The optical architecture of VR/AR devices usually puts the image plane of the display 1.5 – 2.0 meters from the eyes, whilst stereoscopy is used to give an impression of depth. The resulting mismatch in where the crystalline lens of the eye focuses (accommodation) and the vergence of the eye, is unnatural to the visual system and causes an imbalance that can lead to nausea. Developer guidelines from manufacturers advise against placing content closer than the image plane to avoid VAC induced discomfort. A similar problem is more apparent with AR headsets, where content shown on the display is not in focus if the eyes are focused on a real-world target closer than about 1.5 meters. This focal rivalry presents challenges for the many new applications utilising hand tracking to stimulate interaction with virtual objects. Focus tuneable lenses can be used to move the focal plane of the display to match the plane of accommodation. This presentation will compare the approaches to mitigate VAC and assess focus tuneable lenses in more detail, along with some details of a study using voice-coil actuated Alvarez lenses.
Optical systems for AR/VR headsets are designed for those who do not require vision correction. The reality, however, is that around 60% of the population have an ophthalmic prescription, and users generally prefer not to wear eyeglasses under a headset. This results in the user experience being compromised optically when compared to the design intent, even when the device has been designed with additional space to allow for glasses to be worn underneath. AR/VR devices are being engineered with high resolution displays and the optics optimised to for MTF, however with very little refractive error, the user will not be able to resolve such detail. Therefore, prescription correction is required for most users to be able to experience most new VR & AR devices as per their design. Market research suggests the limitations of current VR devices suggest that the very few understand their vision or know their prescription and fewer are aware of existing prescription correction solutions. This presentation discusses the advantages and disadvantages of prescription correction solutions for dedicated and shared use cases.
Head-mounted display (HMD) technologies are improving in resolution and brightness, but are not generally solving three key issues of prescription, accommodation and presbyopia. Eyeglasses worn within head-mounted devices reduce their optical quality, eyetracking efficacy, and comfort, they add stray light/reflections and increase bulk. Fixed inserts are more compact, but require many stock keeping units (SKU's), are incompatible with shareability, and have achieved a low market share. Adjustable lenses present a low SKU, integrated, on-demand solution to these issues, but with some remaining technology challenges. We show how the spherical optics adjustable non-round fluid-filled lens may be extended to general ophthalmic prescriptions by the inclusion of astigmatism correction on an arbitrary axis. We also describe methods to produce the long lifetime fluid-filled lens with an anti-reflective surface. Finally, we define the rules for building a minimal thickness and weight liquid lens.
We present a varifocal system for generating consistent accommodation cues and providing prescription correction in Virtual Reality Head-Mounted Displays (VR HMDs). The proposed approach mitigates the Vergence-Accommodation Conflict (VAC), a fundamental cause of discomfort in today’s VR, and eliminates the need for corrective eyeglasses inside head-mounted displays. We augment traditional objective lenses with a focus-adjustable optical system based on Alvarez lenses, and demonstrate a proof-of-concept integration into a commercial mobile VR headset. This paves the way to lighter, thinner, and more comfortable headsets, enabling the prolonged use of VR with minimal visual discomfort.
Adjustable lens technology has the potential to improve Head Mounted Displays (HMDs) through style and comfort by providing optical prescription correction and focussing mechanisms integrated within the HMD. It can also reduce simulator sickness and user experience of 3D through resolution of Vergence Accommodation Conflict, and age-related user problems (presbyopia). We review the available technology and the design constraints to show how a fluid filled lens may be appropriate for AR and MR, and an Alvarez lens may be appropriate for VR.
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