The Pupillary Light Reflex (PLR) is an involuntary eye reaction that adjusts the pupil size according to light intensity. For over a century, this reflex has been a reliable indicator of autonomic nervous system activity — and thus, of a person’s responsiveness.
Early clinical studies
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In the 19th century, European doctors began using handheld flashlights to observe how pupils reacted in patients with neurological conditions.
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These observations were subjective and depended on the doctor’s experience, but already showed that PLR changes were linked to brain injuries, substance use, and altered states of consciousness.
Development of automated pupillometry
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In the 1950s, the first electronic pupilometers emerged, enabling more precise recording of pupil size and movement.
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These devices marked a major shift, transforming pupillometry into an objective, quantifiable measurement used in neurology, anesthesiology, and intensive care.
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Pioneering studies (Lowenstein & Loewenfeld, 1958) confirmed that PLR is a sensitive indicator of autonomic nervous system state and the presence of fatigue or drugs.
Applications in research and medicine
In the following decades, pupillometry expanded across various fields:
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Critical care: assessment of patients in coma or under anesthesia.
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Neuroscience: study of cognition and emotional responses.
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Forensic medicine and traffic: detection of drug and alcohol use.
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Psychology: analysis of attention and cognitive processing.
From clinics to industry
With advances in digital technology, pupillometry reached new environments:
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High-resolution smartphone cameras helped replace bulky, expensive equipment.
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The combination of dark visors and image analysis algorithms enabled portable, fast, and standardized PLR testing.
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This opened the door for use beyond hospitals — in HSE departments as a preventive tool to assess worker fitness before critical tasks.
Conclusion
The history of pupillometry shows a clear evolution: from manual and subjective clinical technique to digital, objective, and portable testing. Today, thanks to PLR analysis, HSE departments have a tool that bridges decades of medical research with modern risk management.