Blue-yellow weakness is a form of color blindness. People with color blindness are born without the ability to properly distinguish colors and assume that others are like them, so they are not aware of the disease. How are color blindness and color deficiency determined? Most examinations for color blindness and color deficiency are performed using a subjective examination, usually under brighter natural light, and are commonly performed as follows. Pseudochromatic charts, often called color blindness books, use dots of the same shade but different colors to form a number or figure that can be read in natural light at a distance of 0.5m. The color-blind book should be placed correctly during the examination, and each chart should not exceed 5 seconds. Color vision difficulties, reading errors or can not be read, in accordance with the color blindness table to confirm what belongs to the color vision abnormalities. The color bundle test is to mix different colors and shades of wool bundles together, so that the person being inspected to pick out the same color bundle with the standard bundle. This method is time-consuming, and can only be roughly qualitative not quantitative, not suitable for large area screening inspection. Color mixing tester: is nagel according to the principle of red + green = yellow, designed a spectral instrument, it can quantitatively record the amount of red and green light matching required to determine the red and green sense of abnormal, this method can be both qualitative and quantitative.