Creal: A radically new way of subjective refraction

What does the future of subjective refraction look like? A Swiss start-up has an answer: refraction should be digital, offer almost unlimited display options, and also be independently manageable by the customer. Subjective refraction with the help of light field displays would therefore change the traditional way of doing the subjective refraction with a phoropter or trial frame set tremendously. Even a “refraction automate” in a shopping center is theoretically conceivable in the future. This article explains how the technology works and what it offers. We also spoke to Dr. Tomas Sluka, developer and founder of the ­­­start-up CREAL, in an interview.

Subjective refraction has not changed significantly for 100 years. Opticians, optometrists and ophthalmologists normally use a phoropter or trial frame set to practice their conscientiously learned craft. But is this type of refraction really still up to date?

The new technology from the company CREAL, founded in 2017, offers completely new possibilities for subjective refraction. A prototype with the light field display technology is currently being tested by various players in research and industry.

The system is not yet on the market, but that is only a matter of time. Zeiss Vision Care has recently invested in CREAL and both companies signed a license agreement.

The idea

The Swiss startup was founded with the mission to develop a near-eye 3D display taking care of the user’s eyes. The developed light field display technology should enable users to have a healthy and natural visual experience of digital imagery, by supporting the natural behavior of the human eye. This new type of display system provides correct focal depth to the digital content, and can place it at any optical distance and/or respectively apply arbitrary spherical, astigmatic or prismatic power to the projected image.

Furthermore, images with different corrections at different distances can be applied and displayed simultaneously. Any device built on such technology could be also made “intelligent” and controlled by a simple touch screen, allowing for an unassisted procedure carried out by the eye care practitioner and, if appropriate, the patient.

Therefore, the company believes that digital near-eye light field display could bring a revolution to numerous optometric, optical and ophthalmological applications, especially in subjective refraction.

The digital light field display

Light field imagery is a genuine representation of how light exists in the real world. It therefore provides highly realistic digital imagery with natural focal depth, enabling the digital content to blend seamlessly with the real world, and removing any visual conflict causing eye strain and nausea.

The light field display technology projects a sequence of slightly different perspectives of a digital scene (the light field) to the eye. Each perspective/image is projected through its corresponding virtual viewpoint placed by the user’s pupil. By sending more than 6000 in-focus images per second, the full 3D digital scene is recreated in front of the user’s eyes.

The digital light field technology is also suitable for displaying graphically rich content in VR and AR. CREAL already embeds it in its patented light field headset evaluation kits (Fig. 1.4).

Digital light field technology for optometry

Current eye examination procedures have not changed much in over 100 years; with eye care practitioners (ECPs) still using physical lenses and test charts in refraction. Optometry products based on the new digital light field technology can bring a significant change to the industry and can offer many advantages.

Self-contained, space efficient and simultaneous displaying of different powers

The device based on the digital light field technology is fully self-contained. The displayed image originates directly in the device itself with optical distance reconstructed fully digitally.

The size of the device is to be further reduced in the future, resulting in a small, effective tabletop instrument or even a head-mounted VR headset.

Furthermore, different spherical and astigmatic power can be displayed simultaneously. Objects or images with different optical power applied can be shown next to each other in a single screen. This brings several benefits:

• The user can easily compare which image is seen best, because the user sees them simultaneously next to each other. For example, letters with a range of diopters are shown simultaneously.
• Simultaneous or comparative images projected at the same time (especially for astigmatic evaluation) give the user more confidence in their answer. ECPs might hear less often: “I am not sure”.
• The user can identify which is seen best, picks it and quickly moves to a finer refraction selection.
  The comparison between different powers next to each other allows for faster assessment than comparing one after another in traditional devices.
• The process can remove the need for initial measurement with an autorefractor.

Real-world images and instant change of digital content

The user is shown real-world images and any flat image, 3D object, or even animations can be displayed. This means:

• More relevant and recognizable scenarios can be displayed to evaluate refraction.
• A variety of different symbols or images, including 3D objects, can be used for children or adult patients for whom standard symbols might be hard to recognize/name.
• Application-specific symbols can be designed.
• Information can be displayed to guide the user through the procedure.

It is also possible to show users relevant imagery such as computer screens, mobile phones, and television. And images are seen at appropriate distances, all at the same time.

Additionally the shown content can be changed digitally. The device enables randomized permutation of Snellen chart letters’ position and prescription for each measurement. This prevents users from learning the chart leading to more reliable testing procedures. Each patient and each measurement will be unique.

And the test procedure is very simple: with a click by the patient or ECP, new and specific images can be instantly changed, taking the eye test along a defined and automated route to determine the refraction. The change of content is instant (<1/30 s), similar to a change of picture on the screen of a mobile phone. The same applies to the change of spherical or astigmatic power.

Flexible spherical power and astigmatic power

As the optical power is generated digitally, it is not tied to a set of pre-existing lenses. Therefore, its range and fineness are not limited by a set of physical lenses. A major benefit is that any prescription (or comparative prescriptions) can be generated rapidly and not limited by physical lens combinations.

• Spherical power steps can be adjusted in increments: <0.1 D.
• Spherical power range is large (-15.00D to +12.00D)
• The same range applies to astigmatic power (-5.00D to +5.00D)
• Prismatic powers can be applied.
• Presbyopic prescriptions can be evaluated easily with near-field imagery.

Interactive and fully user-controlled and/or automated procedures

Since the device is based on digital light field technology, it can be controlled through a tablet or similar interface. This allows CREAL to design an interface that fully guides the user through the entire procedure.

• Automated procedures: no need for lengthy subjective assessments during the normal procedure.
• Multiple devices supervision by one staff member.
• Multiple procedures can be combined.
• Procedures can be entertaining (e.g. for children or patients with special needs).
• Measurement procedures can be updated over the internet, allowing immediate deployment of new procedures through the retail network without costly and time-intensive staff retraining.
• Specific tailor-made procedures can be designed for niche customers and markets.
• Other device input (autorefractor, lensometer) can be incorporated.

New classes of devices and use cases

All of the above and future advancements can allow for the development of completely new test procedures or even treatment procedures; for example: Interactive games to stimulate development focusing abilities, such as treating amblyopia/lazy eye.

But also, color vision screenings, binocular vision testing, visual fields examination, pilot or driver training procedures and much more. Future potential is not limited to simple refraction.

This article is a summary of the CREAL´s vision care white paper. For further questions please contact: visioncare@creal.com

On the next page follows an interview with developer and founder of the start-up CREAL Dr. Tomas Sluka.