top of page

Pupillary Light Reflex

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 (ANS)


The ANS regulates bodily processes like heart rate, digestion, respiratory rate, and pupillary response without conscious control.


Pupillary Analysis

Over the last 70 years, medical and scientific studies have established that an individual PLR response is an excellent, non-invasive index of central nervous system functionality.

As a result, PLR alteration analysis is a proven and accepted method to reveal neurological anomalies. 


Interpreting the Test results

The test results are for information only


Test results are specific for each individual. The system automatically learns about their normal PLR response and a reference PLR baseline is established for each user.


During a test, the measured PLR response is compared against the individual’s baseline.  Differences in PLR response are reported as "PLR alteration detected".


A "No PLR alteration found" result indicates the absence of PLR differences compared to baseline.

SOBEREYE does not diagnose the underlying causes of changes in PLR and is not intended to be used by a physician to diagnose a medical condition.


PLR Research summary

(Bibliographic references)

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 [1] [2] [3], Jasinski [4] and Cone [5] have demonstrated a strong effect on pupil diameter and amplitude (both reduced) by all the major opiates including heroin, morphine, and codeine. 

  • Rowbotham [6] [7] has reported significant increases in pupil diameter for subjects given intravenous and oral cocaine. 

  • Tennant [8] has reported similar increases for amphetamines. Tennant also describes pupillary changes resulting from marijuana, benzodiazipines (Valium), alcohol and phencyclidine (PCP). 

  • Lowenstein [9] and Yoss [10] 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 [11].


[1]     H. L. a. P. J. F. Wallace B. Pickworth, Buprenorphine- Induced Pupillary Effects In Human Volunteers, vol. 47, Life Sciences, 1990, pp. 1269-1277.

[2]     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.

[3]     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.

[4]     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.

[6]     R. J. A. N. B. M.C. Robotham, "Trazadone-Oral Cocaine Interactions," Archives Of General Psychiatry, vol. 41, pp. 895-899, 1984.


[7]   W. H. J. M. a. R. J. M.C. Rowbotham, "Cocaine- Calcium Channel Antagonist Interactions," Psychopharmacology, no. 93, pp. 152-154, 1987.

[8]   F. Tennant, "The Rapid Eye Test To Detect Drug Abuse," Post Graduate Medicine, vol. 84, pp. 108-114, 1988.

[9]   O. L. a. I. Lowenfeld, "Types Of Central Autonomic Innervation And Fatigue," Archives Of Neurology And Psychiatry, vol. 66, pp. 581-599, 1951.

[10]   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.

[11]   P. S. a. J. T. R. Burde, Clinical Decisions In Neuro- Ophthalmology, The C.V. Mosby Company, 1985, pp. 221-245.

bottom of page