Blue and yellow colour deficiency is one less common form of this condition. A more serious case of colour blindness, although extremely rare, only lets people see shades of grey. These colour blind people cannot see any colour at all, and their world has the appearance of a black and white movie. Colour deficiency is usually caused by a speci-fic gene, but can also result from damage to the retina. The genetic condition, which cannot be cured, is present in more men than women.
Owls have the largest eyes of any species.
If our eyes were proportional to that of an owl, our eyeballs would be the size of grapefruits and weigh 5 pounds each. FYI is a quarterly publication of the Canadian Association of Optometrists .