Usability Engineering plays a critical role in medical device design with the ultimate goal of mitigating the risk of human errors that impact the system state, the operator and patient. The pervasive trend of utilizing embedded interfaces in medical devices has called a great deal of attention to the criticality of usability testing. This attention has also been fueled by an FDA spokesperson revealing that “more than one half of the recalls due to design problems can be traced to the design of the user interface.” Usability testing is not a commodity; it is a necessity. 

The key to usability testing is identifying any potential risks and errors that could result in injury to the patient or administrator. This risk identification can and should also extend to other individuals that interact with the device, starting with sterilization all the way to transportation. The necessity of usability testing is also echoed in a number of standards including ISO/IEC 62366: Medical Devices – Application of Usability Engineering to Medical Devices, HE75 and Code of Federal Regulations on Quality System Regulation 820.30.

Sections (f) and (g) of 820.30 both speak to user testing such that the “design verification shall confirm that the design output meets the design input requirements” and “design validation shall ensure that devices conform to defined user needs and intended uses and shall include testing of production units under actual or simulated use conditions.” Although these standards have long been considered with respect to the physical aspects of medical devices, it is important to note that it doesn’t stop at the interface. These same standards, and a plethora of others, need to be considered with regard to the graphical user interface.

Guidelines – How do we start?

Prior to testing, one of the ways to frame the usability of a medical device is by identifying the various human factors and ergonomics guidelines that help direct the product design ranging from button size and arrangement to luminance of visual displays to weight limits for hand held components. This activity also serves as a way to identify guidelines and principles that need to be met during the iteration of the designs complementing findings from usability testing. Additionally, what are the primary use cases? What are existing mental models that are driving the information architecture? Has the architecture been validated by subject matter experts?

Testing and Validation

The key to effective usability testing is to carry out iterative testing starting with early formative testing to later summative testing. Formative testing allows the opportunity to identify potential usability issues early on and iterate the early design accordingly. Also known as directional testing, this formative type of testing provides information regarding impressions of products at various stages in the process Ideally, multiple rounds of formative testing allows developers to refine the product design further mitigating any potential risk and user error. Validation testing provides a “last” check that ensures the design integrity and purpose has been met by the design and that the product is “usable” based on the various metrics, such as user performance.

Regulation & HF

All of the aforementioned testing meets, at a high level, the various activities described in the standards provided above. However, it is equally important that any type of testing has been designed in a manner that is appropriate for:

  • Potential users of the product
  • Environment of use
  • Various levels of interactions
  • Various use cases (setup to breakdown)

Global Considerations

Oftentimes, usability testing can be shortsighted with testing only in the United States for instance. There are a host of implications with any product or interface that is to be launched globally. Usability testing is key to identifying any cultural nuances that may affect or be affected by a design. The use of any icons in a product can also pose a number of translation issues as those most accepted in the U.S. may have very different meanings in other countries. Localization of text can also serve to be barriers in GUI design resulting in various design accommodations. The global aspect of the GUI should not be ignored.

Taking into account the ecosystem of a product will result in better usability testing and is core to the latest standard, HE75 which encourages the use of simulated environments and high fidelity prototypes with the ultimate goal of greater confidence in usability findings.