Oxnard - Port Hueneme Optometry Dr. Don Steensma 465 W. Channel Islands Blvd, Port Hueneme, CA 93041 805/486-3585
The human retina (the light sensing tissue inside the eye) has two types of light sensing cells. The "rods" supply our night time vision and are very sensitive to even very weak light. They do not see in color and the resolution is not real good so at night we see large details in black, white and grey. We do not see the fine details. The "cones" are our daytime color sensing cells which are capable of very fine resolution. In daylight we see very clearly and in color.
The genes that direct how the retina forms before birth are located on the "X" chromosome. A female develops into a female before birth because she has two "X" chromosomes. A male fetus develops into a male because he has an "X" chromosome matched with a "Y" chromosome. If the males "X" chromosome is defective he does not have a second "X" to take its place and the "cone" receptors do not develop normally resulting in abnormal color perception. Thats why color vision defects are much more common in males (5% of all males) than females (very rare). This is called Inherited Color Deficiency and can be to different degrees. In most cases the person has difficulty distinguishing between red and green. They see color, but some colors appear the same.
A female with one bad "X" chromosome is considered a carrier. Her female children have a 50% chance of getting the bad "X", so 50% would be normals and 50% would be carriers. Her male children also have a 50% chance of getting the bad "X" so 50% would be normal and 50% would be color deficient.
Some retinal and optic nerve disease can also color deficiencies. This is called Acquired Color Deficiency and it most often effects yellow-blue vision instead of red-green vision.
There are many web sites that offer color vision testing on-line, but because different computers may show colors differently they are not as reliable as testing by an eye doctor.