On Usability
Introduction
When hearing the term “usability,” one might imagine “ease of use.” However, usability in the context of medical devices is not merely about “ease of use.” Rather, it represents a human factors engineering approach designed to achieve safety and effectiveness.
The Essence of Usability Engineering
The FDA historically used the term “Human Factors Engineering (HFE)” and did not formally employ the term “usability engineering” for many years. The reason for this distinction lies in the fundamental objective of medical devices: they are not designed primarily to be easy to use, but rather to ensure safety.
In reality, devices are sometimes intentionally designed to be difficult to use for safety reasons. For example, a lighter is designed with a heavy ignition button that makes ignition difficult. This design is not a usability failure; rather, it is a safety design that reduces the risk of children accidentally starting a fire. Thus, “difficulty of use” when implemented for safety purposes is an important concept included in medical device usability engineering.
The Relationship Between Risk Management and Usability Engineering
The author is frequently asked about the distinction between “Risk Management” and “Usability Engineering.” In fact, usability engineering is encompassed within risk management, though with a different scope of application.
Risk Management (ISO 14971) covers normal use, abnormal use, and misuse. In contrast, Usability Engineering (IEC 62366-1) focuses on use errors that occur during normal use. Abnormal use and intentional misuse are not included within the scope of usability engineering.
In other words, usability engineering is a process that focuses on “Use Errors” occurring in normal usage environments and aims to prevent and reduce their occurrence.
Accurate Understanding of “Use Error”
It is necessary to have an accurate understanding of the term “use error.” Use error is not synonymous with human error. While human error refers to inattention or misjudgment by the user, use error is a broader concept.
For instance, depending on user characteristics (age, physical capability, education level, language proficiency, medical knowledge, etc.), a user may be unable to use a device correctly even with the intention to do so due to insufficient strength, reduced vision, inability to read text, or inability to understand medical concepts. In such cases, the “error” does not result from user limitations but rather stems from problems in medical device interface design.
Furthermore, use errors often result from poor interface design of medical devices. When an interface has confusing displays, ambiguous operating methods, difficult-to-identify indicators, or easy-to-confuse control layouts, use errors can occur even when the user has the correct intention. The responsibility for preventing such errors lies with the device designer.
The Multifaceted Nature of Interfaces
In usability engineering, attention is focused on such interface design when implementing risk management. The scope of interfaces is not limited to electronic display devices such as liquid crystal displays (LCDs). It encompasses everything recognized through human senses, including vision, hearing, and touch.
Interface elements that should be considered in medical device usability engineering include instructions for use and user guidance materials, labels and displays, control elements such as buttons and dials, the shape of the medical device, color design, and alarm sounds and other alert functions. These are all elements that form the interaction between users and medical devices and influence the risk of use errors.
Understanding Gaps Between Device Accidents and Design
Medical device accidents and adverse events frequently result from gaps between “actual user behavior” and “the design intent of the medical device designer.” This phenomenon has been repeatedly demonstrated through FDA and EU MDR regulatory literature and analysis of incident reports.
If device designers fail to adequately understand how users actually use medical devices, what misconceptions or misidentifications are likely to occur, and what physical and cognitive limitations users face, there is a risk that interface design will deviate from actual user behavior.
Whether interfaces are designed to be intuitive, understandable, and resistant to errors depends on how well medical device designers understand the usage environment, user characteristics, typical usage behaviors, and foreseeable misuse possibilities. For this reason, the usability engineering process includes use research involving actual users and healthcare professionals, use simulations, and usability evaluation testing.
Implementation of the Usability Engineering Process
IEC 62366-1 and IEC 62366-2 define a systematic usability engineering process with the following stages.
The usability engineering process for medical devices begins during the design and development phase. First, user characteristics, usage environments, and foreseeable use scenarios are analyzed in detail to identify “use-related hazards.” Next, usability requirements are defined based on these hazards. Subsequently, interface design and design measures to prevent use-related adverse events are implemented. After design completion, usability evaluation testing with actual users is conducted to verify whether use errors occur, their frequency, and their severity. Based on these evaluation results, design improvements are implemented as necessary.
Finally, a Usability Validation File is created to maintain records of all usability engineering activities. This is an important document submitted during medical device regulatory submission (FDA 510(k), EU MDR technical documentation).
Latest Regulatory Trends
In the latest guidance from FDA and EU medical device regulations, the importance of usability engineering is increasingly emphasized. Particular attention has grown in the following areas.
With the increase in medical devices corresponding to Digital Health and Telemedicine, there is a need to address usage environments that go beyond traditional face-to-face use frameworks. Additionally, for medical devices incorporating Artificial Intelligence (AI) and Machine Learning, interface design that supports users in interpreting results and making judgments has become an important theme in usability engineering.
Furthermore, the balance between cybersecurity and usability has been recognized as a new challenge. While security requirements necessitate password complexity and multi-factor authentication, it is necessary to ensure that these measures do not compromise the usability of healthcare professionals’ daily workflows.
Conclusion
The safety and effectiveness of medical devices ultimately depend on how correctly and safely end users can use them. Usability engineering is an essential process for achieving this goal and is not merely an ancillary design activity but rather a core component of medical device development.
Those involved in medical device development must understand the essence of usability engineering and incorporate this process from the initial stages of design and development.
For further information, please refer to usability engineering-related international standards (IEC 62366-1, IEC 62366-2), official FDA/EU guidance documents, and video recordings of seminars on usability engineering presented by the author.
