Stereopsis, also known as stereopsis and stereoacuity, is the ability of the visual organ to perceive the distance, depth, height and three-dimensional spatial position of surrounding objects. Due to the horizontal separation of the two eyes, objects are imaged in the retinas of the left and right eyes, forming a small difference in correspondence, i.e. binocular parallax, and resulting in stereoscopic vision. The acquisition of stereopsis and the fine sharpness of stereopsis depend on accurate and coordinated eye movements and macular central sulcus gaze in both eyes. Stereopsis is the ability to distinguish the smallest horizontal parallax (zero parallax) between the retinal images of the two eyes, and is measured in seconds of arc angle (“), with a normal value of 6 degrees to 10 degrees. However, with the current means of examination, the normal value is usually 40″~60 “c. The smaller the measured stereopsis sharpness of a person, the better his or her stereopsis function. The clinical classification of stereopsis according to the size of stereopsis is central macular concave stereopsis (visual acuity ≤ 60″), macular stereopsis (80″~200″) and peripheral stereopsis (400″~3000”). The absence of stereopsis is called stereopsis blindness. Stereopsis can be divided into local stereopsis (1ocal stereopis) and global stereopsis (global stereopis), local stereopsis is a small number of lines constituting parallax primitives, containing little parallax information, first in the retina by monocular cues or cue signals and other stimuli to form two-dimensional graphics, and then transmitted to the brain fusion into three-dimensional images, so local stereopsis is only a Therefore, local stereopsis is only a crude and low-level stereopsis function. The overall stereopsis is a fine and advanced stereopsis function because it is composed of a large number of parallax primitives with hidden parallax information, which contains a large amount of parallax information and directly completes the transformation of parallax information from 3D to 2D in the cerebral cortex. Factors affecting stereopsis include age, visual acuity, visual field, refractive error, and binocular inequality. A decrease in monocular vision is more likely to cause stereopsis dysfunction than a symmetrical decrease in binocular vision. One-eyed people can also judge the distance, that is by monocular cues: such as object shadows, object overlap, relative size, motion parallax and the way to observe objects and through acquired training, and binocular vision normal people’s stereo sense exists essentially different. Domestic stereopsis examination methods are divided into: distance stereopsis, middle distance stereopsis and near distance stereopsis according to the distance of examination. Far stereopsis has no set, adjustment and pupillary reflexes involved, is relatively static stereopsis; Near stereopsis has the above reflexes involved, is relatively dynamic stereopsis, and set and stereopsis are very close relationship, it provides depth information. Because the mechanisms of near and far stereopsis are different, a single stereopsis cannot be used to assess stereopsis. Modern standards for standardized stereopsis methods include three points: ① RDS must be used to detect overall stereopsis. ② Duplex determination of distance/near stereopsis must be applied. ③ 3 thresholds of zero, crossed and uncrossed parallax must be measured. The ancient stereopsis examination method is to qualitatively examine stereopsis in the natural state, such as the double pencil tip examination method: the examiner holds a pencil tip downward vertically in front of the examinee’s eyes at 33 cm, and the examinee takes another pencil tip and aligns it vertically upward to the pencil tip held by the examiner, comparing the results when both eyes look at the same time and when the eyes look at one another. There is also a foot vertical through the circle method: the examiner holds a head end wound into a diameter of 1 ~ 2mm metal circle placed in front of the examinee’s eyes, the examinee holds a front end folded into an obtuse angle of the metal wire let it through the circle, if you can successfully pass through the initial judgment that the examinee has macular central fossa stereopsis. These two methods contain monocular clues and are rarely used clinically.