Definition and Overview
Pupillometry is a non-invasive test that evaluates the visual pathway and autonomic nervous system function by precisely measuring pupil responses to various optical or pharmacological stimuli.
Pupil size is controlled by the antagonistic actions of the parasympathetic nervous system (oculomotor nerve, CN III) and sympathetic nervous system (upper cervical sympathetic pathway). When the parasympathetic nerve is activated, the dilator pupillae muscle (sphincter pupillae) contracts and the pupil narrows, and when the sympathetic nerve is activated, the dilator pupillae muscle contracts and the pupil becomes larger. Pupillometry is a means of quantitatively evaluating the function of these two pathways.
Measurement principles and methods
Infrared Video Pupilometer
Using an infrared camera, the pupil boundary can be clearly captured even in a dark room or dark environment, enabling precise measurement in millimeter units. Because it is a non-contact method, patient discomfort is minimized.
stimulation protocol
- Light stimulus: After dark adaptation, a light stimulus of a certain intensity is applied to one or both eyes.
- Dark adaptation pupil measurement: resting pupil diameter
- Repetitive stimulation: continuous stimulation to measure pupillary fatigue index
Key Metrics
- Baseline pupil diameter at rest
- maximum constriction amplitude
- constriction latency
- Maximum constriction velocity: an indicator of parasympathetic function
- Relaxation velocity: an indicator of sympathetic function
- Fatigue index: rate of response decline upon repeated stimulation.
Clinical significance
Diabetic autonomic neuropathy
In diabetic patients, abnormalities such as reduced pupil constriction response, reduced pupil size at rest, and slow relaxation speed are observed. These changes can appear before the appearance of clinical autonomic symptoms and are therefore utilized for early detection.
Critical care monitoring
Automated infrared pupillometry is used to continuously monitor elevated intracranial pressure and brainstem function in intensive care units. Asymmetry or loss of pupillary response suggests midbrain compression or brainstem damage.
Locus coeruleus-norepinephrine system
The locus coeruleus in the brainstem simultaneously regulates arousal, attention, and pupil dilation. Since task-evoked pupil dilation increases proportionally to cognitive load, pain, and stress, it is used in research as a non-invasive indicator of locus coeruleus function.
POTS and autonomic disorders
Pupil abnormalities have been reported in patients with POTS (orthostatic tachycardia syndrome), complex regional pain syndrome (CRPS), and migraine. It is used as an auxiliary indicator that reflects the state of autonomic nervous system imbalance.
diagnosis
normal standard
Normal resting pupil size is approximately 3 to 8 mm (based on a dark environment) in adults, and decreases with age. The light reflex contraction width is generally at least 0.8 to 1.0 mm, and the contraction latency is generally within about 200 to 250 ms.
Inspection environmental conditions
For reproducible results, the test environment (lighting, temperature), use of drugs that affect the pupil (anticholinergics, myotics), and ophthalmic conditions (corneal disease, glaucoma) must be checked before the test.
In parallel with other tests
It is recommended that the pupillometry test be used in parallel with other autonomic nerve function tests, such as heart rate variability (HRV), cutaneous sympathetic response (SSR), and standing tilt table test, to evaluate autonomic function from various angles.
treatment
Since the pupillometry test is a diagnostic tool, there is no treatment for the test itself. Depending on the test results, appropriate treatment is provided for diseases that cause abnormalities in the autonomic nervous system (diabetes, Parkinson's disease, etc.).
Regular pupillometry tests can be used to track the progress of pupil-related autonomic nerve abnormalities, and are also used as an objective indicator of recovery of autonomic function after treatment.
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This information is provided for medical educational purposes and is not a substitute for individual medical care or treatment. If you have any symptoms, be sure to seek professional advice. Inquiries: Osang Neurosurgery 1599-5453 | osns.co.kr