SI-traceability and digitalization of clinical intraocular-pressure measurement: a scoping review of the calibration chain, reference standards, measurement uncertainty, and machine-readable traceability

This is the authors' abstract. We don't add key points for this paper.

Intraocular pressure governs the diagnosis and management of glaucoma, yet whether the clinical result is metrologically traceable to the International System of Units (SI) has not been mapped, and neither has the digital infrastructure that would carry such traceability to the clinic. This review charted the published evidence on calibration, reference standards, measurement uncertainty, and digital traceability for clinical intraocular pressure, and located the points at which the chain from a primary realization of the pascal to the clinical reading is broken or unbuilt. Four bibliographic databases, conference and grey-literature sources, the International Organization for Standardization platform, and citation searching were examined, current to July 2026. Thirty-two sources were eligible. The defect located is not a missing calibration chain for the quantity the instrument realizes, which is a force over a defined area and is traceable, but an incompletely defined measurand: the quantity a tonometer realizes differs from the pressure of the aqueous humour by an eye-dependent, uncorrected amount, and no posture, time window, or reference plane is specified. The clinical reference compounds this, being instrument-defined: conformity is judged against a calibrated Goldmann-type tonometer rather than against the pascal. The most direct ground truth, intracameral manometry, is destructive and almost always performed ex vivo. National metrology institutes have built artificial-eye transfer standards and a calibration standard for non-contact tonometers whose realized pressure is traceable to the SI, but these remain single-laboratory developments that are not yet interlaboratory or clinically validated. Continuous sensors report indications on device-specific conventional scales rather than measured pressures. The wider metrology community is moving to machine-readable digital calibration certificates and shared measurement ontologies, yet no source reported an ophthalmic instrument participating in this digital chain, so no mechanism was identified by which tonometer calibration data could propagate automatically to the point of care. No published end-to-end in vivo chain with a stated expanded uncertainty was identified. Seven research priorities are proposed, of which the digitally native ones are the most tractable.