Blind Spot Activity Blind Spot Activity Materials Worksheet

Blind Spot Activity

Blind Spot Activity • Materials: – Worksheet – 1 3 x 5 inch index card – 1 Ruler – Pen and/or Pencil

Blind Spot Activity • Mark a dot and a cross on a card as shown. – Be sure the cross is on the right, and the dot is on the left

Blind Spot Activity • Hold the card at eye level, about arm’s length away with your right hand • Close your right eye and look directly at the cross with your left eye. • Notice that you can also see the dot. • Focus on the cross but be aware of the dot as you slowly bring the card toward your face.

Blind Spot Activity • Answer #1 on your worksheet

Blind Spot Activity • Now, hold the card in your left hand • Dot is now on the right side • Now close your left eye and look directly at the cross with your right eye. Move the card slowly toward your face

• Answer #2 on your worksheet.

• Try the activity again, this time rotating the card so that the dot is on top of the cross. • Answer #3 on your worksheet

Think About It • Answer #4 on your worksheet

Blind Spot Activity • As a variation on this blind spot activity, draw a straight line across the card, from one edge to the other, through the center of the cross and the dot. • Repeat the process with both eyes

Blind Spot Activity • Answer #5 on your worksheet

Think About It • Answer #6 on your worksheet

ANSWER • Notice that when the dot disappears, the line appears to be continuous, without a gap where the dot used to be. Your brain automatically "fills in" the blind spot with the image surrounding the blind spot. This is why you do notice the blind spot in your day-to-day observations of the world.

OPTIC NERVE • The optic nerve carries messages from your eye to your brain. This bundle of nerve fibers passes through one spot on the light sensitive lining, or retina, of your eye. In this spot, your eye's retina has no photoreceptors. When you hold the card so that the light from the dot falls on this spot, you cannot see the dot.

Cells that detect light Nerve bundle BLIND SPOT

Blind Spot Activity • In order to find the approximate size of your blind spot on your retina – We will assume that the retina is 2 cm from the pupil

Blind Spot Activity 1. Turn your index card over and mark a cross on the left edge. 2. Have your partner hold their pencil/pen on the right edge of the card. 3. Slowly bring the card toward your face and stop when the pen tip disappears 4. Measure the distance from eye to card (Your distance from the card is important in determining the size of your blind spot. Be sure it is accurate) Record this information in #7 a

Blind Spot Activity • Close your left eye and look directly at the cross with your right eye. • Have your partner move an pen tip around on the card until it disappears in your blind spot. • Mark, on the card, the places where the pen tip disappears. Trace the shape and size of your blind spot on the card. • Measure the diameter of the blind spot on the card. Record this in #7 b on your worksheet.

Blind Spot Activity • We know that the distance from your retina to your pupil is about 2 cm. Knowing that, we can use the following formula to find the size of your blind spot on your retina:

Blind Spot Activity • s = S(d/D), where – s = diameter of your blind spot on your retina (we are figuring this out) – S = distance from your retina to your pupil (2 cm) – d = diameter of your blind spot on the card – D = distance from your eye to the card

Blind Spot Activity • s = S(d/D), where – – • • s = diameter of your blind spot on your retina S = distance from your retina to your pupil d = diameter of your blind spot on the card D = distance from your eye to the card s = 2 cm (10 cm/25 cm) = 2 cm(0. 4) = 0. 8 cm My blind spot has a 0. 8 cm diameter Do the math in #8 on your worksheet Record the size of your blind spot on your retina in #9 on your worksheet