Homemade Protractors

After Thursday’s mid-morning tea break, we returned to the study of vision.  We discussed the retina and its photoreceptors.  To illustrate the different distribution of photoreceptors (rods and cones) in the eye, I had the monks make protractors by folding paper several times.  The monks then drew colored numbers, shapes or letters on popsicle sticks.  One monk held the protractor paper up to his face and another monk moved the popsicle stick from the peripheral vision to central vision of the monk holding the paper.  While the monk looked straight ahead, he was asked when he could see movement, shape, color and detail of the image on the stick.

We got back together to discuss the results.  In almost all cases, the monks could see movement and some shape in their peripheral vision, but to see color and detail, the stick needed to be in their central vision.  This demonstration shows how rod receptors are located primarily in the peripheral part of the retina and cone receptors are located in the central part of the retina.