Everything you need to know about Pupillometers

A pupillometer refers to two types of medical devices, each with a different function. One of the devices measures the diameter of the pupil in the eyes. The other device measures the pupillary distance (PD), which refers to the distance between the centers of the right pupil to that of the left pupil. Unless mentioned otherwise, the devices discussed here are those used to measure pupillary distance.


A pupillometer did not exist a few decades ago. Owing to advancements in technology, we now have this modern equipment. However, these digital and automatic pupillometers were non-existent in the past. How did ophthalmologists measure pupillary distance and diameter back then? Let us look at some of the old devices used as pupillometers:

  • The Essel Pupillometer

It use was used from the 1940s to the 1990s. It consists of two metal tubes, each surrounded by plastic ends. With each tube cupped on an eye, a measurement scale determines the horizontal distance between the two pupils, thus, giving the pupillary distance.

  • Before the 1940s, pupillary diameter and distance measurements were done using rulers and calipers. Of course, these measurements were subject to a lot of human errors, making them less accurate and reliable!

Conditions tested using pupillometers

The use of pupillometers is increasing in critical neurological care and emergency care settings. Studies show that they are vital to trauma centers and make a huge impact. They can detect the presence or absence of the light reflex, which is a vital reflex that determines the extent of brain damage after sudden trauma.

Another study defines the importance of pupillometers in critical care settings, such as the intensive care unit! 

Pupillometers also assess intracranial values. A study showed that they could be used to accurately and precisely monitor intracranial pressure as it varies in correlation with the intracranial pressure. 

Types of pupillometers

  • Hand-held digital pupillometer

Portable hand-held pupillometers are currently available in the market and operate on batteries. The advantage of these pupillometers is their portability. It measures the pupillary distance (PD), cornea vertex distance (CVD), and pupillary diameter. The display in these devices is digital, giving clear and accurate results that are easy to read. This device eliminates human error, which otherwise occurs with manual pupillometers. It is useful for both binocular and monocular measurements.

The video pupillometer measures binocular refractive measurements and errors and the intensity of the mistakes. It measures refractive errors such as myopia, hypermetropia, astigmatism, among others. It is best for measuring refractive errors of uncooperative patients like babies over two months and the elderly. It is also useful in measuring pupil size and pupillary distance. It can detect whether glasses/lenses are of the right refractive intensity for a person. 

  • Hand-held Pupillometer used for measuring the pupillary size

Unlike others mentioned, this hand-held pupillometer does not measure the pupillary distance (PD). Instead, its use is in measuring the pupillary size and diameter. It does so by passing a ray of light through the pupil and notes the changes in pupil diameter after the light passes. Typically, after light passes through the eyes, the pupil diameter decreases.

This tool used in the emergency assessment of an acute brain injury as a light reflex is coordinated and controlled by the brain. The presence of the light reflex indicates normal brain functioning. However, if the light reflex is absent and pupillary diameter does not reduce with light introduced, it means there’s considerable brain damage. Its use is in triage and emergency rooms for the assessment of trauma victims like those from car accidents. 

The advantage of this pupillometer is that it's automatic and quick, so it removes any human error that could occur while reading the pupillary diameter using manual methods.

Brands of Pupillometers

  • Luneau Technology Corneal Reflex Pupillometer PM 110

This pupillometer uses corneal reflection in measuring pupillary distance. It is a hand-held automatic pupillometer that gives off light when the instrument is picked and automatically shuts off the light when put down. It measures both monocular and binocular pupillary distance, with its readings correct to the nearest 0.5 mm. 

The range of monocular and binocular pupillary readings for this device is 48 mm to 77 mm. 

  • Adaptica 2WIN

Adaptica 2WIN is a binocular refractor and a vision analyzer. It measures vision refractive errors like hypermetropia, myopia, astigmatism, and other such errors and gives a precise measurement for spectacle lenses. It’s a portable video pupillometer that has an ergonomic design. 

  • US Ophthalmic

The US Ophthalmic Pupillometer (Ezer) is one of the most widely used pupillometers as it also measures vertex distance! The pupillometer also measures pupillary distance accurately. It is excellent for both monocular and binocular measurements. Binocular measurements range from 44 mm to 83 mm, and the monocular sizes range from 22 mm to 41.5 mm. The LED light can be adjusted to give different light intensities. It’s lightweight and easy to use.


The NIDEK pupillometer measures pupillary distance and gives great accuracy to the nearest 0.25 mm. It has a stable and ergonomic design to ensure there is the least possible movement during the measurement. Moreover, it’s lightweight and easy to use. 

  • Haag-Streit Diagnostics Lenstar LS 900

This multipurpose device is useful with many other functions other than pupillometry. Other parts include measurement of corneal thickness, anterior chamber depth, and lens thickness. 

The software comes with a portable scanning device. The device takes quick scans to ensure they are as reliable and accurate as possible. This device ensures the least movement is detected in the scans!

  • Schwind

The SCHWIND SIRIUS topography and pachymetry equipment has a camera attached to software that enables rapid and accurate measurements. It measures the size of the pupil and its changes with the corneal light reflex! It has an ergonomic design.

  • Reichert Technologies – Reichert PDM Digital PD Meter

This portable digital device is for both binocular and monocular measurements. It offers effective pupillary distance measurements accurate to the nearest 0.5 mm. For binocular measurements, it ranges from 46 mm to 82 mm, while for monocular measurements, it is a range from 23 mm to 41 mm.

The pupillometer has an ergonomic design so that it easily and comfortably fits in the palm without slipping. It uses the corneal light reflection method to measure pupillary distance. The pupillometer has a long battery life, and you can adjust to switching off automatically after one minute of no use, which extends battery life. The LCD provides an output that is easy to read. 

  • NeurOptics NPi-200 Pupillometer

The NeurOptics pupillometer automatically measures the size of the pupil without having any external variables influencing the measurements. It enables the tracking of pupillary size changes over time, which means one can keep track of the pupillary diameter. It uses an infrared camera and an LED light source. The pupillometer has an ergonomic design that fits perfectly in the palm and does not slip. Moreover, the device comes equipped with Bluetooth.

  • Huanyu Digital Pupillometer (LY-9C)

This device is excellent for binocular measurements. It has a viewing distance that’s adjustable from 30 cm onwards. Its binocular measurement range is from 50 mm to 80 mm. Monocular size is also available in the range of 25 mm to 40 mm.

Most Common Specifications for Pupillometers

Pupillometers most commonly are both monocular and binocular. And they typically have a measurement ranging from 40 mm to roughly 90 mm (binocularly). Other than that, they are usually hand-held devices that use Infrared waves. Digital infrared pupillometers are the most commonly used pupillometers. 

Alternative Equipment

A pupil gauge or ruler serves as an alternative in the measurement of pupillary size and distance. However, the results are inaccurate and prone to human error when compared to pupillometers!

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