related eye condition. The macula is responsible for central vision and seeing sharp details. When macular degeneration occurs, the macula cannot detect contrast as well.
Treatments for Contrast Sensitivity
If contrast sensitivity is reduced, there are aids which can help someone detect low contrast objects better. Tools which assist with contrast sensitivity are:
- Brown and amber colored tinted lenses: Having tinted sunglasses can increase contrast. The brown tinted lenses can be used indoors or outdoors. They help by filtering out more light.
- Using better lighting: Objects will be much easier to see in bright lighting. People with low contrast sensitivity can use lamps to create good illumination in their homes. Tools like illuminated magnifiers or LED reading lights can help.
- Anti-reflective coatings: This coating can be applied to eyeglass lenses to reduce glare. It is useful for night driving, because headlights cause uncomfortable glare.
- Cataract surgery: If the vision is severely impacted by cataracts, the best way to improve the vision is through cataract surgery.
