Pupil Analysis

OSDx can be used either for a simple pupil diameter measurement or for a full dynamic pupillary light reflex study. Dynamic measurements add information about afferent visual pathways and parasympathetic and sympathetic autonomic function.

How to do the test

Ask the patient to look straight ahead. Focus the pupil and iris pattern of the eye being measured clearly in the live image.
OSDx uses infrared illumination for imaging. Infrared light itself produces little or no visible-light stimulus, so the resting pupil diameter is determined mainly by the ambient visible-light conditions.
For a scotopic pupil measurement: make the room as dark as practicable and allow the pupil to adapt before capturing the diameter. A measurement taken in ordinary room illumination should not be interpreted as a true scotopic pupil diameter.
For a full pupil study: explain the sequence before starting. Ask the patient to avoid blinking once the study begins. Warn the patient that a bright flash will occur approximately 5 seconds after the start and that recording will continue for a further 5 seconds.
Keep fixation steady throughout the study. Reposition or repeat the test if the pupil margin is poorly focused, substantially obscured by the lids or lashes, or if a blink interrupts the critical light-response period.

Tip: Ambient illumination, recent near fixation, medications, age, emotional arousal and adaptation time can all influence pupil size. For serial comparison, perform measurements under similar room conditions whenever possible.

Two pupil analysis modes

Simple pupil diameter

Records the resting pupil diameter without a dynamic light-response sequence.

Clinical relevance: useful when pupil size itself is the principal measurement—for example pre-operative planning, refractive and optical assessment, anisocoria documentation, and comparison of pupil size under controlled photopic or scotopic conditions.

For a clinically meaningful scotopic value, the room should be made as dark as possible and sufficient dark adaptation allowed.

Full pupil study

Records the pupil before, during and after a standardized light stimulus, allowing the dynamic pupillary light reflex to be quantified.

Clinical relevance: changes in response amplitude, latency, constriction and redilatation can provide objective evidence of altered retinal/optic-nerve input or altered parasympathetic and sympathetic autonomic function.^1–4

Dynamic pupillometry is an adjunct to—not a replacement for—the conventional pupil examination, RAPD testing and a complete neuro-ophthalmic or neurologic assessment.

Understanding the full-study parameters

Scotopic / baseline pupil diameter

The resting diameter immediately before the visible-light stimulus. It reflects the balance between parasympathetic pupillary constriction and sympathetic dilator tone, and is strongly affected by ambient illumination, dark adaptation and age.

Can be smaller with: increasing age, miotic drugs, Horner syndrome, parasympathetic dominance and some autonomic neuropathies.

Can be larger with: anticholinergic or sympathomimetic drugs, third-nerve parasympathetic dysfunction, Adie-type tonic pupil during the earlier phase, reduced ambient illumination and physiologic sympathetic activation.

Photopic / minimum pupil diameter

The smallest pupil diameter reached after the flash. It depends on baseline pupil size and the strength and integrity of the light reflex. A relatively large minimum diameter may reflect reduced constriction, but should always be interpreted together with baseline size and the dynamic response.

Latency

The interval between the light stimulus and the onset of measurable constriction. It includes retinal phototransduction, afferent transmission through the optic nerve and pretectal pathways, central processing and the early efferent parasympathetic response.

Prolonged or asymmetric latency may occur with: optic nerve or retinal dysfunction, afferent pathway disease, severe glaucoma, diabetic neuroretinal/autonomic dysfunction and other neurologic disorders affecting the pupillary pathway.^1–4

Constriction time / constriction response

Describes the dynamic parasympathetic phase after the flash. Depending on the displayed OSDx metric, a prolonged constriction phase or sluggish response indicates that the pupil reaches its minimum diameter more slowly.

Constriction may be reduced or slowed in:

Parasympathetic dysfunction affecting the Edinger–Westphal pathway, oculomotor nerve, ciliary ganglion or short ciliary nerves.
Adie tonic pupil, classically with a slow tonic constriction and especially slow redilatation.
Diabetic autonomic neuropathy, in which abnormalities of pupil size and light-reflex dynamics can precede or accompany other signs of autonomic dysfunction.^2,3
Retinal and optic-nerve disease, because weaker afferent drive may reduce the amplitude and alter the kinetics of the light reflex; quantitative abnormalities have been described in glaucoma and diabetic retinal disease.^1–4
Pharmacologic inhibition by anticholinergic/mydriatic agents. Opioids and other centrally acting drugs can also alter pupil size and reflex dynamics.

A very small baseline pupil can mechanically limit the measurable amount of further constriction, so absolute values should not be interpreted without considering starting diameter.

Redilatation time / redilatation response

The recovery phase after maximum constriction. Early redilatation is produced largely by withdrawal of parasympathetic activity, with sympathetic dilator activity contributing increasingly to later recovery. Consequently, redilatation can be altered by disorders affecting either autonomic limb.^4,5

Redilatation may be delayed or abnormal in:

Adie tonic pupil—slow redilatation is a characteristic clinical feature.
Autonomic neuropathy, including diabetes, where both sympathetic and parasympathetic abnormalities may affect pupil dynamics.^2,3
Horner syndrome / sympathetic pathway dysfunction, particularly when dilation in darkness is assessed; the affected pupil classically shows dilation lag.
Drug effects, including anticholinergic, adrenergic, opioid and sedative agents.
Neurologic and neurodegenerative disorders in which central autonomic regulation is altered. Dynamic pupillometry has been investigated in several such conditions, but individual metrics are not disease-specific.^4,5

Clinical patterns that can alter pupil dynamics

Condition / influence	Possible pupillometry finding	Clinical point
Optic neuropathy / asymmetric afferent disease	Reduced or delayed response when the affected afferent pathway is stimulated	Interpret with RAPD testing and the complete optic-nerve examination.
Glaucoma	Reduced constriction amplitude and altered pupil dynamics have been reported, particularly with greater neural damage.^1,4	Pupillometry is supportive; it is not a stand-alone diagnostic test for glaucoma.
Diabetes / diabetic autonomic neuropathy	Smaller resting pupils and altered latency, constriction or redilatation may occur.^2,3	Changes may reflect autonomic as well as retinal/neural involvement.
Adie tonic pupil	Sluggish tonic constriction and characteristically slow redilatation	Correlate with anisocoria, near response and pharmacologic testing where appropriate.
Horner syndrome	Miosis with impaired/delayed dilation in darkness	Dilation lag is a sympathetic sign; routine flash-response metrics alone are not diagnostic.
Third-nerve parasympathetic dysfunction	Larger pupil with weak or absent constriction	An acute pupil-involving third-nerve palsy requires urgent clinical evaluation.
Retinal disease	Reduced or altered afferent light response depending on the retinal pathway involved^4,6	Chromatic pupillometry can separate photoreceptor pathways more specifically; the standard OSDx flash study should be interpreted more generally.
Medications / substances	Baseline size and constriction/redilatation may all change	Record topical and systemic drugs before interpreting unexpected findings.
Age and ambient light	Older age generally produces smaller pupils; brighter ambient light reduces baseline diameter	Standardize test conditions for follow-up comparisons.

Interpretation points

Compare both eyes

Inter-eye asymmetry can be more informative than an isolated value, especially when testing for asymmetric afferent or autonomic dysfunction.

Control the environment

Baseline diameter is highly illumination-dependent. Serial tests should use similar lighting, fixation and adaptation conditions.

Check medications

Topical mydriatics/miotics and many systemic drugs can substantially alter pupil measurements.

Use clinically

No single dynamic parameter is specific for one disease. Interpret the OSDx result together with symptoms, ocular examination and neurologic findings.

Important: Quantitative pupillometry supports clinical assessment but does not by itself establish a neurologic, autonomic, retinal or optic-nerve diagnosis.

References

Park HYL, et al. Dynamic pupillometry and autonomic dysfunction in glaucoma. Scientific Reports. 2019.
Karki SB, et al. Dynamic pupillometry in type 2 diabetes and diabetic retinal neuropathy. 2020.
Halperin A, et al. Pupillary light reflexes and autonomic neuropathy in diabetes. 2016.
Philibert M, et al. Basics, benefits and pitfalls of pupillometers assessing the visual system. 2024.
Hall CA, Chilcott RP. The pupillary light reflex as a tool for assessment of autonomic and neurologic function. 2018.
Rukmini AV, et al. Chromatic pupillometry methods for assessing photoreceptor and retinal ganglion-cell function. 2019.