Click to set fixation, or upload a panoramic image and enter fullscreen to pan the scene. The + marks where you look; masks follow your gaze at your calibrated distance.
Image
Panoramic images (wide aspect) fill the height and scroll horizontally in fullscreen.
Eye
Run the mapper to replace the textbook blind spot with yours.
Cover one eye. Stare at the + and don't let your eye wander toward the dots. Whenever a dot appears anywhere, press space or click. Dots you never see are the ones landing on your optic disc.
Test
Result
1 · Pixels per centimetre
Hold any bank card against the screen and drag until the box is exactly as wide as the card (85.6 mm).
2 · Viewing distance
Measure from your eye to the screen and keep it there while using either tool. Everything is in visual degrees, so this number is what makes the geometry true.
Why this matters
The blind spot sits about 15° from where you're looking, on the temporal side (away from your nose), and is roughly 7.5° wide by 5.5° tall — about nine full moons could hide in it.