1 Legibility is not a property of the label alone

Font size, typeface, contrast and layout shape the label legibility on medical devices and packaging. From a human factors perspective, however, legibility only arises from the interplay of several factors:

• label and packaging design,
• printing and material properties,
• lighting conditions,
• viewing angle and distance,
• visual acuity and vision aids of the users,
• available time and parallel tasks,
• prior knowledge and expectations regarding the information being sought.

Label legibility is therefore a sub-area of packaging usability. A basic classification of packaging as part of the user interface can be found in the article Usability evaluation of medical device packaging. This article addresses one section of it: the question of how the recognizability of information can be investigated realistically.

Labeling is part of the user interface: the FDA Human Factors Guidance explicitly names packaging, labeling and training materials as examples in its definition of the user interface, and in usability engineering according to IEC 62366-1, accompanying information is also considered together with the product. The IMDRF principles of labeling likewise require that the medium, format, content, legibility and position of the labeling suit the device, its purpose and its users.

In addition, ISO 20417 specifies which information the manufacturer must provide, and ISO 15223-1 specifies which symbols are used on the labeling of medical devices. Both standards describe what belongs on a label and how symbols are to be used. Whether the information is actually found and understood in the context of use is only shown by the usability evaluation.

A label can be clearly recognizable under controlled conditions and still be overlooked or misinterpreted in the context of use. Particularly susceptible are glossy surfaces, low contrast, small print, visually similar product variants and information that only becomes visible when the packaging is turned.

2 Why lighting conditions make the difference

Light does not only affect whether characters are visible. It also changes information search, color recognition and the differentiation of similar design elements. Relevant influencing factors include, for example:

• reduced ambient lighting,
• directional light and cast shadows,
• glare and reflections on films or coated surfaces,
• different color temperatures,
• changes between bright and dark areas, for example between a display and the surroundings.

Which conditions belong in a test follows from the context of use and the disturbing factors of the use environment. Packaging for a brightly lit preparation room places different demands than a product used in a darkened examination room, in an emergency response or in the home environment.

2.1 User group and vision conditions

Light does not affect all users equally. How well information is recognized under reduced lighting or glare also depends on visual acuity. Vision aids, protective glasses or visors can change the field of view and contrast perception. For products intended for home use, lay users with very different visual acuity are added.

These differences belong in the description of the intended users and in the user profile. They determine which participants are needed for a readability test and which aids are permitted in the test. A test that is conducted only with participants with very good visual acuity and without protective equipment underestimates the difficulties in everyday use.

3 Four levels of legibility

To make clear where a difficulty arises, four levels should be observed separately in the test.

3.1 Visual perceptibility

Can users perceive characters, symbols, colors and boundaries? Influencing variables are font size, stroke width, contrast, surface reflection, print quality, distance, angle and illuminance. The wiki entry Perception describes the fundamentals.

3.2 Findability

Do users find the information they need? Information hierarchy, grouping, position and visual anchors count here. An item can be easily legible and still not be found because it is located in an unexpected place.

3.3 Distinguishability

Can similar product variants or items of information be reliably told apart? This is particularly important when the packaging of a product family is structured identically and differs only in color, abbreviation or small parts of the text.

3.4 Comprehensibility

Do users understand the information they have found as it is intended? Purely text-based methods, which evaluate word and sentence lengths, for example, give indications of linguistic complexity. However, they do not show whether users implement information correctly in a specific situation.

4 What can be investigated formatively

A formative usability evaluation is intended to identify weaknesses early and improve design solutions. Typical questions for labels are:

• Which information do users look at first?
• Is safety-relevant information found in time?
• Which items of information are overlooked under reduced lighting?
• Do reflections or glare occur that prevent reading?
• Are similar variants confused?
• Does the search strategy change under different light?
• Which information is found but misinterpreted?

Compensation strategies are particularly revealing. When participants turn a package several times, bring it closer to their face, hold it up to the light, use a lamp or ask others for help, this shows potential for optimization, even if the task is solved in the end.

In our readability tests we see this behavior again and again: participants turn the packaging, bring it closer to their eyes or hold it up to the light before they find the information they are looking for. This is exactly where the root cause analysis begins.

4.1 When to test in the development process?

A readability test is worthwhile as soon as the layout and information hierarchy of a label are fixed, but print data and packaging material can still be changed. Early on, printouts on the intended material or simple samples are often sufficient. Later, near-series samples with the original surface should be tested, because gloss, film and printing process strongly influence reflection. A second, shorter round after design changes shows whether the measures work and no new problems have arisen. A test is also useful when a product family is extended by new variants, because the risk of confusion then increases.

5 A possible study design

5.1 Analyze the context of use

Before selecting the lighting conditions, clarify: Who uses the product, where and at what time? Which information must be recognized then? Which use errors or delays could occur? Not every conceivable lighting situation has to be simulated. The selection should be derived from the context of use and the use-related risk analysis, for example from the hazard-related use scenarios.

5.2 Define information tasks

Instead of asking whether a label is legible, formulate concrete tasks, for example:

• Identify the required product variant.
• Find the size specification.
• Locate the warning notice.
• Distinguish between two similarly designed variants.
• Determine the next action step.

Task-based tests show whether the labeling supports actual use.

5.3 Vary lighting conditions in a controlled way

Depending on the context of use, several defined conditions can be investigated, for example reference lighting, reduced lighting, directional light, unfavorable incident light with reflection and the change between a bright and a dark environment. The conditions should be documented and reproducible. In addition, viewing angle, distance and available time can be varied.

We conduct such readability tests in our Medical Usability Test Lab. The lighting there can be adjusted from complete darkness to operating room lighting. This allows us to recreate both darkened examination and patient rooms and brightly lit procedural situations, and to keep the conditions the same for each session.

DIN EN 12464-1 can serve as a guide for realistic lighting levels. The standard describes requirements for the lighting of indoor workplaces, including areas in healthcare. Decisive for the test, however, remains the specific context of use of the product.

5.4 Capture behavior instead of opinion

Statements such as “I could read that well” are helpful, but should not be the only data source. More meaningful are observable data: time to find the information, area looked at first, repeated searching, turning or tilting of the packaging, shortened distance, confusions, omitted information and the success rate per information task. The think-aloud method can additionally show what participants are looking for.

5.5 Debrief on causes

Ask specifically after each task: What was difficult to recognize? Where was the information expected? What helped, what distracted? Was the difficulty visual, linguistic or structural? The goal is not a list of preferences, but a traceable link between context of use, observed behavior and design cause, that is, a root cause analysis.

5.6 Select participants

A formative readability test does not require large samples, but it does require the right participants. They should represent the intended user groups, including typical vision aids and, where relevant, the protective equipment worn in the context of use. Also include participants with different lengths of professional experience. Experience can influence how information is searched for, for example whether someone relies on familiar positions and colors or reads the label completely. More on selection can be found in the wiki entry Representative users.

5.7 Document test conditions

So that results are traceable and later iterations are comparable, the conditions should be recorded for each session: illuminance at the label, type and position of the light sources, color temperature, viewing distance and angle, and the prototype or print status used. Photos of the setup from the participants’ point of view help with later root cause analysis. This documentation is also the bridge to the summative evaluation: it shows which conditions have already been investigated and which still have to be covered there.

6 What a formative readability test can and cannot do

A formative test can make weaknesses visible early, compare design variants, identify problematic lighting and viewing situations, support the use-related risk analysis and make requirements for the later summative evaluation more concrete.

However, it is not conclusive proof. Especially with small samples or non-final prototypes, no general statements about the usability of the final product can be derived. The communication of results should reflect this clearly: the formative evaluation identifies possible weaknesses and supports design decisions. It does not prove that a label is safely legible under all lighting conditions.

For the regulatory classification, the distinction is important: IEC 62366-1 distinguishes formative evaluations, which iteratively improve the design, from the summative evaluation, which demonstrates safe use on the final design. Questions about the legibility of safety-relevant labeling that remain open formatively should therefore flow into the planning of the summative evaluation as concrete tasks or knowledge questions.

For product and development teams, early testing is worthwhile mainly for one reason: confusion of similar variants or late label changes shortly before the summative evaluation or market launch cost time, because print data, packaging and documentation have to be adapted again.

7 From observation to design decision

The value of a formative evaluation only arises through its translation into measures. Possible measures are higher contrast, adjusted font size or stroke width, less glossy surfaces, a different prioritization and grouping of content, critical information on several visible surfaces, stronger differentiation of similar variants, color coding with additional features and clearer symbols.

Do not correct every observation in isolation. Changes create new interactions. A larger font can improve legibility and at the same time change information density and hierarchy. An iterative sequence has proven effective: observe, analyze the cause, adapt the design, investigate again.

A simple matrix helps to translate observations into measures in a structured way:

Each row is a hypothesis that is verified in the next round.

Conclusion

Labels are not static carriers of information, but part of the user interface. Whether labeling works depends not only on font size, contrast and mandatory information, but on whether relevant information is found, distinguished and understood under realistic conditions.

Formative readability tests under varying lighting conditions make exactly this interaction visible early. They create a robust basis for design decisions and for planning the summative evaluation.

In the Medical Usability Test Lab of USE-Ing., we investigate labeling and packaging under defined lighting conditions and translate observations into concrete design requirements. If you would like to test a label realistically before release, get in touch with us.

Frequently asked questions about label legibility

Further content

• Usability evaluation of medical device packaging
• Formative usability evaluation according to IEC 62366-1
• Hazard-related use scenarios and use-related risk analysis
• Wiki: Labeling, Packaging usability, UDI, ISO 20417

Sources

• IMDRF/GRRP WG/N52 FINAL:2024 (Edition 2): Principles of Labeling for Medical Devices and IVD Medical Devices, April 26, 2024, Section 5.1.1: imdrf.org (PDF)
• IEC 62366-1:2015+AMD1:2020 / DIN EN 62366-1, Medical devices, Part 1: Application of usability engineering to medical devices: https://www.dinmedia.de/de/norm/din-en-62366-1/338440028
• FDA: Applying Human Factors and Usability Engineering to Medical Devices: https://www.fda.gov/regulatory-information/search-fda-guidance-documents/applying-human-factors-and-usability-engineering-medical-devices
• ISO 20417:2021, Medical devices, Information to be supplied by the manufacturer: https://www.iso.org/standard/67943.html
• ISO 15223-1:2021, Medical devices, Symbols to be used with information to be supplied by the manufacturer, Part 1: General requirements: https://www.iso.org/standard/77326.html
• DIN EN 12464-1:2021, Light and lighting, Lighting of work places, Part 1: Indoor work places: https://www.dinmedia.de/de/norm/din-en-12464-1/334047306

1 Why packaging is more than product protection

The primary function of medical device packaging is, of course, to protect the product, to maintain sterility up to the point of use and to avoid damage during storage and distribution. For sterile products, however, a second, equally critical function applies: the packaging must support users in presenting the product quickly, correctly and aseptically. Its quality is therefore measured not only by how well it protects a product, but also by how safely it prepares its use.

It is exactly at this interface between packaging development, user interaction and clinical context of use that safety-relevant problems often arise in practice.

In the operating room, the cath lab, the emergency department or in outpatient care, packaging is rarely opened under ideal conditions. Users work under time pressure, with gloves, limited fine motor skills, sometimes restricted vision and high cognitive load. Under these conditions, seemingly small design features can have a considerable effect on how safely a product is presented.

Examples include:

• opening starting points that are hard to recognize
• high or inconsistent peel forces
• unclear removal directions
• unfavorable product orientations
• labeling that is hard to read

If relevant information is not found quickly or opening the packaging is made unnecessarily difficult, users often develop their own strategies to complete the task anyway. From a human factors perspective, this is not primarily an individual failure, but an indication of deficits in the usability of the system.

In this understanding, packaging usability becomes a distinct level of consideration. It describes the ability of a packaging system to support users in the safe, efficient and intended presentation of a product. For sterile medical devices in particular, it is therefore an essential building block for safe aseptic presentation and for avoiding use-related risks.

It becomes clear: packaging is not just a logistical or material component. It is part of an overall system of product, labeling, instructions for use, training and context of use. From a human factors perspective, packaging elements therefore also belong to the components that can influence the safe and effective use of a medical device.

2 What risks arise from poor packaging usability?

Weaknesses in packaging usability can lead to relevant risks along the entire path of use. Particularly critical are contamination events during aseptic presentation, damage to the product when opening, wrong removals, mix-ups of similar variants and delays in clinical workflows. Many of these problems are not only packaging problems, they develop into use-related risks in the context of use. They rarely occur as isolated events, but are an expression of systemic design weaknesses.

Scientific studies show that the design of the packaging system can significantly influence the likelihood of contamination. Studies on the aseptic presentation of different sterile barrier systems indicate that certain packaging concepts support users better than others in presenting sterile products safely. Even seemingly small design features can have a relevant influence on the risk of contamination.

Studies show, for example, that factors such as the curling of the packaging material or the structure of a peel pouch can influence whether sterile contents come into contact with non-sterile surfaces. Packaging systems that support outward rolling of the material led to lower contact rates than alternative designs in the scenarios examined.

In addition, many of these problems are not recognized or reported as packaging problems in the field. Clinical users often attribute difficulties with opening or aseptic presentation to individual clumsiness, time pressure or routine deviations. As a result, part of the actual usability problems remains underreported in complaint data, CAPA processes or post-market surveillance activities.

From the perspective of human factors engineering, this is particularly relevant. If users repeatedly develop workarounds or use packaging differently than intended, this should not be interpreted solely as user behavior. Often it is a signal that the packaging design does not sufficiently take the requirements of the real context of use into account.

3 The regulatory framework: what is expected today

An important turning point was the revision of ISO 11607-1:2019. While earlier discussions about packaging were often dominated by material properties, seal integrity and validation of the barrier function, the current version explicitly contains new requirements for the usability evaluation of aseptic presentation. This acknowledges from a regulatory perspective that safe sterile presentation depends not only on material and process validation, but also on the real interaction of the user with the packaging. Human factors and usability standards, including IEC 62366-1 and AAMI HE75, focus on the interfaces of devices: controls, displays, software and workflows. The interaction with primary and secondary packaging belongs to this as well.

ISO 11607 requires not only proof of a functioning package. The standard also indirectly requires proof of a functioning interaction with that package.

Specifically, ISO 11607-1 requires a documented evaluation of whether sterile contents can be removed or presented aseptically from the sterile barrier system.

This evaluation should cover at least three aspects:

1. the ability to identify the starting point for opening,
2. the ability to recognize the required opening technique and to carry it out correctly without contaminating or damaging the contents or the packaging, and
3. the ability to subsequently present the contents aseptically.

The topic is also relevant from the point of view of European regulation. The EU MDR emphasizes the need for safe handling and the avoidance of microbial contamination. Secondary literature and specialist publications therefore increasingly make clear that packaging should no longer be regarded as a side issue separate from the product, but as a safety-relevant part of the overall system.

4 Why packaging usability is still often considered too late in projects

Despite clearer regulatory requirements, packaging usability remains underrepresented in many development projects. The cause is usually not a lack of competence, but a lack of integration. Packaging engineers typically focus on material selection, seal strength, sterile barrier, manufacturability, cost and distribution testing. Human factors teams, on the other hand, often focus on the medical device itself, its controls, displays, software, labeling or instructions for use. Packaging thus sits between several disciplines and not infrequently falls through the organizational cracks.

As a result, key decisions on packaging concepts are often made before representative users have even interacted with early design variants. At that point, functions, materials or packaging architectures are often already largely fixed. Insights from later user evaluation then no longer lead to small optimizations, but to potentially far-reaching changes.

Typical consequences are:

• adaptations of packaging concepts in late project phases
• additional verification and validation activities
• revalidation of packaging processes
• changes to labeling or IFU
• additional regulatory effort

The later use-related problems are recognized, the higher effort, costs and project risks generally become.

A robust usability evaluation of medical device packaging should not be understood as an isolated one-time test at the end of a development project. It is rather a continuous process that considers packaging design, context of use and user interaction along the entire development cycle.

This is a particular feature of medical device packaging: many risks arise not from material failure or loss of the sterile barrier, but only during the interaction between user and packaging. If these interactions are only examined shortly before verification or validation, essential design decisions have often already been made.

5 What a standards-compliant usability evaluation of packaging can look like

The starting point is therefore the analysis of the context of use. This is not only about the packaging itself but about the situation in which it is used. User groups, critical tasks, work environments and potential influencing factors have to be considered.

Examples include:

• sterile handovers in the operating room
• working with double gloves
• one-handed operation
• time pressure in emergency situations
• restricted visibility
• high cognitive load

Only when these conditions are understood can it be assessed which requirements a package actually has to meet.

Formative evaluation: recognize design weaknesses early

In the next step, early packaging concepts should be examined formatively. The aim is not the formal proof of usability, but the early identification of weaknesses in the design.

Typical questions are:

• Is the opening starting point recognized intuitively?
• Is the opening direction clear?
• Does the product stay correctly oriented after opening?
• Can the packaging be opened safely with gloved hands?
• Is there a risk for aseptic presentation?
• Is relevant information grasped quickly?

Especially in early development phases, small studies with representative users can provide valuable insights and avoid costly changes in later project phases.

Summative evaluation: proof under realistic conditions

For the summative or validating evaluation, a use scenario that is as realistic as possible is decisive. The aim is to evaluate the packaging under conditions that come as close as possible to the later context of use.

Simulated clinical environments are often used for this. Published studies used, for example, simulated operating room scenarios and UV-based methods to make contacts between sterile and non-sterile surfaces visible. Such approaches enable a more objective evaluation of aseptic presentation and help to identify the causes of observed use difficulties systematically.

This is exactly why the summative evaluation should not only examine the opening of the packaging, but consider the complete task that users actually have to perform.

From packaging test to system evaluation

One of the most important insights of modern human factors approaches is that packaging problems rarely arise from individual material properties alone. What matters is the interaction between packaging, product and context of use.

A standards-compliant usability evaluation therefore delivers far more than regulatory evidence. It creates the basis for recognizing potential use-related risks early and for designing packaging systems so that they actively support the safe and efficient use of a medical device.

6 Which usability aspects are particularly relevant for packaging

Not every challenge in packaging projects is recognizable at first glance. In practice, however, the same questions keep appearing that have a direct influence on the safe and efficient use of a medical device. Many of these aspects look like details of the packaging design at first. In fact, they can be decisive for whether a product can be presented correctly and aseptically under real conditions of use.

The following aspects are particularly relevant:

Findability of the opening starting point

Is it recognizable at first glance where and how the packaging has to be opened? Unclear opening points often lead to searching behavior, additional hand movements or improvised opening strategies.

Required opening force and handling

Can the packaging be opened safely with gloved hands without provoking jerky movements or the use of additional tools? Peel forces that are too high or inconsistent can impair both control of the product and aseptic presentation.

Contamination risk through material behavior

Does the packaging material behave predictably during opening? Unfavorable curling, uncontrolled tearing or problematic peel paths can cause sterile contents to come into contact with non-sterile surfaces.

Orientation and presentation of the contents

Is the product presented after opening in a way that supports safe, fast and correct removal? An unfavorable orientation can require additional manipulation and increase the risk of error.

Comprehensibility of labels and labeling

Can important information be grasped quickly and reliably? This includes, among other things:

• product identity
• product size or variant
• sterility status
• expiry date
• relevant distinguishing features

Especially under time pressure, this information must be immediately available.

Robustness against real contexts of use

Does the packaging concept also work under the conditions in which it will actually be used? Relevant influencing factors are, for example:

• time pressure
• distractions
• restricted vision
• working with gloves
• high workload
• unplanned interruptions

These aspects are not cosmetic optimizations. In many cases they act as direct or indirect risk control measures. Their design influences whether users can perform critical tasks safely, efficiently and as intended.

7 Recommendations for manufacturers

For manufacturers of sterile medical devices, this has a clear consequence: packaging development should not be viewed exclusively as a packaging topic. The safe presentation of a product arises at the interface of packaging design, user interaction and context of use. Accordingly, packaging usability should be understood as an interdisciplinary task from the start.

Packaging engineering, human factors engineering, risk management, clinical/medical, quality and regulatory affairs should therefore define joint requirements early and view packaging as part of the entire user interface system. Only in this way can technical, regulatory and use-related requirements be brought together systematically.

In practice, the following measures in particular have proven effective:

• include packaging in the use-related risk analysis in early concept phases
• carry out formative evaluations with representative users
• systematically simulate critical use situations
• link requirements from ISO 11607 and IEC 62366 early
• treat packaging usability as a distinct part of verification and validation strategies
• analyze packaging-related complaints and use signals systematically in the post-market phase

Equally important is the continuous observation of real use experience after market launch. Difficulties with opening, improvisations during aseptic presentation or recurring workarounds often provide valuable indications of optimization potential, even if no formal complaints or safety-relevant events are reported.

Anyone who addresses packaging usability only shortly before design freeze or approval risks unnecessary iterations, increased validation effort and avoidable regulatory discussions. If packaging is instead considered early as part of the use system, risks can be controlled more robustly and design decisions can be made on a sounder basis.

Conclusion

The question today is no longer whether the usability of packaging is relevant, but how systematically it is integrated into development processes. Packaging does not only protect the product. It influences whether a medical device can be presented at the point of use safely, efficiently and free of contamination.

This is exactly where the growing importance of packaging usability lies. The interaction between user and packaging helps decide whether a product can be used as intended. Packaging is therefore not only a packaging system, but at the same time part of the use system and a potential source of use-related risks.

The systematic evaluation of packaging usability requires close integration of packaging engineering, human factors engineering, risk management and regulatory know-how. Manufacturers that view packaging early as part of the user interface system create not only a more robust basis for compliance and risk management, but often also develop more robust and more user-friendly products.

Support along the development process

USE-Ing. accompanies manufacturers of medical devices from the early concept phase to summative validation. We support the identification of packaging-related use-related risks, the planning and execution of formative and summative usability evaluations and the standards-compliant documentation according to ISO 11607 and IEC 62366-1.

By using realistic use scenarios and established human factors methods, we help to identify critical weaknesses early and to develop robust packaging solutions.

Please get in touch if you want to integrate packaging usability systematically into your development process. You can find more information on the process of a systematic usability engineering of packaging here:

Frequently asked questions about packaging usability

Further reading

• Human Factors & Usability Engineering for Medical Devices
• Testing Label Legibility Under Realistic Lighting Conditions
• ISO 11607-1:2019, Packaging for terminally sterilized medical devices – Part 1: Requirements for materials, sterile barrier systems and packaging systems
• IEC 62366-1:2015+A1:2020, Medical devices – Part 1: Application of usability engineering to medical devices
• AAMI HE75:2025, Human Factors Engineering – Design of Medical Devices