Pupillary Light Reflex (PLR)
The Pupillary Light Reflex (PLR) is an involuntary reflex that controls the size of the eye’s pupil in response to changing light intensity. Pupil constriction and dilation are controlled by the Autonomic Nervous System that regulates bodily functions like heart rate, digestion, respiratory rate, and pupillary response without conscious control.
Over the last 50 years, many medical and scientific studies have established that an individual PLR response is an excellent, non-invasive index of central nervous system function.
As a result, PLR alteration analysis is a proven and accepted method to evaluate brain function and it is widely used to measure neurological anomalies, the metabolism of drugs, and in fitness-for-duty applications to detect drug impairment and sleep deprivation.
Pupillary analysis is used by doctors in hospitals and intensive care units and involves the use of a pupillometer, an instrument that provides a measurement of pupillary size, symmetry, and reactivity.
Medical grade pupillometers are used in a wide range of areas including anesthesiology, drug addiction, endocrinology, psychiatry, refractive surgery and sleep disorders.
Pupillary analysis is used by police, it is performed in a subjective manner by using a penlight or flashlight to manually evaluate pupil reactivity and using a pupil gauge to estimate pupil size, as is done by trained police officers. However, this kind of manual pupillary assessment is subject to significant inaccuracies and inconsistencies.
Pupillometry in fitness-for-duty screening
Fit-for-duty means that an individual is in a physical and mental state to be able to perform the essential tasks of his or her work assignment in a manner which does not threaten the safety or health of oneself, co-workers, property, or the public at large. The PLR is sensitive to a variety of impairing drugs, sleep deprivation and other impairing neurological conditions, as such, pupillometry can be used for impairment risk detection and fitness-for-duty applications.
SOBEREYE INC. has pioneered the use of smartphones in automated pupillometry.
The patented technology uses latest generation smartphones, together with an opaque enclosure, to make accurate PLR measurements. The visor is used to hold the phone and positions it correctly over the users eyes. Each measurement is compared against an individual’s baseline (normal) PLR.
The innovative approach to pupillary analysis uses off-the-shelf HW (smartphone), machine learning and the cloud to provide a convenient and effective solution to improve workplace safety by measuring impairment risk on-the-job, in real time, when it matters most.
PLR Research summary
The correlation between PLR alterations and impairing neurological conditions has been extensively studied, here is summary of some of the findings and bibliographic references.
Pickworth   , Jasinski  and Cone  have demonstrated a strong effect on pupil diameter and amplitude (both reduced) by all the major opiates including heroin, morphine, and codeine.
Rowbotham   has reported significant increases in pupil diameter for subjects given intravenous and oral cocaine.
Tennant  has reported similar increases for amphetamines. Tennant also describes pupillary changes resulting from marijuana, benzodiazipines (Valium), alcohol and phencyclidine (PCP).
Lowenstein  and Yoss  studied changes in the shape and stability of the pupil light reflex as a person moves from alertness through fatigue to sleep. The findings show that extreme fatigue causes reduced pupil diameter and unstable pupil responses.
Pupillary changes also occur in some neurological conditions. Profound pupillary changes are often observed as a result of brain lesions or tumors as well as impending stroke .
 H. L. a. P. J. F. Wallace B. Pickworth, Buprenorphine- Induced Pupillary Effects In Human Volunteers, vol. 47, Life Sciences, 1990, pp. 1269-1277.
 P. W. J. H. a. E. C. Wallace B. Pickworth, Opiate-Induced Pupillary Effects In Humans, vol. Methods And Findings In Experimental Pharmacology, 1989, pp. 759-763.
 R. V. F. a. E. B. B. Wallace B. Pickworth, "Effects of abused drugs on pupillary size and light reflex," in Drug Abuse Handbook, CRC Press LLC, 1998.
 P. J. F. A. R. E. J. Donald R. Jasinski, "Sublingual Versus Subcutaneous Buprenorphine in Opiate Abusers," Clinical Pharmachology & Therapeutics, 1989.
5] E. J. Cone, "Testing Human Hair For Drugs Of Abuse. Individual Dose And Time Profiles Of Morphine and Codeine In Plasma, Saliva Urine and Beard Compared to Induced Effects On Pupils And Behavior," Journal Of Analytical Toxicology, no. Jan-Feb, 1990.
 R. J. A. N. B. M.C. Robotham, "Trazadone-Oral Cocaine Interactions," Archives Of General Psychiatry, vol. 41, pp. 895-899, 1984.
 W. H. J. M. a. R. J. M.C. Rowbotham, "Cocaine- Calcium Channel Antagonist Interactions," Psychopharmacology, no. 93, pp. 152-154, 1987.
 F. Tennant, "The Rapid Eye Test To Detect Drug Abuse," Post Graduate Medicine, vol. 84, pp. 108-114, 1988.
 O. L. a. I. Lowenfeld, "Types Of Central Autonomic Innervation And Fatigue," Archives Of Neurology And Psychiatry, vol. 66, pp. 581-599, 1951.
 N. M. a. R. H. R. Yoss, "Pupil Size And Spontaneous Pupillary Waves Associated With Alertness, Drowsiness and Sleep," Neurology,, vol. 20, pp. 545-554, 1970.
 P. S. a. J. T. R. Burde, Clinical Decisions In Neuro- Ophthalmology, The C.V. Mosby Company, 1985, pp. 221-245.