What you and I see may differ - are you aware that we don’t all share the same visual perception of color? Between eight and ten percent of men (but very few women) have some degree of color blindness. I suspect that we all know someone with this condition. Recently, a patient explained to me that he couldn’t see the difference between a green and a red traffic light. He immediately reassured me that from an early age he learned a simple trick: the red light is always on top!
How do we see colors? Think of the eye as a camera. In front is a lens that focuses images onto the retina, located at the back of the eye. The retina contains photoreceptors, which are shaped like rods or cones. They contain pigments that change when light strikes them. Just as a painter can mix a small number of colors together to make up every color and shade, when rods and cones work together, the eye can see millions of colors.
Color blindness is a condition where colors cannot be clearly distinguished. The name is misleading, because those with color blindness are certainly not blind. It can range from mild to severe. This problem can be life changing, and may make it harder to read and to learn. However, children and adults are usually able to adapt.
Most problems with color vision are inherited and present at birth. This type of color blindness doesn’t change with time, and occurs when cone cell types are missing or don’t work properly. There are different types of color blindness. Red/green color blindness is the most common. A much more rare form is blue-yellow color blindness (which is actually the inability to distinguish between blue and green; and yellow and violet!). Some young children have blue/green confusion, but this actually improves with age. The most rare type of color blindness is the total inability to distinguish colors, or monochromacy. It affects only about 1 in 33,000 people in the United States. Those with this condition see the world in shades of gray, have poor clearness of vision, and are extremely sensitive to light.
Occasionally, color blindness is not inherited, but acquired:
•Chronic illnesses that may limit color perception include Alzheimer's disease, diabetes, glaucoma, leukemia, liver disease, alcoholism, macular degeneration, multiple sclerosis, Parkinson's disease, and sickle cell anemia.
•Accidents or strokes can damage the retina or affect particular areas of the brain or eye.
•Some medications can affect color vision. These include antibiotics, barbiturates, anti-tuberculosis drugs, high blood pressure medications, and some psychiatric medications.
•Certain industrial or environmental chemicals, including carbon monoxide, carbon disulfide, fertilizers, styrene, and some chemicals containing lead, can affect color vision.
How is color blindness diagnosed? There are several tests. The most common is a series of circles filled with dots of different sizes and colors. A person with normal color vision sees a shape that, due to its color, clearly stands out.
There is no cure for inherited color blindness, and it cannot be prevented. If the cause is an acquired disease, accident, medication, or chemical, treating the cause may help, and some do improve over time. More often, however, the damage is permanent.
Most people compensate well, relying on shades and position cues that most of us don’t notice. There are lenses and visual aids that may help. If color vision may be a problem for you, “see” your primary care doctor, optometrist or ophthalmologist.
Dr. Alan Frischer is former chief of staff and former chief of medicine at Downey Regional Medical Center. Write to him in care of this newspaper at 8301 E. Florence Ave., Suite 100,
Downey, CA 90240.