Blind Spot

Students use a simple card with a dot and an X to locate their blind spot. By covering one eye and moving the card at arm’s length, they observe how part of their vision disappears when light falls on the optic nerve instead of light-sensitive cells in the retina.

1. Give each student a 3 x 5 inch card (or other stiff paper) and a black marker.
2. Instruct students to draw a dot on the left side of the card and an X on the right side.
3. Hold the card at arm’s length, with the X on the right.
4. Close the right eye and look at the X with the left eye while staying aware of the dot.
5. Slowly move the card closer to the face until the dot disappears, then reappears.
6. Repeat by closing the left eye, looking at the dot with the right eye, and noticing when the X disappears.
7. Draw a straight line connecting the dot and the X with a ruler.
8. Repeat the activity; this time the brain fills in the missing part of the line, creating the illusion of a continuous line.

Quick Blind Spot Test - Vision Vibes:

📄 Blind Spot- American Academy of Ophthalmology: https://www.aao.org/museum-eye-openers/experiment-blind-spot

• Try using different shapes or colors instead of a dot and an X to see if the blind spot effect changes.
• Test at different distances to compare how far away the card can be while still making the dot or X disappear.
• Use both eyes open to observe how one eye compensates for the other’s blind spot.

• Do not press objects into the eyes while performing the activity.
• Avoid straining vision by taking breaks if eyes become tired.
• Ensure students do not draw markers too close to their faces when testing.

• Why does the dot or X disappear at certain points? (Because the image falls on the optic nerve, where there are no light-sensitive cells.)
• Why don’t we normally notice our blind spot? (The brain fills in the gap, and the other eye compensates when both eyes are open.)
• What happens when a line is drawn between the dot and X? (The brain fills in the missing section, creating the illusion of a continuous line.)
• What does this activity reveal about how the brain processes vision? (It shows that vision is not just input from the eyes but also interpretation by the brain.)