Content outside the binocular overlap is seen by only one eye

What it is

Left and right images in a headset overlap only through a central band. Inside that band both eyes see the same content, fusion is possible, stereo can be read. Outside it lies a monocular crescent — only one eye sees it. UI placed in the crescent is not “a little off to the side”; it never had a second eye: no disparity, no fused backup, and if that eye is blocked or tired the patch vanishes. Binocular overlap is the jointly governed region, not the outer frame of the panel.

Why it happens

Each eye has its own optical field; the two intersect ahead of the face, and the width of that intersection is the overlap. On consumer headsets overlap is often well short of the advertised total field, leaving a crescent on each outer side. Pixels in the crescent drive one eye only, so stereo matching cannot occur, type loses the other eye’s redundancy, and contrast sensitivity has only one optical path. Ocular dominance makes one crescent feel more “present” than the other: content that enters only the non-dominant eye can subjectively fail to appear. Closing one eye, a fogged lens, or lashes at the rim kill the crescent before they kill the overlap. Putting anything that needs fusion or stable reading into the crescent hands it to a single channel that can drop at any time.

Studying it

Have people view the same edge elements binocularly, left-only, and right-only, and report what remains. Then measure stereoacuity and letter identification in overlap versus crescent.

Independent variables: element in overlap or crescent, which crescent, whether that side is the dominant eye. Dependent variables: detection under monocular viewing, whether a stereo judgement is even possible, reading accuracy, a rating of “this side went empty”.

An eye patch is closer to real occlusion than software-blanking one eye. Overlap width moves with IPD and fit; measure across people and donning, not on one centred, well-fitted wearer.

Where it stops holding

When overlap nearly equals total field, the crescents are thin and the constraint weakens. For monocular users (amblyopia, an occluded eye) the entire view is a “crescent”; overlap talk is meaningless and layout follows the remaining field. Vertical overlap is usually a smaller issue than horizontal — top and bottom are more often cropped together than staggered. World-locked scenery that spills into a crescent is often acceptable because landscape does not need fusion; controls are not.

Applying it

• Keep type, stereo depth, and controls that must stay visible inside the binocular overlap. At most, put non-stereo presence colour in the crescent.
• On the target headset, cover each eye and draw the crescents; pull the left and right layout bounds inside the overlap. Do not trust total field on the spec sheet.
• Do not split paired left/right information (left channel / right tool) into the two crescents — occlude one side and the pair is missing a half.
• How to check: after a task, cover the left eye, then the right, and look at the UI. Any piece that vanishes or becomes inoperable under one eye was not in the overlap.

Related

• Same group: N3.07.1 Edge content needs a head turn to be seen clearly · N3.07.2 Critical information must not sit at the edge · N3.07.3 The edge is fit for presence cues · N3.07.4 Pull edge elements inward to leave margin for optical falloff · N3.07.5 A ring layout fits the shape of the field of view better than a rectangle · N3.07.7 Elements that enter and leave the view with head motion need hysteresis or they flicker
• Nearby: N1.03 Field of View · N1.10 Binocular Disparity and Vergence–Accommodation Conflict
• Search terms: binocular overlap · monocular crescent · stereo overlap