Loss of color vision refers to an insensitivity to the ability to discriminate one or some colors. According to the doctrine of the three primary colors, loss of color discrimination of one color is called dichromatic vision, and loss of red color discrimination is called red-blindness. Such a person has a shortened red end of the spectrum, is less sensitive to the red color of the spectrum, and sees it as dark. He drives through red lights, often because the red light is not bright enough for him. Here’s how to diagnose color vision loss. The pseudo-identical color chart is usually called the color blindness checklist, and there are Shinobu Ishihara and Stilling pseudo-identical color charts in foreign countries and Yu Zhibing and Jia Yongyuan color blindness check charts in China. The design principle is that the pictures are made up of dots of the same lightness and darkness (shades of hue) but different colors, and each picture is made up of numbers, letters, patterns or curves with dots of one color, and the bottom of the picture with dots of several other colors. Normal people can make correct judgments because they recognize pictures by color but not by brightness, while people with abnormal color vision recognize them by brightness but not by color, so they cannot make correct judgments. Another kind of picture is composed of dots with the same color but different lightness and darkness, which normal people cannot recognize, but color vision abnormal people can recognize. Currently, this method is still used as a screening tool to separate normal people from those with abnormal color vision. Fornsworth-munsell-100 color tester consists of 93 color discs of different wavelengths (wavelength 455-633nm), divided into four wooden boxes, each box has a fixed color disc at each end, as a color matching use, the rest of the color discs can be moved. The inspection method is under the fixed illumination, asked to be examined according to the law of color change, sequential arrangement of color discs, each box limited to 2min, the number on the back of the row of boxes recorded on the record sheet, and score for the graph. The graph for normal eyes is a circular graph close to the inner circle; for those who are not normal, the graph is shifted outward in a cogwheel shape in the difficult part of color discrimination. FM-100 color test can be used for color vision abnormalities and quantitative analysis. The inspection apparatus is 15 color markers in a box, the inspection method is basically the same as above, requiring 15 color markers to be arranged within 2min. Judgment of the results, such as 1 to 15 color coding all correct or two adjacent color coding before and after the order reversed for through; such as the order of confusion for failure. The results are plotted into a chart to determine whether there are abnormalities in color vision. This test method is simple, high precision, and can determine the type and degree of color vision abnormalities. The color vision mirror is a spectral instrument designed according to the principle that red light and green light are properly mixed into yellow light. The lower half of the circular field of view from the eyepiece is yellow light, and the upper half is a mixture of adjustable red light and green light.