What canthal tilt measures at the eye corners
Canthal tilt describes the slope of a line joining the inner and outer corners of an eye. The inner corner sits beside the nose; the outer corner sits toward the temple. In a front-facing photograph, comparing their heights gives an angle rather than a description of the whole eye. Eyelid curvature, eyebrow shape, eye opening and lashes can all change the visual impression without changing the two endpoints in the same way.
This calculator estimates those endpoints from facial landmarks and reports a separate angle for each eye. It does not trace eyeliner, use the end of an eyebrow as a corner, or measure how far the upper eyelid arches. Those distinctions matter when comparing the result with an impression from a mirror. A visibly lifted eyebrow does not necessarily imply a larger canthal tilt.
Think of the result as a description of two short lines in this particular portrait. It cannot summarize your expression, attractiveness, personality or eye health. Two people with the same measured angle can have very different eyelid shapes and overall appearances. The useful question is whether the corner positions were captured clearly enough to make the angle interpretable.
Eye tilt is also separate from eye spacing. Moving two otherwise identical eye outlines farther apart changes their spacing but leaves each corner-to-corner slope unchanged. Use the angle to answer an angle question, rather than treating it as a summary of the entire eye area.
Positive, neutral and negative tilt: reading the sign
Positive canthal tilt means the outer corner is higher than the inner corner after the tool accounts for sideways head lean. Negative tilt means the outer corner is lower. A neutral line is approximately horizontal in that corrected frame. These are geometric descriptions, not grades. The plus sign does not mean a better result, and a minus sign does not mean a problem.
For an illustrative reading, +5 degrees describes an upward slope toward the temple, 0 degrees describes a level line, and −5 degrees describes a downward slope. These examples explain the sign convention; they are not population averages, recommended targets or medically validated boundaries. This tool does not label a particular band as ideal. It also does not provide a validated normal range for age, sex or ancestry.
A small number close to zero deserves especially cautious interpretation. If one image gives +0.4 degrees and another gives −0.3 degrees, the sign changed but the underlying difference is tiny. Slight movement in a detected corner can explain that change. Treat near-zero results as approximately level rather than deciding that your eye changed category between photographs. The displayed decimal precision is not a guarantee of equivalent measurement accuracy.
How the calculator establishes horizontal and degrees
The calculation first converts landmark coordinates into image pixels, using both the image width and height. This matters because normalized horizontal and vertical coordinates do not represent the same number of pixels in a rectangular photograph. Using them directly could distort the angle. The tool then uses a forehead-to-chin line as a facial vertical reference and measures eye-corner positions relative to that line.
For each eye, the angle comes from the vertical difference between its inner and outer corners divided by their horizontal separation, converted through an arctangent into degrees. The sign is oriented consistently toward the outer corner on either side. In practical terms, an outer corner five pixels higher across a sixty-pixel horizontal span produces roughly +4.8 degrees. That is a worked mathematical example, not a target for a real eye.
Using the facial vertical reduces the effect of rolling your head toward one shoulder. It does not reconstruct a three-dimensional face or correct every camera angle. Turning toward one side or tipping your chin changes the projected geometry in a different way. The forehead and chin landmarks are themselves estimates, so an imperfect reference line can influence both eye readings.
Photographing eye corners without hiding the endpoints
Use a portrait with the camera facing you at eye height. Look straight ahead with a relaxed expression, keeping both inner and outer corners visible. Even light helps separate the eyelids from shadows. Avoid a strong squint or a raised-cheek smile for the reference image because these can make the corners harder to locate consistently. You do not need to force your eyes open unusually wide.
Glasses, heavy liner extending beyond the real corner, false lashes and hair can obscure the endpoints. If the estimate seems surprising, try an unobstructed photograph before interpreting the number. A crop that cuts off the forehead or chin can also weaken the reference used to compensate for head lean. Include the full face and enough surrounding space that the facial outline is visible.
Place the camera farther away than an extreme close-up and crop afterward if needed. Keep the same distance and camera position when comparing images. A camera above your head, a phone held to one side, or a portrait taken while you turn toward a window may create a different projection. Rotating the finished image can correct the canvas orientation, but it cannot recover a view that was never photographed straight on.
Why the two eye angles may differ
The tool reports the eyes separately because combining them into a single average would hide differences. A result of +3 degrees on one side and +6 degrees on the other is not equivalent to two eyes both measuring +4.5 degrees, even though their average is the same. Look at the individual readings and the conditions of the image before trying to explain the difference.
The labels refer to sides of the photograph. A selfie preview may be mirrored, and a saved image may use a different orientation from the preview. Confirm which visible eye corresponds to each label rather than assuming photograph-left always means your anatomical left. Mirroring can swap the labels; it does not make a genuinely upward corner line become a downward one under the tool's sign convention.
A difference can reflect visible facial variation, an uneven expression, head rotation or landmark estimation. The calculator cannot separate those causes from one picture. If the gap persists across a few comparable, clear portraits, you can describe it as a recurring photographic measurement. That still does not establish a clinical condition or explain why it exists. There is no validated asymmetry diagnosis built into these angle readings.
Comparing repeat photos without chasing an ideal angle
For a useful repeat check, take two or three photos in one sitting with the same camera, lighting and distance. Return to a relaxed pose between shots. Record each pair of angles alongside the image rather than keeping only the result you like best. If the values vary substantially, improve the photo setup before drawing conclusions about the shape of your eyes.
Suppose comparable photos show +4, +5 and +4 degrees for one eye. You can reasonably summarize those images as showing a similar upward slope, while leaving room for estimation error. If the sequence is −2, +7 and +1 degrees, a precise single-number description is less useful. Check whether the corners were obscured, whether the head turned, or whether the expression changed. The tool does not calculate a statistical confidence interval from these repeats.
For styling, use the angle as one observation alongside the curve of your eyelids and the effect you personally want. You can try different eyeliner directions or frame shapes without treating the natural angle as something to correct. Do not use this result to plan a procedure or infer a health issue. If your goal is simply to understand a photograph, a clear explanation of the corner line is more informative than searching for a universally perfect degree.