The pupillary distance refers to the distance between the center of the pupils when the two eyes face the front and the line of sight is parallel. Generally expressed in English letters “PD”, the unit is mm.
Classification of pupil distance
Binocular PD and monocular PD
Monocular PD: The distance from the center of the right (left) eye pupil to the midline of the nasal bridge (applies to monocular, squint, and gradient mirror fitting). This type of measurement will be between 20-40 mm
Far PD/Distance PD and Near PD
Far PD/Distance PD: The distance between the centers of the pupils of the two eyes when the eyes are looking into the infinity.
Near PD: The distance between the pupil centers when reading 30~40cm reading in front of eyes or working at close quarters.
Sometimes PD will be written as PD = 33/34.5, which means the distances between the nose and the center of the two pupils. In this case, PD = 33 + 34.5 = 67.5, so you can fill in 67 or 68. Only 1 mm or 2 mm will have no effect at all.
Sometimes there is a Far PD/Distance PD or Near PD. If you are shortsighted, please fill in Far PD/Distance PD. If you need a reader, please fill in Near PD.
What to pay attention to in offline optometry measurement PD？
The eye position PD is the distance between the two pupils. The normal value for males is 60.9±0.18mm, and the normal value for females is 58.3±0.13mm. Interpupillary distance is a more important parameter when fitting glasses, because the optical center is at the pupil position when glasses are fitted. Only after measuring the position of the optical center can more suitable glasses be matched, and the pupil can be located in the optical center of the lens, so as to achieve the effect of correcting vision. .
Interpupillary distance measurement can be measured with a computer refractometer, or it can be measured manually, that is, with a ruler. After measuring the interpupillary distance, optometry is also required. The purpose is to measure the refraction of the eye and check whether the patient is nearsighted, farsighted, or astigmatic, as well as the degree of eye change. After the accurate value is obtained through the eye examination, the appropriate frame and lens can be selected according to the patient’s face shape and interpupillary distance, so as to match the more comfortable and beautiful glasses, and the glasses are not easy to fatigue.
Generally, there is a certain difference between the interpupillary distance when looking at the distance and the interpupillary distance when looking at the near place. When the patient looks at the near place, the eyeball will be cohesive, and the interpupillary distance will be reduced by 2-3mm. Therefore, the interpupillary distance should be appropriately reduced by about 2mm when wearing reading glasses.
Optometry requires accurate measurement of the pupillary distance. If there is a deviation, the patient may easily experience blurred vision after wearing glasses, and even have symptoms such as headache, eye swelling, and nausea. Therefore, doctors should measure the pupillary distance accurately.
· The average PD is 60-66 mm, and about 97% of people have a PD of 54-74 mm. So if you measure a PD value outside 54-74 mm, you may have made a measurement error.
· In most cases, the female standard pupil distance is 52-65 mm, and the male standard pupil distance is 58-71 mm.
· When the pupil distance is not an integer (for example, 58.5), myopia please choose 59; hyperopia / presbyopia please choose 58.