ISO 18369-4:2017

Overview

ISO 18369-4:2017 - Ophthalmic optics - Contact lenses - Part 4: Physicochemical properties of contact lens materials - defines standardized test methods for measuring the key physicochemical characteristics of contact lens materials. The standard covers extractables, rigid lens flexure and breakage, oxygen permeability (Dk), refractive index, and water content, and specifies apparatus, reagents, procedures and reporting requirements used by testing laboratories, manufacturers and suppliers.

Key topics and technical requirements

• Scope and applicability

  • Applies to hydrogel and non‑hydrogel contact lens materials and is intended for testing laboratories, suppliers and users who require measurement data to demonstrate compliance.
  • Alternative methods are permitted if accuracy and precision are equivalent or better than those specified.

• Extractables

  • Uses standard Soxhlet extraction with water and appropriate organic solvents to quantify substances extractable from lenses.
  • Dry mass difference before and after extraction determines extractables; extracted material can be analyzed by chromatographic or spectrophotometric techniques.

• Rigid lens flexural deformation and rupture

  • Procedures for sampling, sample preparation, apparatus and test procedures to measure flexural deformation and rupture loads for rigid lenses.

• Oxygen permeability (Dk)

  • Oxygen permeability is reported in Dk units (barrer). The standard includes the polarographic method, normalization of corrected oxygen permeability using reference lenses, and an informative annex on the coulometric method.
  • Repeatability target and measurement conventions are described.

• Refractive index

  • Methods include measurement using an Abbe refractometer; an informative annex describes prism coupling techniques.
  • Specified expression of results and reporting formats.

• Water content

  • Primary method is gravimetric determination by loss on drying (oven). An informative annex covers determination by refractive index.
  • Repeatability and reporting instructions provided.

• Repeatability and precision

  • The document requires laboratories to establish repeatability and reproducibility (R&R). It gives guidance on acceptable precision in method development (R&R ≤ 30% of allowed tolerance) and provides example repeatability values (e.g., Dk 10%, refractive index 0.01, water content 2% absolute).

Practical applications and who uses this standard

• Contact lens manufacturers and material suppliers - for material characterization during development and quality control.
• Testing laboratories and QC facilities - to perform standardized measurements for compliance, product release and comparative studies.
• Regulatory affairs and conformity assessment - to substantiate product safety and performance claims with standardized test data.
• R&D teams and clinicians - when evaluating new materials or comparing material properties relevant to ocular physiology (oxygen transmission, hydration, optical properties).

Related standards

• ISO 18369-1:2017 - Vocabulary, classification system and labelling recommendations for contact lenses.
• ISO 18369-3:2017 - Measurement methods (related measurement procedures).
• ISO 3696 - Water for analytical laboratory use (referred for reagent quality).

Keywords: ISO 18369-4:2017, contact lens materials, physicochemical properties, oxygen permeability, Dk, extractables, refractive index, water content, Soxhlet extraction, polarographic method.