Overview
ISO 18369-3:2017, "Ophthalmic optics - Contact lenses - Part 3: Measurement methods", defines standardized methods for measuring the physical and optical properties of finished contact lenses. It covers procedures for radius of curvature, label back vertex power, diameter and zone widths, thickness, edge inspection, detection of inclusions/surface imperfections, and spectral transmittance. The standard also specifies the equilibrating and standard saline solution used when testing lenses.
Key topics and technical requirements
- Measurement scope: Methods apply to parameters referenced in ISO 18369‑2 and are intended for finished contact lenses.
- Radius of curvature: Includes optical spherometry (microspherometer), ophthalmometry (ophthalmometer with lens attachment) and sagittal‑height methods for hydrogel lenses.
- Representative reproducibility values reported in the standard: optical spherometry ±0.015 mm (air); ophthalmometry ±0.015 mm (air) and ±0.025 mm (saline). Sagittal methods show larger reproducibility depending on water content (e.g., ±0.05 mm to ±0.20 mm).
- Label back vertex power: Procedures for focimeter specification, calibration and measurement of rigid and soft (hydrogel) lenses, including methods for measuring soft lenses immersed in saline.
- Dimensional measurements: Total diameter, zone diameters/widths and thickness methods (dial gauge, low‑force mechanical gauges).
- Optical and visual inspection: Defined procedures for edge inspection, identifying inclusions and surface imperfections.
- Spectral transmittance: Instrument specifications, test conditions and procedures for measuring lens transmittance across relevant wavelengths.
- Equilibration and saline solution: Definition, formulation, preparation, packaging and labelling of the standard saline solution to be used for equilibrating lenses before measurement.
- Quality/performance expectations: Methods should achieve precision where repeatability and reproducibility meet specified limits (each method capable of R&R ≤ 30% of allowed tolerance range). Lenses must be equilibrated until measured parameters stabilize.
- Reporting: The standard includes requirements for test reporting of measurement results and method conditions.
Applications and who uses it
ISO 18369-3:2017 is used by:
- Contact lens manufacturers and suppliers for quality control and product release testing
- Accredited testing laboratories performing compliance or conformance testing
- Regulatory bodies and notified bodies reviewing measurement data for market approval
- Equipment manufacturers (focimeters, microspherometers, ophthalmometers) to align device specifications with standard methods
- Research and development teams validating designs and materials
Practical benefits include consistent, traceable measurements across suppliers and labs, improved product comparability and clearer acceptance criteria for manufacturing and regulatory compliance.
Related standards
- ISO 18369‑1:2017 - Vocabulary, classification and labelling for contact lenses
- ISO 18369‑2 - (Referenced) specifications for contact lens properties
- ISO 3696 - Water for analytical laboratory use (relevant for saline formulation)
- ISO 9342‑1 - Test lenses for focimeter calibration
Keywords: ISO 18369-3:2017, contact lenses, measurement methods, radius of curvature, label back vertex power, spectral transmittance, standard saline solution, contact lens testing, focimeter, ophthalmometry.
