Correct wearing of glasses depends on the selection of lenses and frames. Interpupillary distance allows you to determine the centering of the lenses relative to the patient's pupils. To do this, the doctor determines the distance, enters the data in the prescription. Measurements can be taken at home on your own, but the accuracy of the result will be higher with an ophthalmologist.
What is interpupillary distance
While wearing glasses, some people complain of headaches, feeling unwell, eye pain, dizziness. The glasses may not fit for the following reasons:
- violation of length between lens centers;
- facial asymmetry;
- vertex distance selection;
- Wrong glasses.
Determination of interpupillary distance avoids some problems. The doctor enters the indicators in the prescription, when selecting glasses, the pharmacist will pay attention to the center of the lens coincides with the center of the pupil.
Interpupillary distance - the gap between the pupils. Pupils can be located asymmetrically, so ophthalmologiststhere is a concept of binocular and monocular gap:
- Monocular distance is measured from the center of the bridge of the nose to the center of the pupil.
- Binocular - the segment between the pupils. The binocular distance is equal to the sum of the monocular measurements.
In adults, indicators rarely change over time, in children, as they grow, new glasses should be selected.
Normal indicators
The definition of interpupillary distance has changed. The rules have changed a bit. The method of measuring the center-to-center gap has changed, taking into account past mistakes.
Previously, the difference in the gap was determined by 2 mm for distance and near. Now this figure varies from 4 to 6 mm. The distance can be written in any number, and according to the old standards, the indicator should be even. The new recipes are different from the old ones. Thus, the distance was indicated separately for distant and separately for close objects with a difference of 2 mm. Now it is considered that the indicators can differ up to 7 mm. Modern lenses of complex design determine for close distance 2.5 mm less for each eye than for far distance.
The normal interpupillary distance is 62 mm, the data can be in the range of 54-74 mm. If the segment turned out to be fractional, then the result is rounded off. With strabismus, the prescription indicates the distance that a person would normally have.
Can I measure myself
You can measure the interpupillary distance yourself. This will require a millimeterruler and mirror. If there is no ruler, then you can print a special scale for measuring, but first you should make sure that the printer does not distort the scale.
The room should be well lit. You should stand in front of the mirror at a distance of 20 cm. The ruler should be located above the eyeballs, parallel to the line of the eyebrows. Keep your head straight to get more accurate measurements.
First, close one eye and place zero on the ruler opposite the center of the left pupil. The more accurately the center is determined, the better the result will be.
Next, you should open the second eye and find the division on the ruler, which will be exactly in the middle of the pupil. At this time, you can not move your head or move the ruler. The eyes must be directed to the mirror in order for the measurement to pass correctly. The data obtained in millimeters is the interpupillary distance. Measurements should be taken 3 or 4 times.
Helping another person
You can take measurements with the help of another person. By following simple rules, you can understand how to measure interpupillary distance with an assistant. To do this, you need to stand opposite each other. The distance between faces should be 20 cm. Larger or smaller intervals will distort the result.
The person being measured should look over the assistant's head. It is desirable that the head be lower than the subject's eyes. You should look at an object that is 3–6 meters from a person.
For measurement accuracyyou can not move, move your head and rotate your eyes. The gaze must be fixed. The ruler should be placed above the eyes parallel to the line of the eyebrows. Zero should be set in the center of the pupil of one eye and determine at what distance the other pupil will be.
Check with an optometrist
Measurement of interpupillary distance by an ophthalmologist will show a more accurate result. When choosing glasses, the doctor holds a special ruler at different intervals, depending on the degree of myopia or hyperopia.
If the patient suffers from farsightedness, then the distance from the ruler will be 33 cm. The patient should look just above the ruler at the doctor's forehead. The ophthalmologist closes one eye and looks at the patient's opposite eye with the other. Thus, the doctor fixes the edge of the limbus. Similar actions are carried out with the other eye. The zero division, corresponding to the rim of the patient's eye, will become the distance between the pupils.
With myopia, the patient looks at an object that is located at a distance of 5 meters from him. A special ruler will fix the zero division opposite the cornea of the left eye and the right one. The result obtained will show the space between the pupils. A similar device can be used at home, the instructions are attached to it.
Pupillometer
Pupillometer is used to determine the diameter of the pupils, and the distance between them. It is used by ophthalmologists. The modern device is rich in settings and guarantees high accuracy of the result. Comparedwith other methods, pupillometer has advantages:
- quick accurate result;
- define each eye;
- accuracy is not affected by uncontrolled pupil movements and room lighting;
- the result is displayed on the display of the device.
The device is capable of taking measurements from the bridge of the nose to each pupil. Shows data for asymmetry, farsightedness and myopia. Pupillometer has contraindications:
- Deviated septum.
- Severe visual impairment.
- Wryneck.
The ability to measure the distance between the pupils helps to adjust the interpupillary distance when using optical devices. Some require adjustment to see the image.
Adjusting the interpupillary distance
Optical instruments such as binoculars or a microscope with 2 eyepieces require additional image adjustment. Initially, you should adjust the sharpness and align the device horizontally. When observing through the lenses, it is necessary to reduce the binoculars to adjust the interpupillary distance. The image should become one.
For complex digital devices, you can initially set this distance and complete the image. With the right indicators, it will be comfortable to use the device. The distance between the centers of the lenses must match the interpupillary distance.
