The technology

NPi-200 (Neuroptics) is a handheld automated pupillometer that includes a camera and a colour touch screen. It provides precise, accurate and objective measurements of pupil size and pupillary light reflex (PLR), as well as other parameters including minimal pupil diameter, percentage change in pupil size and constriction velocity, and displays a video of the constriction response. Measurement takes around 3 seconds per eye. The NPi-200 is used with a disposable SmartGuard. The SmartGuard positions the NPi-200 at a consistent distance to perform the scan. SmartGuard is a single-patient-use device with smart-card technology that can store patient data for each patient for the length of their admission. The SmartGuard has an radio-frequency identification memory tag that can store up to 168 paired pupil measurements, which can be uploaded to the person's electronic medical record or downloaded to a computer for research purposes.

The SmartGuard reader is required for integrating the data into electronic medical records. A barcode scanner is available to avoid manual input of patient data.


The company claims that, unlike manual PLR assessment, the NPi-200 expresses PLR in a numerical readout using the 'neurological pupil index' (NPi). The NPi is a proprietary index that is a numerical expression of the PLR on a scale from 0 to 4.9, where an NPi of 3 or higher is considered a healthy response. NPi was validated based on data from over 600,000 people with normal pupillary light reflexes. This allows an objective measurement to be taken so that, like other vital signs, changes from baseline can be recorded over time. The company also claims that a reduction in NPi of more than 0.7 can be used to predict neurological deterioration several hours before a person develops symptoms. A difference in NPi of 0.7 or more between pupils may be considered abnormal (anisocoria). The company claims that the early warning has a substantial unquantifiable benefit because it allows people to be treated earlier.

Current care pathway

Pupillary reactions are usually checked manually using a pen torch, which can lead to inter- and intra-observer variability. Pupil size is recorded in millimetres (1 mm to 9 mm) before light stimulus. Size charts are available, often printed on the side of the pen torch. To assess the PLR, the ambient light is dimmed and the person is asked to fixate on a distant target. The right eye is illuminated from the right side and the left from the left side. Direct pupillary response (the pupil constricts when the light is shone on to it) and a consensual response (the other pupil also constricts) is noted. Pupil size is measured, ideally with reference to a neurological observation chart. PLR is subjectively classed as brisk, sluggish or non-reactive.

A clinical expert said that it is often difficult to adequately dim the ambient light in the intensive therapy unit and people who are critically ill are usually unable to comply with requests to fixate on a distant target. Pen torch assessments are performed regularly by nurses as part of routine neurological assessments, and intermittently by junior doctors to confirm findings. Minimal training is required to use the pen torch, but experience is essential to accurately judge the speed of pupillary response and presence or absence of anisocoria.

The following publications have been identified as relevant to this care pathway:

Population, setting and intended user

NPi-200 is indicated for use in the clinical management of children and adults in critical care, specifically in neuro critical care, cardiac critical care, paediatric critical care and stroke units. The company states that it is important to establish a baseline reading as soon as possible for all critically ill people and that people at risk of neurological decline should be continually monitored.

The technology is used by clinicians and intensivists, in relevant tertiary settings. Because of their learned experiences across multiple disciplines, the technology is now becoming nurse-led in many locations.

The company states that the device is simple to use and requires minimal training. Key aspects of the training involve understanding and using the available data. Training is tailored to the users and can be one-to-one or group training, and can be provided face-to-face or online via Microsoft Teams. Training for key users for each commission is included in the purchase price. Training videos and materials are available.


Technology costs

The NPi-200 consists of 2 components, the NeurOptics NPi-200 automated pupillometer and the NeurOptics NPi-200 'SmartGuard'. The SmartGuard reader is necessary to integrate the data into the electronic medical record. The barcode scanner avoids the need for manual input of patient data.

  • NeurOptics NPi-200 automated pupillometer: £4,155

  • NeurOptics NPi-200 SmartGuard: £396 for 24

  • Barcode scanner and charging cradle by socket: £475 to £595

  • SmartGuard reader: £150 to £195.

The company states that the NeurOptics NPi-200 automated pupillometer has an initial cost of about £4,000, which over a 5-year period with a cohort of 800 patients per year amounts to £1.00 per patient. The NeurOptics NPi-200 SmartGuard costs £16.50 per device. Each SmartGuard has an inbuilt radio-frequency identification chip that stores up to 168 paired measurements, which is enough for hourly pupil examinations over a typical 7-day stay in critical care (336 data sets per £16.50 or £0.049 per data set). The total cost of the NeurOptics NPi-200 and SmartGuard per patient for a 7-day stay in a critical care unit is therefore £17.50, or £2.50 per day.

Costs of standard care

Pupillary reactions are usually taken manually using a pen torch. One expert said that a pen torch costs approximately £1.50 and that most staff purchase their own.

Resource consequences

The company states that the technology is currently used in 28 NHS trusts.

The company claims that the use of the automated pupillometry can save valuable nursing time.

The raw data obtained from the automated pupillometer can be included in patient notes and changes tracked over time like other vital signs.