Canthal tilt

Canthal tilt is the angle of the line running from the inner corner of the eye to the outer corner, measured against the horizontal. It is positive when the outer corner sits higher than the inner one, negative when it sits lower, and neutral when the two are level. The oculoplastic literature puts the usual adult range at roughly two to eight degrees positive, with some variation by ancestry and a slight difference between a person's own two eyes being normal. The angle is set by where the canthal tendons anchor to the orbital bone, which is why nothing non-surgical changes it. What does change is how it reads: under-eye puffiness, brow position and — more than either — camera height. A phone held below eye level flattens or reverses the apparent tilt, which is why most negative readings from selfies are the photograph rather than the eye.