The purpose of red and green test: to ensure that every step of optometry is not overcorrected.

   Ensure that the diameter of the green diffusion circle formed by red light and green light on the retina is similar to that of the red diffusion circle, the light dispersion is similar, and the brightness is similar, that is, ensure that the visual mark in red is clear or that the visual mark in red is as clear as that in green.

Principle:

   Using the chromatic aberration of the ocular refractive system and the different refraction angles of monochromatic light in the eye, when the subject has normal color discrimination and the best vision, the yellow light falls on the retina, the red light focuses equidistantly behind the yellow light, and the green light focuses equidistantly in front of the yellow light

   a. The principle that the red internal vision mark is clearer than the green internal vision mark: the green light is focused first and then divergent, forming a large dispersion circle on the retina, and the light dispersion is darker. The red light is located on the retina or the focus is closer to the retina than the green light, the light is concentrated, the diffusion circle is small, and it is relatively bright. Therefore, when the myopia diopter is slightly undercorrected, the red light is located on the retina or the focus is closer to the retina than the green light. At this time, the red internal visual mark is clearer than the green internal visual mark.

   b. The principle that the red internal vision scale is as clear as the green internal vision scale: the green dispersion circle formed by the red light and green light on the retina is directly similar to the red dispersion circle, the light dispersion is similar, and the brightness is similar. Therefore, when the myopia diopter is just corrected, the red internal vision scale is as clear as the green internal vision scale.

   c. The principle that the red internal vision mark is less clear than the green internal vision mark: the red light is far away from the retina, while the green light is on the retina or the focus is closer to the retina than the red light. The dispersion circle formed by the green light is small and the light is brighter. Therefore, when the myopia diopter is corrected, the red light is behind the retina or the focus is farther away from the retina than the green light, while the green light is on the retina or the focus is closer to the retina than the red light, Therefore, when myopia diopter is over corrected, the red internal vision scale is not clear than the green internal vision scale.