Incorporating User Prescription Optics in AR/MR Devices

Roughly 64% of the U.S. population wears prescription lenses of some kind¹, and an estimated 2.2 billion people globally require vision correction.² Vision typically worsens with age (84% of adults over 45 use vision correction³), driving increased demand for prescription eyewear due to aging of large population cohorts in many developed nations. The need for corrective lenses is also increasing in younger populations: roughly 40% of children under age 18⁴ are developing myopia and now require vision correction, a figure that has doubled since the 1970s. If the trend continues, half of the world’s population will be short-sighted by 2050⁵. 

Rising education levels, although beneficial to society, mean more time spent in classrooms and a corresponding decrease in the amount of time spent outdoors, reducing the amount of time children focus their eyes in the medium and far-distance. Other factors such as increased screen time due to lifestyle trends and changes due to the COVID-19 pandemic are also known to cause visual fatigue in young people⁶. As a result of these population trends, the demand for prescription optics in NEDs will likely increase as the AR/VR/MR (collectively XR), HMD, and smartglasses market segments mature. 

Incorporating Prescription Optics Into AR/MR Headsets & Smartglasses

To make AR/MR devices practical for this large swath of potential users, makers of smartglasses face a two-fold challenge. First, they need to incorporate display technology with customizable optics that match each wearer’s unique prescription. Approaches include devices manufactured with permanent custom-made prescription lenses, after-market secondary lens inserts, curved waveguide optics, headsets designed to fit over a user’s existing prescription glasses, and built-in mechanical myopia dials that allow the user to make adjustments. Clearly, the option to embed the display technology directly into prescription lenses will be preferred by daily glasses wearers and is expected to be the nominal path selected by AR/MR device manufacturers to make these devices more attractive to mainstream consumers.examples 

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However, incorporating custom optics into these devices for user prescription compensation means that a significant portion of devices are not identical. Any devices manufactured for a user with a vision prescription will not conform to a standard optical configuration. Vision prescriptions must correct for two main types of refractive errors: a user’s near-sightedness (myopia)/far-sightedness (hyperopia), and/or astigmatism. 

Vision errors are measured in diopters, within an normal range (majority of the population) of +6/-6 diopters for near/far-sighted refractive error and ±2.5D or less for astigmatism, out to two decimal points. This combination of eyesight variation and measurement ranges can result in thousands of possible unique Rx and thousands of permutations in device optics. Thus, the second challenge for device makers is how to perform effective quality testing for the wide variety of AR/MR device optics. 

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Quality Measurement of Rx AR/MR Device Displays

Accurate measurement and evaluation of visual performance characteristics such as MTF, uniformity, and distortion requires a display measurement system to compensate for the device’s corrective optics. For practical reasons, the measurement solution must also be efficient to test devices at production speed. One approach used for quality measurement of prescription XR devices is reverse compensation optics. Essentially, various lenses are used to reverse (zero out) the effect of the prescription, enabling the inspection solution to measure the device display as if it were a standard (non-prescription) device. Any image defects such as distortion can thus be easily identified using standard metrology software. 

This is a mechanical solution, requiring the reverse compensation lens or lenses to be placed between the entrance pupil of the camera and the DUT. Multiple moving parts can be required and there must be adequate space for configuration of an inspection station with multiple lenses (Figure 1). Additionally, this solution relies on foreknowledge of the user’s prescription so that the correct compensation lens(es) can be selected and mounted into the proper orientation.

A new approach has been developed that relies on a combination of patent-pending methods including a software-controlled electronic focus mechanism and an external adjustable lens. Used together, these novel methods enable accurate and efficient visual characterization of XR devices with a full array of prescription optics. There are two components of this solution, a Spherical Correction Method to address myopic/hyperopic vision, and a Cylindrical Compensation Method to address astigmatism. 

Learn more about the science of prescription optics for AR/MR devices, quality measurement approaches for these devices, and Radiant's novel, patent-pending solution for accurate and efficient prescription device display evaluation in the upcomging webinar: Quality Measurement of AR/MR Devices With Prescription Optics, hosted by GlobalSpec.  

In this presentaiton, Test Engineer Erin Brown describes the optical challenges faced by designers and manufacturers of prescription AR/MR devices and provides a review of current prescription lens compensation technology, including the benefits and challenges of this method. She will then present Radiant's novel, patent-pending solution that include both software-driven and hardware approaches to addressing spherical (myopic/hyperoptic) and cylindrical (astigmatic) prescription otpics in user devices. 

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CITATIONS

1. The Vision Council’s December 2021 VisionWatch Vision Correction and Frame reports.
2. World Report on Vision, World Health Organization, October 8, 2019.
3. Van Dam, A., “Why are these groups so much more likely to wear glasses than any others?”, Washington Post, (May 5, 2023). https://www.washingtonpost.com/business/2023/05/05/glasses-eyes-use-rising/
4. Ibid.
5. Mudditt, J., “Why short-sightedness is on the rise,” BBC (Oct 4, 2022). https://www.bbc.com/future/article/20220927-can-you-prevent-short-sightedness-in-kids
6. Sneha Mali, "Prescription Glasses Market Report 2024 (Global Edition)," Cognitive Market Research 8th Edition, CMR714463, Introduction (2024). https://www.cognitivemarketresearch.com/prescription-glasses-market-report