What Is Pupillary Distance?
Interpupillary distance is simply the distance of the pupil. A normal person looks at the same object with both eyes, and the objects are imaged at the retinas of the two eyes and overlap in the visual center of the brain to form a complete, three-dimensional, single object. This function is called binocular monovision. However, infants and young children are easily affected by external factors during the formation of binocular monoopia, which causes one eye to stare at the target and the other eye to deviate from the same target, so strabismus occurs. Medically, the eyes are squinting inwardly when looking at an object, which is called esotropia, which is commonly known as "cross-eying."
Interpupillary distance
Interpupillary distance is simply the distance of the pupil. A normal person looks at the same object with both eyes, and the objects are imaged at the retinas of the two eyes and overlap in the visual center of the brain to become a complete, three-dimensional single object.
In short, the pupillary distance is the pupil distance. The English name is Pupil Distance, which is abbreviated as PD in optometry prescriptions and the unit is mm.
Wear
Interpupillary distance measurement in special cases
1.The size of both pupils varies
The distance from the inner and outer edges of the right pupil to the outer and inner edges of the left pupil can be measured separately, and then taken twice
The eyes of the examiner and the patient should always be at the same height during the measurement.
Do not touch the affected eye
With glasses, you must not only measure the refractive power, but also measure the interpupillary distance. For corrective glasses with slightly larger diopters, if the interpupillary distance is significantly wrong, even if the diopters meet the requirements, they will feel uncomfortable and even unbearable because the eye muscle balance of the two eyes is damaged. As long as the light received by the visual axis of one eye does not enter through the optical center of the lens, the prism effect of the lens refracts and changes the direction of the light entering the eye. The image formed in this eye does not fall on the other eye At the corresponding point, this will immediately cause double vision, of course Interpupillary distance
This is unbearable for a moment, so the brain immediately generates corrective reflexes, adjusts the extraocular muscles, so that the effects received by both eyes still fall on their corresponding points, instantly avoiding double vision, but often makes people feel It is very difficult and uncomfortable. The greater the degree of correction, the more uncomfortable it is. Different people have different tolerances to the correction amount. Generally, the tolerance to the correction in the horizontal direction is greater, especially the correction tolerance that requires strengthening the role of the medial rectus muscle. Extremely limited. The two eyes are generally high but the optical center of the eyes is not generally high, which is easily unbearable. A few people even have strabismus head positions to help overcome the lack of longitudinal correction. Therefore, it is necessary to make the paired glasses not only have the right degree and the correct interpupillary distance, but also the optical center height is in line with the actual situation of the eyes of the wearer. The eyes of a few people are not on the same level, so you should indicate which eye is higher and the height difference between the two eyes. In addition, the distance between the two eyes of the individual and the center line of the nose is obviously not the same. It should also be measured and noted so as to take special care when processing optics. Computer optometry can generally reflect the interpupillary distance when looking far away. If the eyes of each subject are looking at the fixation target in the machine when detecting the refractive power of the two eyes separately, when the first eye is checked and the machine is moved to the second eye, the subject should not have any problems in the head. The measured interpupillary distance should be considered accurate when looking far away, regardless of whether the visual axis of the eye passes through the center of its pupil, or whether its pupil is centered, does not affect the accuracy of this data. If this data is used for spectacles that take into account both distance and distance, only 1mm needs to be subtracted; for spectacles such as old glasses, 2mm is generally required to be subtracted; a few special close-knit workers have working distances as close to 20cm , Or even closer, you need to subtract 3-4mm. People's eye distance is not fixed, and the pupillary distance of glasses is generally relatively correct. As mentioned earlier, people have a considerable degree of correction ability in maintaining eye muscle balance in different states. Within this range, correction of eye muscle balance does not cause or cause eye fatigue in a short period of time. If you experience eye fatigue for a long time, after understanding the characteristics of the posture at that time, you may wish to try a prism to clarify how the pupil distance needs to be modified in this particular posture. A small number of people suffer from eye fatigue caused by improper refractive correction, poor eye posture, poor lighting, or abnormally poor regulation, and so need to be adjusted or corrected accordingly. The light-shifting method can only be applied to high-power glasses.
