Eyes are the window to the soul. It’s possible to read a lot about people based on their eye behavior. But eyes are also the gateway to knowledge about how people gather information and what influences their actions and decisions. People have been interested in the concept of eye tracking since the 1800s – the first studies of eye movement were made using direct observations. Today we can bring all the power of tech to gather a lot of valuable insights about human behavior.

What is eye tracking

Eye tracking is a technology that measures eye movements and makes it possible to know where a person is looking, what they are looking at, and for how long their gaze is in a particular spot. The areas in which a user’s gaze stop moving are called “fixation,” while the movement of a user’s eye between fixation points is known as a “saccade.” By visualizing saccades, we can see the paths the eye is taking on a page.

It’s possible to understand both concepts by seeing how we read the text. We often hear that efficient readers ‘scan’ the text. In terms of eye movement, an efficient reader tends to have smaller fixations and longer saccades, while a weaker reader tends to have much longer fixations and much shorter saccades. The difference can be clearly seen in the image below. The one on the left is a stronger reader who moves quickly and easily through the text, while the one on the right is a weaker reader.

model showing eye tracking through fixation and movement
How does eye tracking work? Fixation time and eye movement. Image by Lexplore.

Below are three areas where eye tracking is especially useful.

Usability testing

How do users scan pages? What patterns do they follow? What are the elements that get most of their attention? These are typical questions during usability testing sessions. But when it comes to visual scanning behavior, it’s often hard (or nearly impossible) to ask test participants to recall their scanning patterns. Test participants may not remember their behavior (human memory is fallible), or they may be unable to verbalize the reasoning.

Eye tracking is the only method that can be used to objectively and accurately record and analyze visual behavior. Eye tracking allows you to uncover usability problems without disturbing natural user behavior. For example, it’s worth conducting eye tracking to understand whether your form field design is optimized for quick scanning – users can scan the form and understand all required fields at a glance.

Since eye tracking devices don’t depend on participant reports or memory, and all data is collected automatically, it makes eye trackers incredibly useful when researching a user’s visual behavior. By using this methodology, you can see live what the user sees and immediately understand where usability problems occur.


In modern ad services, the best metric advertisers get from ads are impressions and click through numbers. But those numbers do not precisely reflect the effectiveness of ad campaigns. Why? Because those numbers do not reflect whether a person actually viewed your ad.

Eye tracking technology can change that. Eye tracking helps to understand authentic user behavior, and this is very useful when designing advertising, branding, packaging, and product placement. With eye tracking technology, advertisers will be able to measure exactly how many human eyes actually view their ads when they appear on the page and their reactions were on the ad.

As input method

For decades, we’ve used keyboards, mice, and other peripherals to make computers understand where we’re looking at. But humans have one of the most powerful interaction methods – eyes.

Eye tracking can be used as an input method for human-computer interaction. It can be built into glasses or other wearable devices. Along with voice-based interactions, eye-tracking makes it possible to build more natural interactions with digital devices—natural user interfaces. In such interfaces, the eyes will be used as a “pointer” on a screen.

How does eye tracking work

An eye tracker consists of three elements—sensors, camera, and machine learning algorithms.

An eye tracker projects light onto the eye and sensors record the direction it’s reflected off the cornea. The camera takes multiple high-resolution images of the user’s eye. The position of the eye can be mapped multiple times a second.  After that, the machine learning algorithms process the image stream generated by the camera and determine exactly where the eye is focused.

step by step guide to how eye tracking works
Step-by-step process for how eye tracking works. Image by tobiipro.

Eye tracking visualizations and product design

Eye-tracking tools output some compelling visualizations that can benefit product design process. By analysing eye tracking visualization, product designers can understand how users perceive and understand the content and UI design elements. For example, if users don’t interact with a particular element (i.e., call-to-action button), eye-tracking can tell you if this element is even in the gaze path of users.

The most common visualizations are heatmaps and gaze point plots.


A heatmap is a view of where one participant (or every participant) in a study looked. A heatmap is created based on fixations— places where participants look for 100 to 500 ms.  Hot areas of the map show areas with more participant fixations.

heat map of a web page
A heatmap looks like a weather map, but instead of the temperature, hot areas are based on fixations. Image by baymard.

Gaze point plots

Most eye-tracking tools have the ability not only to show the areas where users look the most, but also to connect fixation points to provide the path a participant’s eye travels as they view the page or screen. Gaze point plots allow the researcher to see not only what items interest the participant but also the order in which the participant is looking at them.

gaze plot diagram
Gaze point plot diagram. Image by researchgate.

Eye tracking VR

When it comes to eye tracking, no other field benefits from it as much as virtual reality. Eye tracking is an essential technology for VR design. VR is about immersion, and eye tracking technology helps create this sense of immersion. VR headsets with integrated eye tracking allow situational interactions to be examined in various environments without the need for the environment to be physically present. VR can help train people in places that would otherwise be too risky to be in. For example, students studying to become doctors can use VR to practice medical procedures they may encounter when they get into the field.

But eye tracking is also solving a specific hardware problem—rendering 3D objects in VR space. To create a sense of immersion, we need to create realistic objects around the user. But since our current hardware resources aren’t perfect, we need to optimize the process of rendering. This is where eye tracking comes to save the day. Foveated rendering is a technique where only a portion of the image that lands on the fovea is rendered in full quality. With this technique, it’s possible to decrease the number of pixels drawn and achieve higher frame rates and better-quality output.

Improving VR with NVIDIA’s Foveated Rendering.

How to use eye tracking in usability testing

There is no better way to test user experience than to view it through the eyes of the user. But to make the most of eye tracking it’s vital to consider a few simple rules.

Review testing techniques you have in your toolbox

Eye tracking studies take time. You need to recruit test participants, prepare an environment for testing, and spend time analyzing results after the testing. That’s why when you define the scope for testing, don’t jump into eye tracking. Consider whether you can utilize less expensive testing methods to the best of their potential. For many projects, low-cost methods such as contextual inquiry, user interviews or even A/B testing can be enough information to help a team make informed decisions.

Understand the goal of testing and select relevant test participants

Similar to any other usability testing, it’s vital to establish what question (or questions) you want to have answered. Based on the goal, you will define a scope for your testing (tasks).

When it comes to eye tracking, it’s vital to understand that the task the user is trying to achieve matters greatly. If the tasks don’t resonate with test participants, they will follow a path of least resistance and eye tracking won’t bring much value.

Recruit enough test participants

The number of test participants should be selected based on the nature of testing. In the article Eye Tracking: What Is It For And When To Use It,  Neil Dawson provides the following practical recommendations:

  • For manual analysis of recordings. It’s enough to have five test participants for qualitative eye tracking tests where recordings are manually reviewed.
  • For automatic analysis of recordings. The automated analysis creates an aggregated view of several participants on a heatmap. If you want to have meaningful heatmaps and gaze plots that aggregate the actions of many users, it’s necessary to recruit at least 39 participants.

He also suggests having at least two facilitators present in each session— to ensure nothing is missed and allow each to take a break.

Select the testing environment

Do you want to set up an in-house eye tracking team or outsource it? It’s recommended to set up an in-house eye tracking team if:

  • You have people in your team with a research background (preferably, practical skills in eye tracking). Remember, you will need to collect the data and analyze it. Without the right skills, it’s easy to overlook important details.
  • You have the resources to purchase equipment and train staff to use it.
  • You know that eye tracking is the right technique for your project (meaning you plan to run it regularly).

Gaze replay retrospective

It’s recommended to conduct an interview with test participants after the session and replay eye gaze patterns on top of the task recording. When participants see their own behavior, it will help them remember some of their actions, and you will get more detailed feedback about user behavior. It’s worth also to ask test participants about the emotional state during the session.

Don’t use it as a replacement for other testing tools

Don’t think of eye tracking as a silver bullet for your testing. It’s not a replacement for other usability testing techniques. Remember that eye tracking is a more quantitative type of testing rather than qualitative. The data from an eye tracking study will help you understand that users spend more time fixating on a certain element, but it won’t tell you why. The qualitative information can only be discovered through interviewing.


Eye tracking is the emerging tech that has a potential to change the way we build products. Being able to see the user’s natural interaction with products and services enables researchers to identify real usability problems. Used together with other research and testing techniques, eye tracking can be a source of valuable information that will provide insights into user satisfaction and engagement and will help drive design decisions.