What requirements does IEC 62366 place on usability?

Usability is part of product safety

IEC 62366-1:2015+A1:2020 primarily considers safe operation of a medical device rather than comfort or aesthetic design. The standard describes a usability engineering process that identifies and reduces risks from correct use and from use errors. Deliberate actions that fall outside any reasonable use are excluded from this consideration.

The regulatory reference is found in the MDR: Annex I Number 5 requires risks to be minimized as far as possible through ergonomic features and the use environment, taking into account the knowledge, experience, training, and physical capabilities of the intended users. For products intended for use by laypersons, Annex I Number 22 contains additional requirements.

What must be documented

A robust process includes at least:

• a Use Specification with medical purpose, user profiles, patient groups, use environment, and functional principle,
• the description of safety-related characteristics of the user interface,
• known or foreseeable use errors and hazard-related usage scenarios,
• a user interface specification with verifiable requirements,
• an evaluation plan as well as results of formative and summative testing,
• the linkage of results with the risk file according to ISO 14971,
• a traceable usability engineering file.

Formative evaluations accompany the development. Prototypes, comprehension tests, or observations with representative users are used to identify weaknesses early and improve the design. Summative evaluations assess the safety-critical usage scenarios on a sufficiently representative, final, or production-like interface. This is not about a general satisfaction rating, but about objective data on successful, erroneous, and near-error actions and their causes.

Software requires a realistic context

In medical software, not only individual screen masks are part of the interface. Alarms, error messages, data imports, units, default values, timing behavior, and transitions between devices or roles can also be safety-relevant. A clinical professional at the workplace, a patient at home, and an administrator have different knowledge and risks. Therefore, tests should realistically depict the intended roles, tasks, devices, lighting and noise conditions, and time pressure.

The number of test subjects is not replaced by a single universal number from the standard. It must be justified based on user groups, risk, scenarios, and evaluation goals. IEC 62366-1 provides the process; whether a specific design is safe enough remains a product-specific, documented decision.