Apple Vision Pro Part 6 – Passthrough Mixed Reality (PtMR) Problems


I planned to wrap up my first pass coverage of the Apple Vision Pro (AVP) with my summary and conclusions based on prior articles. But the more I thought about it, Apple’s approach to Passthrough Mixed Reality (PtMR) seems like it will be so egregiously bad that it should be broken out and discussed separately.

Apple Prioritized EyeSight “Gimmick” Over Ergonomics and Functionality

There are some features, particularly surrounding camera passthrough, where there should have been an internal battle between those who wanted the EyeSight™ gimmick and what I would consider more important functionality. The backers of EyeSight must have won and forced the horrible location of the passthrough cameras, optical distortion from the curved glass in front of all the forward-facing cameras and sensors, put a fragile piece of hard-to-replace glass on the front where it can be easily scratched and broken, and added weight to the front were it is least desired. Also, as discussed later, there are negative effects on the human visual system caused by misaligning the passthrough cameras with the eyes.

The negative effects of EyeSight are so bad for so many fundamental features that someone in power with little appreciation for the technical difficulties must have forced the decision (at least, that is the only way I can conceive of it happening).  People inside the design team must have known it would cause serious problems. Supporting passthrough mixed reality (PtMR) is hard enough without deliberately creating problems.

Meta Quest 3 Camera Location

As noted in Meta Quest Pro (Part 1) – Unbelievably Bad AR Passthrough, Meta is locating the soon-to-be-released Quest 3 main passthrough camera closer to the center of view of the eyes. Fixed cameras in front of the eyes won’t be perfect and will still require digital correction for better functional use. It does appear that Meta is taking the PtMR more seriously than it did with the Meta Quest Pro and Quest 2.

I’m going to be looking forward to getting a Meta Quest 3 to test out when it is released soon.

Definitions of AR/VR/MR and PtMR

The terms used to describe mixed reality have been very fluid over the last few years. Before the introduction of Hololens, Augmented reality meant any headset that displayed virtual content on a see-through display. For example, just before Hololens went on sale, Wired in 2015 titled their article (with my bold emphasis): Microsoft Shows HoloLens’ Augmented Reality Is No Gimmick. With the introduction of Hololens, the term “Mixed Reality” was used to distinguish AR headsets with SLAM to lock the virtual to the real world. “AR” headsets without SLAM are sometimes called AR Heads-Up Displays (HUDs), but these get confused with automotive HUDs. Many today refer to a see-through headset without SLAM as “AR” and one with SLAM as “MR,” whereas previously, the terms “AR” covered both with and without SLAM.

Now we have the added confusion of optical see-through (e.x. Hololens) and camera passthrough “Mixed Reality.” While they may be trying to accomplish similar capabilities, they are radically different in their capabilities. Rather than constantly typing “passthrough” before MR, I abbreviated it as PtMR.

In Optical AR, the Virtual Content Augments the Real World – With PtMR, the Real World Augments the Virtual Content

Optical MR prioritizes seeing the real world at the expense of the virtual content. The real world is in perfect perspective, at the correct focus distance, with no limitation by a camera or display on brightness, with zero lag, etc. If done well, there is minimal light blocking and distortion of the real world and little blocking of the real-world FOV.

PtMR, on the other hand, prioritizes virtual image quality at the expense of the real world, both in how things behave in 3-D space (focus perspective) and in image quality.

We are likely many decades away, if ever, from passing what Douglas Lanman of Meta calls their Visual Turing Test (see also the video linked here).

Meta’s demonstrations at Siggraph 2023 of their Flamera with perspective-correct passthrough and Butterscotch with vergence accommodation conflict served to show how far PtMR is from optical passthrough. They can only address each problem individually, each with a large prototype, and even then, there are severe restrictions. The Flamera has a very low-resolution passthrough, and Butterscotch only supports a 50-degree FOV.

It is also interesting that Butterscotch moves back from Half Dome 3’s electronic LCD variable focus to electro-mechanical focusing to address VAC. As reported in Mixed Reality News, “However, the technology presented problems with light transmission and image quality [of the electronic LCD approach], so Meta discarded it for Butterscotch Varifocal at the expense of weight and size.”

All of this work is to try and solve some of the many problems created by PtMR that don’t exist with optical MR. PtMR does not “solve” the issues with optical MR. It just creates a long list of massively hard new problems. Optical AR has issues with the image quality of the virtual world, very large FOV, and hard-edge occlusion (see my article Magic Leap 2 (Pt. 3): Soft Edge Occlusion, a Solution for Investors and Not Users). I often say, “What is hard in optical MR is easy in PtMR and vice versa.”

Demo or Die

Meta and others seem to use Siggraph to show off research work that is far from practical. As stated by Lanman of Meta, of their Flamera and Butterscotch VAC demos at Siggraph 2023, Meta’s Reality Labs has a “Demo or Die” philosophy. They will not be tipping off their competition on concepts they will use within a few years. To be clear, I’m happy to see companies showing off their technical prowess, but at the same time, I want to put it in perspective.

Cosmetic vs. Functional Passthrough PtMR

JayzTwoCents video on the HTC Vive XR Elite has a presentation by Phil on what he calls “3D Depth Projection” (others refer to it as “perspective correct“). In the video (sequence of clips below), Phil demonstrates that because the passthrough video was not corrected in scale, position, and perspective in 3-D space, it deprives him of hand-eye coordination to catch a bottle tossed to him.

As discussed in Meta Quest Pro (Part 1) – Unbelievably Bad AR Passthrough in the section The method in the Madness: MQP prioritizes 3-D spatial over image quality.

Phil demonstrated in the video (and in a sequence of clips below) that with the Meta Quest Pro, even though the image quality is much worse and distorted due to the 3D projection, he can at least catch the bottle.

I would classify the HTC Vive XR Elite as having a Cosmetic Passthrough.” While the image quality is better (but still not very good), it is non-functional. While Meta Quest Pro’s image quality is lousy, it is at least somewhat functional.

Something else to notice in the MQP frame sequence above is that there are both lag and accuracy errors in hand tracking.

Effects on Vision with Long-Term Use

It is less obvious that the human visual system will start adapting to any camera placement and then have to re-adapt after the headset is removed. This was briefly discussed in AVP Part 2 in the section titled Centering correctly for the human visual system, which references Steve Mann in his March 2013 IEEE Spectrum article, “What I’ve learned from 35 years of wearing computerized eyewear.” In the early days with Steve Mann, they had no processing power to attempt to move the effect of the camera images digitally. At the same time, I’m not sure how well the correction will work or how a distorted view will affect people’s visual perception during and after long exposure. As with most visual effects, it will vary from one individual to another.

Meta Flamera Light Field Camera at Siggraph 2023

As discussed in AVP Part 2 and Meta Quest Pro (Part 1) – Unbelievably Bad AR Passthrough, having the passthrough cameras as close as possible to being coaxial to the eyes (among other things) is highly desirable.

To reduce any undesired negative effects on human vision caused by cameras not aligning with the eyes, some devices, such as the Quest 2 and Quest Pro from Meta, use processing to create what I will call “virtual cameras” with a synthesized view for each eye. The farther the physical cameras are from the eye’s location, the larger the correction will be required and the larger the distortion in the final result.

Meta at Siggraph 2023 presented the paper “Perspective-Correct VR Passthrough Without Reprojection” (and IEEE article) and showed their Flamera prototype with a light field camera (right). The figure below shows how the camera receives light rays from the same angle as the eye with the Light Field Passthrough Camera.

Below are a couple of still frames (with my annotations) from the related video that show how, with the Meta Quest 2, the eye and camera views differ (below left), resulting in a distorted image (below right). The distortion/error as the distance from the eye decreases.

It should be noted that while Flamera’s light field camera approach addresses the angular problems of the camera location, it does so with a massive loss in resolution (by at least “n,” where n is the number of light field subviews). So, while interesting in terms of research and highlighting the problem, it is still a highly impractical approach.

The Importance of “Perspective Correct” PtMR

In preparing this article, I returned to a thread on Hacker News about my Meta Quest Pro (Part 1) – Unbelievably Bad AR Passthrough article. In my article, I was trying to explain why there was a “The method in the Madness: MQP prioritizes 3-D spatial over image quality” of why Meta was distorting the image.

Poster Zee2 took exception to my article and seemed to feel I was understating the problem of 3-D perspective. I think Zee2 missed what I meant by “pyrrhic victory.” I was trying to say they were correct to address the 3D depth issue but that doing so with a massive loss in image quality was not the solution. I was not dismissing the importance of perspective-correct passthrough.

Below, I am copying his comment from that thread (with my bold highlighting)), including a quote from my article. Interestingly, Zee2 comments on Varjo having good image quality with its passthrough, but it is not perspective-correct.

I also really don’t know why he [refering to my article] decided to deemphasize the perspective and depth correctness so much. He mentions it here:

>[Quoting Meta Quest Pro (Part 1) – Unbelievably Bad AR Passthrough] In this case, they were willing to sacrifice image quality to try to make the position of things in the real world agree with where virtual objects appear. To some degree, they have accomplished this goal. But the image quality and level of distortion, particularly of “close things,” which includes the user’s hands, is so bad that it seems like a pyrrhic victory.

I don’t think this is even close to capturing how important depth and perspective correct passthrough is.

Reprojecting the passthrough image onto a 3D representation of the world mesh to reconstruct a perspective-correct view is the difference between a novelty that quickly gives people headaches and something that people can actually wear and look through for an extended period of time.

Varjo, as a counterexample, uses incredibly high-resolution cameras for their passthrough. The image quality is excellent, text is readable, contrast is good, etc. However, they make no effort to reproject their passthrough in terms of depth reconstruction. The result is a passthrough image that is very sharp, but is instantly, painfully, nauseatingly uncomfortable when walking around or looking at closeup objects alongside a distant background.

The importance of depth-correct passthrough reprojection (essentially, spacewarp using the depth info of the scene reconstruction mesh) absolutely cannot be understated and is a make or break for general adoption of any MR device. Karl is doing the industry a disservice with this article.

From: Hacker News Meta Quest Pro – Bad AR Passthrough comment by Zee2 

Does the AVP have Cosmetic or Functional PtMR or Something Else?

With the AVP’s passthrough cameras being so poorly located (thanks to EyeSight™), severe distortion would seem inevitable to support functional PtMR. I don’t believe there is some magic (perhaps a pun on Magic Leap) that Apple could employ that Meta couldn’t that would simultaneously support good image quality without serious distortion with the terrible camera placement due to the Eyesight(tm) feature.

So, based on the placement of the cameras, I have low expectations for the functionality of the AVP’s PtMR. The “instant experts” who got to try out the AVP would be more impressed by a cosmetically better-looking passthrough. Since there are no reports of distortion like the MQP, I’m left to conclude that, at least for the demo, they were only doing a cosmetic passthrough.

As I often say, “Nobody will volunteer information, but everyone will correct you.” Thus, it is better to take a position based on the current evidence and then wait for a correction or confirmation from the many developers with AVPs who read this blog.


I’m not discounting the technical and financial power of Apple. But then I have been writing about the exaggerated claims for Mixed Reality products by giant companies such as Google, Meta, and Microsoft, not to mention the many smaller companies, including the over $3B spent by Magic Leap, for the last ten years. The combined sunk cost of about $50B of these companies, not including Apple. As I’m fond of saying, “If all it took were money and smart people, it would already be solved.

Apple doesn’t fully appreciate the difficulties with Passthrough Mixed Reality, or they wouldn’t prioritize the EyeSight gimmick over core capabilities. I’m not saying the AVP would work well for passthrough AR without EyeSight, but it is hard enough without digging big technical holes to support a novelty feature.

Karl Guttag
Karl Guttag
Articles: 244


  1. In your concluding paragraph, I think the second sentence makes the first untrue. My feeling is that Apple knew they couldn’t make the AVP’s passthrough (or weight and weight distribution) actually good for any amount of money, so why not trade off very bad for worse and at least get an on-brand differentiating feature instead?

    It seems like a canny decision to me. It doesn’t appeal to me, but I’m not in their market.

  2. Karl, just wanted your take on this as it seems you are most knowledagle on this subject: Seems like Quanta Computers, a supplier for Apple, left Lumus to now partner with Vuzix for smart glasses products for global customers using waveguides and components sourced from Vuzix. Just wanted to know your best guess as to why they shifted from Lumus to Vuzix. I know Vuzix opened up a new facility to increase their manufacturing capabilities as well as developed a new tech that eliminates the eye glow on their diffractive waveguides, but there has to be more to it than that I’m sure.

    • Quanta makes optical systems/components for many companies. Quanta supplies many companies and works with many companies. It is not an either-or situation.

      You are talking dramatically different optical systems in terms of capabilities between Lumus and Vuzix. You have to look at the FOV, brightness, and other factors.

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