Overview
EN ISO 22665:2012 (ISO 22665:2012) specifies requirements and test methods for instruments that measure the axial length of the human eye. Applicable to both ultrasound biometry and optical biometry (e.g., partial coherence interferometry), the standard defines minimum performance criteria, verification procedures and documentation/marking expectations for axial length measuring devices used in ophthalmic optics and clinical practice. A primary goal is to reduce systematic measurement differences between biometers that can affect intraocular lens (IOL) power calculations for cataract and refractive surgery.
Key Topics and Requirements
- Scope and definitions: Defines axial length (from anterior corneal surface to ILM or RPE) and modes such as phakic/aphakic, contact/immersion ultrasound and optical biometry.
- Performance tolerance: Measurements on specified test bodies must lie within ±100 µm of true dimensions.
- Test methods:
- Use of cylindrical test bodies positioned to mimic clinical eye alignment.
- For each orientation, 10 independent measurements are performed and averaged.
- Temperature corrections required for sound velocity (ultrasound) and group refractive index (optical) of the test material.
- Test bodies:
- Normative Annex A describes cylinders (l = d) typically made from PMMA with tight manufacturing tolerance (≤ 0.01 mm). Cylinder sets represent short, medium and long eyes.
- Material properties (group refractive index, sound velocity, acoustical impedance) must be specified and used in conversions.
- Instrument modes: Procedures for contact and immersion ultrasound and for optical devices obtaining optical path length are specified.
- Accompanying documents and marking:
- Must include manufacturer details, disinfection instructions, user instructions and a reference to ISO 22665 if claiming compliance.
- Permanent marking must show manufacturer, model and serial number.
- Normative reference: IEC 60601-1 (medical electrical equipment safety) is cited.
Applications and Who Uses It
- Medical device manufacturers of axial length biometers (ultrasound and optical) use EN ISO 22665 for product design verification and CE/national compliance.
- Clinical engineers and calibration laboratories apply the test methods to verify device accuracy and to calibrate instruments.
- Ophthalmic surgeons and clinics rely on compliant devices to improve IOL power calculation accuracy for cataract and refractive surgery.
- Regulators and notified bodies reference the standard during conformity assessment and performance evaluation of ophthalmic equipment.
Related Standards (if applicable)
Keywords: ophthalmic optics, axial length measuring device, optical biometry, ultrasound biometry, ISO 22665, axial distance measurement, PMMA test cylinders, IOL calculation, medical device standard.
