What is a Pupillometer
A pupillometer is a device that measures the distance between the pupils. The device is used when you order new eyeglasses. The pupillometer is used by opticians, who are experts in ordering and adjusting eyeglasses. The pupillometer accurately measures how far apart your pupils are, which ensures that your lenses are created to exactly match your eyes. If the pupillometer measurement is inaccurate, the eyeglasses may cause blurry vision or headaches. You can also easily measure your pupillary distance at home without a pupillometer.
Key takeaways
- A pupilometer is an instrument that measures the distance between the pupils.
- The pupillometer ensures that the eyeglasses prescription power is placed in the line of sight.
- If eyeglasses are made with an inaccurate pupillary distance, it can cause blurry vision and headaches.
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Understanding Pupillometer
The pupil is the small black circle in the center of the eye. It is a tiny opening that allows light to pass through the eye. The pupil can shrink or enlarge to change the amount of light that enters it. The line of sight goes through the pupils. Your pupils are where the full prescription power is located in your glasses. The pupillometer is an instrument that measures the distance between your pupils. A pupillometer is a prescription centration tool which is most beneficial for people with high nearsightedness or farsightedness, high astigmatism, or progressive lenses.
The distance between the pupils is called the “pupillary distance” or “PD”. It is measured in millimeters. When eyeglasses lenses are manufactured, the prescription power is placed where the pupils are located. It’s important for the pupillary distance (PD) measurement to be accurate if you have a high prescription power (above -3.00 DS) or high astigmatism (above -1.50 DC). With high powered glasses, the prescription can significantly change if you are not looking through the optical center of the lens. If your pupillary distance (PD) measurement is off by a few millimeters, you would be looking through the wrong prescription power. The pupillometer device ensures that your eyeglasses lenses are made accurately to match your eye’s location.
The Use Of Pupillometers
Pupillometers are used to measure the distance between the pupils, in order to accurately create eyeglasses lenses. The pupillary distance can be measured as monocular (one eye) or binocular (both eyes). The pupillary distance can also be measured for either distance or near viewing. The measurements vary based on whether you are buying single vision or progressive lenses, and if you are using the glasses for distance or near viewing.
Monocular Pupillary Distance
The monocular pupillary distance is the distance from the center of the pupil to the middle of the nose, measured in millimeters. There will be two numbers: a right eye and a left eye measurement. For example, the measurement may read 32 mm for the right eye and 30 mm for the left eye. Monocular PDs are used if you are buying progressive lenses. Progressive lenses have a distance power at the top of the lens, and gradually change to the reading power at the bottom of the lens. Progressive lenses are used by presbyopes who need help with reading.
Binocular Pupillary Distance
The binocular pupillary distance is the distance from the center of the right pupil to the center of the left pupil, measured in millimeters. This measurement is only one number. For example, the binocular PD may be 63 mm. A binocular pupillary distance is used when ordering single vision lenses. Most young people under the age of 45 use single vision lenses.
Distance Pupillary Distance
The distance pupillary distance is also known as the distance PD. It is the distance between the pupils when viewing a far target. When we are looking far away at a distance, the eyes diverge, or pull apart. The distance between the pupils is greater when we are looking far away. A distance PD is used for fabricating distance glasses, such as for nearsightedness. The pupillometer measures this value by having you look at a target that appears far away.
Near Pupillary Distance
The near pupillary distance is also known as the near PD. It is the distance between the pupils when viewing a near target. When we are looking close up, the eyes converge, or pull together. The distance between the pupils is smaller when we are looking close for tasks like reading. A near PD is used for fabricating reading glasses. The pupillometer measures this value by having you look at a target that appears to be close, within arm’s reach.
How A Pupillometer Works
A pupillometer measures the distance between the pupils by using reflections of light. You will hold up the pupillometer like binoculars and look inside of it. You will see a green light. The optician will look through the other side of the device to see your eyes. The front of the eye, known as the cornea, reflects light. The optician will use a ruler to measure how far apart your corneal light reflections are. This measurement provides the pupillary distance.
Measuring Pupillary Distance (PD) Without A Pupillometer
If you need to order glasses online, you can measure your pupillary distance with a ruler at home. Here are the steps to measuring your pupillary distance (PD) at home:
- Stand 8 inches away from a mirror.
- Hold a ruler against your eyebrow.
- Close your right eye. Align the 0 mm mark on the ruler with the center of the left pupil. The center of the left pupil is the center of the black spot in the front of the eye.
- Close your left eye and open your right eye. The millimeter mark that lines up with the center of your right pupil is your binocular PD.
