A routine eye exam generally includes screening for glaucoma, macular degeneration and a standard visual acuity test on a high-contrast letter-reading chart. While these eye health tests are important to assess possible causes of eye problems, they don’t capture the “big picture”, which includes the functional consequences of eye problems; contrast sensitivity tests should be included to detect problems that affect functional vision.
As the population ages, various age-related disorders may decrease contrast sensitivity. This will affect how people can use their vision in Activities of Daily Living. Detecting obstacles in the night driving, detecting the height of a curb (and avoiding a fall and possibly a broken hip), detecting milk in a Styrofoam cup, are all activities that require adequate contrast vision.
Clinicians are generally most interested in knowing what causes a condition versus knowing the consequences of a condition for functional vision. This is why low contrast tests aren’t normally included in a routine exam. If a patient cannot see well enough, an ophthalmologist’s first reaction is to find out what causes the condition. While this is necessary for effective treatment, it is often not enough to help alleviate the consequences for functional vision.
According to August Colenbrander, M.D., an affiliate senior scientist at the San Francisco-based Smith-Kettlewell Eye Research Institute, low contrast vision screening needs to be promoted, since high contrast visual acuity tests are only a partial predictor of how well people’s vision will serve them in Activities of Daily Living (ADL). Most such activities provide less contrast than a letter chart with solid black letters on an empty white background. Threshold contrast levels, such as those measured with the Pelli-Robson chart, are also not very common.
Dr Colenbrander supports more studies and believes better – and quicker – low contrast sensitivity tests can be done using low-contrast eye charts and mixed-contrast eye charts. These cards present contrast levels that are more common in everyday tasks. The mixed-contrast eye charts, which he pioneered, have high- and low-contrast words, letters and objects side by side. Dr Colenbrander’s reasons for developing the mixed-contrast format were two-fold: time and convenience. It is considered the fastest and most demonstrative way to explain low contrast sensitivity to patients and their families.
The doctor Ask Gary adds that once low contrast sensitivity loss is diagnosed, clinicians can help patients function better by offering them a tangible solution, such as a reading lamp or a magnifier with increased illumination using LED lights. Dr Colenbrander also warns patients with low contrast sensitivity not to drive at night. For example, if a pedestrian crosses the road in front of a patient driving with low contrast sensitivity, the driver probably won’t see the pedestrian since it’s a dark-against-dark scene with very little contrast.
In the gadget-oriented society in which we live, consumers often think that we need the gadget to alleviate the consequences of a problem. In many situations, awareness of the problem is just as good as any gadget. If an elderly patient does not understand her contrast problem, she may stumble over a low-contrast curb and break a hip. If we can warn her, she will be more careful; so that this does not need to happen.
Precision Vision offers a variety of low-contrast and mixed-contrast eye charts for testing for low contrast sensitivity. Used in research as well as in general practice, the charts manufactured by Precision Vision are extremely precise. Colenbrander Mixed-Contrast Chart.
Precision Vision is continuously developing new products for fixation, acuity, contrast sensitivity testing, colour vision and several highly specialized products, as well as new features in computerized vision testing.