Answer · Eye area
How do you measure canthal tilt?
Take a straight-on photo at eye level, then draw a line from the inner corner of each eye to the outer corner and compare it with a horizontal. Outer corner higher is positive, level is neutral, lower is negative. A photo can honestly show that direction, but not a precise angle, because head roll and camera height shift the slope.
Inner corner → outer corner. These drawings explain direction; they are not a measurement of a face.
Step by step
- Set up the photo. Camera exactly at eye height, phone at arm's length or further, even front light. Look straight into the lens with a relaxed face and relaxed brows.
- Level the head. Both ears, or both pupils, should sit at the same height. A head tipped toward one shoulder raises one outer corner and lowers the other.
- Find the corners. The inner corner, the medial canthus, is where the upper and lower lids meet by the nose. The outer corner, the lateral canthus, is where they meet at the side, not where eyeliner or lashes end.
- Draw the lines. Join inner to outer corner on each eye and compare each line with a horizontal through the inner corner.
- Read the direction. Clearly up is positive, a little up is slightly positive, flat is neutral, down is negative. Do it for both eyes separately.
The canthal tilt test does the same thing with a face mesh in your browser: it levels the head first, finds the corners and reports a band for each eye.
Why a photo cannot give an angle
The tilt is a small slope, and the camera adds its own. A camera above eye level with the chin dropped makes eyes read upturned; a camera below makes them read downturned. A close lens bends the outer face, and looking up or down moves the lids over the corners. Each of those shifts the apparent slope by more than real tilts differ between most people. So any app that gives you a precise number from a selfie is reporting partly your face and partly the camera. BecomeTen reports a band, as its methodology requires. Why do I look different in photos? covers the same lens effects across the whole face.
How to read the result
Slightly positive is the ordinary adult case. Neutral reads level and balanced; clearly positive reads alert. If a careful photo reads negative, retake it once to rule out a rolled head, then see is a negative canthal tilt bad?. If the two eyes land in different bands, that is either a small head roll or a genuine slight asymmetry, and a second photo will tell you which. The tilt is structural, so the band should hold across honest photos; can you change your canthal tilt? covers what shifts how it reads.