In addition to the prescription of glasses, there is another very important data, that is, the interpupillary distance, which is the distance between the centers of the two pupils. If the interpupillary distance is incorrect, not only will there be uncomfortable symptoms such as dizziness, but in severe cases, diplopia will also occur, seriously affecting vision, and may even cause strabismus. So how to measure the interpupillary distance? First of all, there are many types of interpupillary distance, such as single-eye interpupillary distance, double-eye interpupillary distance; distance interpupillary distance, near interpupillary distance, squint interpupillary distance, etc. So what are the differences? And how to measure it? Woolen cloth?
1. Interpupillary distance: refers to the distance from the center of the pupil of the right eye to the center of the pupil of the left eye. This cohabitation is also the simplest to measure, just measure the distance between the centers of the two pupils.
2. Monocular interpupillary distance: refers to the distance from the pupil center of the right or left eye to the midline of the bridge of the nose. Those with one eye or strabismus, especially those who need progressive multifocal lenses, need to measure the interpupillary distance of one eye.
How to measure the interpupillary distance of one eye:
(1) The examiner and the patient face each other 40cm apart, so that their eyesight is at the same height.
(2) The examiner should measure from the center of the pupil of a certain eye to the midline of the bridge of the nose to obtain the interpupillary distance of one eye. (3) Accurate single-eye interpupillary distance measurement requires the use of a pupillary distance meter.
3. Distance interpupillary distance: refers to the interpupillary distance when the patient looks far away, that is, the distance between the centers of the pupils of the two eyes when the eyes look straight at infinity.
How to measure distance interpupillary distance:
(1) The examiner and the patient face each other 40cm apart, so that their eyesight is at the same height.
(2) The examiner holds the interpupillary distance ruler or ruler with the thumb and index finger of his right hand, and rests the other fingers on the patient's cheek. Then he places the interpupillary distance ruler at the lowest point of the bridge of the nose and tilts it slightly along the angle of the nose bridge. (3) The examiner closes his right eye and asks the patient's right eye to look at the examiner's left eye. While the examiner's left eye looks at the patient's right eye, the examiner aligns the "zero position" of the interpupillary ruler with the pupil center of the patient's right eye.
(4) The examiner opens his right eye and closes his left eye, and asks the patient's left eye to look at the examiner's right eye. The examiner accurately reads the value of the interpupillary distance ruler at the center of the pupil of the patient's left eye while his right eye looks at the patient's left eye.
(5) The examiner repeats step (3) to confirm whether the "zero position" of the interpupillary scale is aligned with the center of the patient's right pupil. If it is accurate, the value read in step (4) is the patient's interpupillary distance.
4. Near interpupillary distance (NCD): refers to the distance between the centers of the pupils when the patient is looking at a near target, that is, 30 to 40 cm in front of the eyes when reading or working at close range. The near interpupillary distance is always smaller than the far interpupillary distance. Measurement method of near interpupillary distance:
(1) The examiner and the patient face each other 40cm apart, so that their eyesight is at the same height.
(2) The examiner holds the interpupillary distance ruler or ruler with the thumb and index finger of his right hand, and rests the other fingers on the patient's cheek. Then he places the interpupillary distance ruler at the lowest point of the bridge of the nose and tilts it slightly along the angle of the nose bridge. (3) The examiner closes his right eye, asks the patient to gaze at his left eye, and uses his left eye gaze to align the "zero position" of the interpupillary ruler with the pupil center of the patient's right eye.
(4) The examiner opens the right eye and still asks the patient to continue looking at the left eye, and uses the right eye to read the value on the center of the pupil of the patient's left eye.
(5) Repeat steps (3) ~ (4) three times, and take the average value as the near interpupillary distance.
5. Measurement of interpupillary distance of strabismus eyes
(1) The examiner and the patient face each other 40cm apart, so that their eyesight is at the same height.
(2) The examiner holds the interpupillary distance ruler or ruler with the thumb and index finger of his right hand, and rests the other fingers on the patient's cheek. Then he places the interpupillary distance ruler at the lowest point of the bridge of the nose and tilts it slightly along the angle of the nose bridge. (3) The examiner closes his right eye and asks the patient's right eye to look at the examiner's left eye. The examiner covers the patient's left eye with his left hand and aligns the "zero position" of the interpupillary ruler with the pupil center of the patient's right eye.
(4) The examiner opens his right eye and closes his left eye, and asks the patient's left eye to look at the examiner's right eye. The examiner covers the patient's right eye with his left hand and reads the value of the interpupillary distance scale at the center of the pupil of the patient's left eye. This is the interpupillary distance of the patient.
6. Measurement of interpupillary distance under other circumstances
(1) The two pupils are unequal in size: measure the distance from the inner edge and outer edge of the right pupil to the outer edge and inner edge of the left pupil respectively, and then take the average of the two readings.
(2) The position of the two pupils is asymmetric: that is, the pupils of one or both eyes are not at the center of the iris. This is more common after trauma or cataract surgery in the elderly. The interpupillary distance is difficult to measure. You can try on glasses to determine its value. The above is the introduction and measurement methods of 6 types of interpupillary distance. More online glasses blogs about fashion glasses on Vooglam's blog.

Measures the distance between each pupil and the center of the bridge of the nose, providing a separate measurement for each eye. This helps ensure that the optical center of each lens aligns correctly with the corresponding eye. Determines the distance between the centers of the pupils when both eyes are considered together. It is essential for aligning the optical centers of eyeglass lenses accurately with the midpoint between the eyes. Get More Info