PD Tool Not Working? Fixes for Every Common Error

Last updated: October 2026 | Reading time: 7 minutes

Short answer: almost every error from an online PD tool comes from one of five things: the card is not fully visible, your head is turned or tilted, you are not looking at the lens, glare or shadow hides your eyes, or the camera is blocked. Find your message below.

"Unable to detect your credit card"

The tool could not find a rectangle with the proportions of a bank card.

• Make sure all four corners are visible and nothing, including your fingers or hair, covers the edges.
• Use contrast: a dark card on a light wall, or a light card against a dark background.
• Lay the card flat against your forehead. A card tilted toward or away from the camera looks the wrong shape.
• Avoid shiny cards under strong light: glare can wipe out an edge.

"The calibration card appears angled or partially detected"

The width-to-height ratio of what the tool found is outside the range of a real card, which usually means the card is tilted. Press it flat, keep the top edge level, and retake.

"Head is turned too far to the side"

When your head turns, the horizontal gap between your eyes shrinks in the image, so the tool rejects turns of more than about 6°. Square your shoulders to the camera and aim your nose at the lens.

"Head is tilted" / "Please look directly at the camera"

Roll (ear toward shoulder) and pitch (chin up or down) change how the face is projected. Level your head and keep the phone at eye level.

"Your eyes appear to be looking away from the lens"

For distance PD you need to look at the camera lens, not the screen or the card. If the message persists, close your eyes, open them, and focus on the lens itself.

"Eyes closed / glare / low light" warnings

• Open both eyes fully; blinking before the shot is the usual cause.
• Move away from a window or lamp that reflects in your eyes.
• Add front light if your face is in shadow.

"Measurement is outside the expected PD range"

The result was far from a believable adult PD, so something earlier is wrong, most often the card. Retake with the entire card in the frame and your face centred. If you consistently get a real but unusual value, ask an optician to confirm it.

Camera does not start

• Allow camera permission in the browser's site settings.
• Close other apps that use the camera (video calls).
• Use the upload option with a photo from your phone's camera app.
• Try a different browser. Camera access needs a secure (HTTPS) page.

Values change a lot between photos

Variation means something is changing between shots: distance to the camera, head angle, or card position. Rest your elbows on a table, take three photos, and compare. If they agree to within about 1 mm, trust the average. If not, retake in more even light.

Still stuck?

If the photo looks fine and the number still seems wrong, see an optician. A real measurement is also the right choice for progressive lenses and high prescriptions. Related reading: common PD measurement mistakes, how to measure PD with a credit card, how to measure PD with a phone camera.