Tests for Color Vision

Color blindness or color vision deficiency is a condition affecting predominantly white males in which the eye is unable to accurately take in shades of certain colors. The largest number of sufferers have red/green color blindness, though some suffer from blue/yellow, or the even more rare true color blindness in which the person can only see in shades of black, white, and gray. Testing for color blindness is important because color is often used to indicate whether something is good (green) or is dangerous (red). Being unable to read the markings on objects can lead to accidents and unnecessary danger.

Features

• Color blindness is a misnomer meant to indicate a person's inability to see color. True color blindness, seeing in only black, white, and gray, is extremely rare. Most color-blind or, more accurately, color vision-deficient individuals are only incapable of seeing certain complementary colors such as red and green (the most common type) or blue and yellow (less common). While there is a test for red/green color blindness, there is no readily available test for blue/yellow (see Reference 1).

Causes

• The usual cause of color vision deficiency is occular. Problems with the eyes cause issues with the ability to detect ranges of color accurately. Normally, there is nothing wrong with the person's brain. However, some color blindness can be caused by brain damage. Cerebral achromatopsia is a type of color blindness in which the person cannot imagine or remember colors. A close cousin to cerebral achromatopsia is transient achromatopsia, a temporary loss of color vision due to blood flow problems in the occipital cortex (see Reference 1). The typical tests for color blindness are not meant to distinguish between whether the problem is in the eye or the brain; thus, these tests must be verified by a medical professional.

Why?

• The ability to distinguish color is important in areas where colors are used to differentiate importance. One good example is traffic signals. They are ordered traditionally as red, yellow, and green. If a person has red/green color blindness, then he cannot tell which of the lights is red or green, creating the possibility for a traffic accident. Pilots have to be able to tell if the lights on their board are red or green, since red indicates a problem.

Isihara Plates

• The creation of a common test for color blindness is credited to Shinobu Isihara, a Japanese ophthalmologist. He created the test to identify abnormalities in color vision for the military. With the assistance of a colorblind physician, he created what are now called the Isihara Plates.

  The Isihara plates are pictures created from various colored dots. The primary color is either red or green, with a number done in the opposing color. If the person has normal color vision, the number will be easily readable. However, if a deficiency is present, the patient will have problems reading the hidden number. This allows a quick, informal diagnosis of color vision deficiency; however, it is not meant to be used in lieu of diagnosis by a professional.

Isihara Updated

• The City University of London is updating the Isihara Plate concept for specific use on the Internet. The video features a colored square that moves and changes color throughout. The university has made this new test available to download online at www.city.ac.uk/avrc/colourtest.hmtl. It is 90 seconds long and the square holds a color for two to three seconds at a time.