Most people have a dominant eye, and aiming/pointing defer to it

What it is

When a task requires compressing directional information from both eyes into a single sighting line or pointing direction — looking at a distant target through a small hole, pointing a finger at an object, looking through a single eyepiece — most people unconsciously and consistently rely on one eye's positional information to make that judgment. That eye is called the dominant eye (also "sighting eye"). This has no necessary relationship to which eye has better visual acuity, nor is it the same as which eye's image is "more readily conscious" during ordinary two-eyes-open viewing (that's a different, rivalry-based sense of dominance). The dominance discussed here refers specifically to the eye that gets systematically favored whenever a task requires selecting a single direction or single line of sight.

Why it happens

In everyday viewing, what both eyes see is mostly fused and jointly presented, with no question of one eye "winning." But once a task inherently calls for a single direction (aiming, pointing, looking through a monocular eyepiece), the visuomotor system has to pick one of the two eyes' direction cues as the final output — it can't superimpose or average the two directions the way content fusion does, because the two direction cues already differ slightly (a consequence of the physical separation between the eyes), and simply averaging them would produce an aiming result that's systematically off from what either eye would have produced sighting alone. Most people's visuomotor systems have a stable default choice here, consistently using one eye's directional information as the final output, and that eye is what shows up as that individual's dominant eye. This preference is typically stable and repeatably measurable within the same person, though it remains unsettled whether its exact cause maps directly onto lateralized function in one cerebral hemisphere — what's been observed is simply that most people show this kind of consistent preference, and there is no fixed correspondence between which eye is preferred (or whether a preference exists at all) and handedness.

Studying it

• Sighting dominance test: having a participant form a small aperture with both hands, or hold up a card with a hole in it, and sight a distant target through it, then covering the left and right eye in turn to see which eye, when open, keeps the target centered in the aperture — that eye is the dominant one. A related variant has the participant point a finger at a target and then checks each eye in turn (a variant of the Miles test).
• Typical independent variables: task type (sighting versus perceptual dominance during ordinary two-eyed viewing), number of test repetitions, target distance.
• Typical dependent variables: test-retest consistency of the dominance result, whether the dominant eye matches handedness, and whether the sighting-dominance result agrees with other types of "dominance" measures (such as which eye tends to dominate more in binocular rivalry).
• Use in device/interface research: this kind of test is commonly used on devices that need monocular calibration (monocular sighting scopes, monocular near-eye displays) to determine which eye a participant should be aligned or calibrated to, rather than assuming by default that every user relies on the same eye.

Where it stops holding

• Not everyone shows a clear, stable dominant eye; some people get inconsistent results across repeated tests, or show only a very weak preference between the two eyes — it can't be assumed that every user can be cleanly sorted into "left-eye dominant" or "right-eye dominant."
• Sighting dominance and the eye that tends to temporarily dominate in binocular rivalry are "dominance" measured by two different methods, and the two don't necessarily agree — the result of one test shouldn't be treated as a stand-in for the other.
• There is no fixed, necessary correspondence between ocular dominance and handedness; ocular dominance can't be inferred from known handedness alone and needs to be measured separately.

Applying it

• For devices meant to be used with one eye (monocular smart glasses, monocular-sighting augmented reality, instruments viewed through a single eyepiece), if the optical design assumes the user will consistently use one particular eye, build a simple sighting-dominance test into the setup flow and have the device or onboarding adjust accordingly, rather than defaulting to assuming everyone uses the right eye or the left.
• For tasks requiring precise aiming or pointing (precise pointing interactions in augmented reality, monocular-sighting interactions), prefer aligning content to the user's dominant eye to reduce the systematic aiming offset introduced by forcing the use of the non-dominant eye.
• Verification: before finalizing a device's monocular calibration scheme, actually measure the distribution of ocular dominance in the target user population with a simple sighting test, rather than assuming a fixed ratio (such as the commonly cited figure that most people favor the right eye) applies directly to your own user base.

Related

• Same group: A1.33.1 Conflicting binocular input can produce rivalry instead of fusion · A1.33.3 Occluding one eye does not switch off its input, and rivalry can still occur · A1.33.4 Failure of binocular fusion produces diplopia or monocular suppression
• Nearby: A8 Motor Control
• Search terms: ocular dominance · sighting dominance · Miles test · eye dominance