Canthal tilt: one angle, measured badly by one photo.

Canthal tilt is the angle of the line from the inner corner of the eye (near the nose) to the outer corner, measured against a horizontal reference across the face. Outer corner higher than inner corner is called positive tilt. Outer corner lower is negative. Roughly level is neutral. That's the whole definition — it's a geometry angle, not a diagnosis, and it isn't tied to eye color, eye size, or eyelid shape.

Canthal tilt is defined relative to a horizontal line across the face — which means it's directly sensitive to how level the head is in the photo, not just to the eyes themselves. Tilt your chin down a few degrees, turn slightly off-axis, or hold the camera a little high or low, and the apparent angle between the eye corners shifts even though nothing about your eyes changed. Of the six ratios Mogalytics tracks, eye-line tilt is one of the more head-angle-sensitive — see the full breakdown of why scores swing between scans for the other camera variables that move a reading the same way. A single uploaded photo has no way to correct for this; whatever head angle existed in that one frame is baked into the result.

The fix isn't a better single photo, it's ruling out head angle as the variable before trusting the number. Hold distance, light, and expression steady, keep the head level and facing the lens straight-on, and take more than one reading — the practice guide covers framing and pose in more detail. If the angle still moves between attempts once head position is controlled for, that's a more meaningful signal than one photo can ever give you.

Mogalytics tracks eye-line tilt as one of six weighted geometry ratios — alongside jaw ratio, frame symmetry, midface, cheek ratio, and bridge — settled over a 30-frame trimmed-mean window so a single head turn doesn't define the result. It's read live from your own camera on-device, not from one uploaded photo, so you can hold your head level, check the read, adjust, and check again in the same session instead of guessing from a single shot. See what the full composite tier actually means once you have a stable reading, and how to track it across sessions rather than trusting any one scan.

Canthal tilt is one piece of a six-measurement composite. If you're auditing the rest: the facial symmetry test is thrown off by head turn and tilt the same way; midface ratio is distorted by camera distance instead of angle; and the nose bridge ratio is the most angle-sensitive of the rest since it's the most forward-projecting structure Mogalytics measures.