Why can't I see stereograms?

Most people who cannot see a stereogram yet are a small adjustment away. Work through the causes below in order. If none of them help, the last section explains stereo blindness, which affects a minority of people and has nothing to do with effort.

1. The image is scaled

A stereogram only works at the size it was made for. A zoomed page, a stretched image or a phone shrinking a large picture changes the repeat width. Reset your browser zoom to 100 percent. On this site the puzzle is served in a size that fits your screen at its native pixels.

2. You are focusing on the screen

Normal reading focus is the habit to break. Your eyes must point past the screen while the picture stays sharp. Start with your face close, so focusing on the screen is impossible, then lean back slowly without changing where your eyes point.

3. You are not using the guide dots

The two dots above each puzzle are one repeat apart. When your eyes are set correctly they merge into three dots. Watching the dots gives you feedback while you adjust; once you see three, the hidden picture is already there.

4. You are crossing your eyes

Crossing your eyes shows the picture sunk in and can feel harder to hold. See parallel vs cross-eyed viewing for both methods.

5. Glasses, light and screen

• Keep your normal glasses on.
• Reduce glare: turn down room lights or tilt the screen.
• A laptop or desktop screen is easier while learning than a phone.
• Give it a full minute. The first success often takes longer than every one after.

6. Start easier

Begin with the practice lessons: step 2 is a huge square at extra depth, the easiest image on the site. Then try a few closed weeks in the archive, where the answer is shown so you know what to look for.

Stereo blindness

Seeing depth in a stereogram needs stereo vision, the brain's comparison of what each eye sees. Some people have little or none of it, often because of a lazy eye (amblyopia), a squint (strabismus) in childhood, or a large difference in prescription between the eyes. Published estimates of stereo blindness range from about 3 percent to over 10 percent of people, depending on the test. If that is you, the hidden picture will not appear however long you look. The archive, lessons and leaderboards remain open to you, and an eye care professional can test your stereo vision if you want to know for sure.