Overview
ISO 18369-2:2017 - Ophthalmic optics: Contact lenses - Part 2: Tolerances defines the manufacturing tolerance limits for the principal optical, dimensional and material properties of rigid corneal, rigid scleral and soft contact lenses. The standard applies to lenses “at the time of manufacture” and supplements measurement and material test methods referenced in ISO 18369-3 and ISO 18369-4. Note: these tolerances may not apply for other purposes (for example, shelf-life studies).
Key topics and requirements
- Scope and test conditioning
- Specifies that lenses shall be equilibrated in standard saline or packaging solution prior to testing (unless otherwise indicated in the referenced test methods).
- Conformance methods
- Recognizes three conformance approaches: 100% inspection, acceptance sampling and statistical estimation of performance (supplier data or third‑party audits can be used).
- Dimensional tolerances
- Rigid lenses: back optic zone radius, optic zone diameter, total diameter, centre thickness, bifocal segment height, fenestration/truncation limits (e.g., back optic zone radius tolerances can be as tight as ±0.025 mm for some rigid lenses; total diameter tolerances typically ±0.10 to ±0.25 mm).
- Soft lenses: back optic zone radius/equivalent posterior radius ±0.20 mm; sagitta ±0.05 mm; total diameter ±0.20 mm; centre thickness tolerance based on nominal thickness (formulas provided).
- Optical tolerances
- Label back‑vertex power tolerances vary with power magnitude (e.g., rigid lenses ±0.12 D to ±0.50 D depending on dioptric range; soft lenses ±0.25 D to ±1.00 D depending on power).
- Cylinder power and axis tolerances (axis ±5°; cylinder power bands have defined tolerances).
- Material and physical properties
- Spectral transmittance in the visible: ±5% absolute.
- Ultraviolet transmittance classification: Class 1 and Class 2 limits are defined for UVB/UVA when UV absorption is claimed.
- Oxygen permeability (Dk): ±20%; water content ±2% absolute; refractive index tolerances for rigid lenses.
- Finish and defects
- Lenses must be free of inclusions/surface imperfections that interfere with function; fenestrations and edge finish examined at ≥7× magnification.
- Manufacturer deviations
- Deviations from the standard tolerances are permitted where supported by clinical data (ISO 11980) and risk assessment (ISO 14971).
Applications - who uses this standard
- Contact lens manufacturers (design validation, production tolerancing, quality control)
- Test laboratories and third‑party auditors (conformance testing to ISO 18369-3 / -4 methods)
- Regulatory and compliance teams (device filing and labeling claims, UV or aspherical design claims)
- Suppliers and contract manufacturers (specification control and acceptance criteria)
- Eye care researchers and clinicians (understanding manufacturing variability and clinical implications)
Related standards
Keywords: ISO 18369-2, contact lens tolerances, ophthalmic optics standard, contact lens manufacturing, Dk oxygen permeability, UV transmittance, soft contact lens tolerances, rigid contact lens tolerances.
