Overview
ISO 19045:2015 - "Ophthalmic optics - Contact lens care products - Method for evaluating Acanthamoeba encystment by contact lens care products" defines a laboratory method to assess whether contact lens disinfecting solutions can induce encystment of Acanthamoeba trophozoites. The standard addresses procedure, controls and interpretation for encystment testing but does not evaluate disinfection efficacy. Oxidative systems that require a special lens case are excluded from this method.
Key topics and technical requirements
- Test organism: Acanthamoeba castellanii (ATCC 50370) is specified for the assay.
- Culture and media: Uses Ac#6 axenic semi‑defined growth medium and 1/4 strength Ringer’s solution; Sarkosyl–Calcofluor White reagent is used to lyse trophozoites and stain cyst walls.
- Sample handling: Three lots of product are tested; each lot uses a separate inoculum preparation to ensure reproducibility.
- Test format and volumes: Test and control solutions are dispensed into 12‑well plates (typically ~3.0 ml per well). A small aliquot of trophozoite suspension (e.g., 30 µl) is added to achieve a defined challenge concentration.
- Controls and replication: Plates include positive and negative encystment controls (positive control in triplicate; multiple negative control wells) and replicate test wells per product lot.
- Detection and timing: After exposure, detergent treatment and Calcofluor White staining are used; fluorescence microscopy (UV excitation/appropriate emission filter) distinguishes immature and mature cysts. A 5‑minute staining exposure is noted as critical for reliable counts.
- Equipment and conditions: Specifies microscopes (fluorescence and inverted), incubators (28 °C ±2 °C and 32.5 °C ±2.5 °C), centrifuge, vortex, and counting chambers.
- Validity criteria: The standard defines background cyst-level limits for the inoculum and prescribes procedures for counting and calculating encystment rates.
Applications and users
ISO 19045:2015 is practical for:
- Contact lens solution manufacturers performing product safety assessments for potential to induce Acanthamoeba encystment.
- Independent microbiology and contract testing laboratories validating product behavior against Acanthamoeba.
- Regulatory and quality assurance teams evaluating formulation safety risks linked to encystment and potential Acanthamoeba keratitis.
- Academic and clinical researchers studying amoebal encystment responses to ophthalmic care products.
This standard helps organizations identify formulations that may inadvertently promote Acanthamoeba encystment - a factor that can complicate subsequent disinfection - and supports risk assessment and product development decisions.
Related standards
- Related ISO guidance for ophthalmic optics and contact lens care products (standards addressing disinfection performance, labeling and safety) should be consulted alongside ISO 19045 when assessing overall product compliance, clinical risk and claims.
Keywords: ISO 19045, Acanthamoeba encystment, contact lens care products, contact lens disinfecting solutions, ophthalmic optics, encystment test, A. castellanii, Calcofluor White.