Approximately how many rod photoreceptors are in the human eye?

Approximately how many rod photoreceptors are in the human eye?

• A. 60 million
• B. 6 million
• C. 120 million
• D. 240 million

Answer: (C)

Rods are the photoreceptors responsible for vision in dim light and for detecting motion. In the human retina they outnumber cones by a large margin, with about 120 million rods compared with around 6 million cones. This abundance explains why peripheral vision is so sensitive in low light, while the center of the retina—the fovea—has a high concentration of cones for sharp, color vision. So, approximately 120 million rod photoreceptors best match what’s known about the human eye.

Rods are the photoreceptors responsible for vision in dim light and for detecting motion. In the human retina they outnumber cones by a large margin, with about 120 million rods compared with around 6 million cones. This abundance explains why peripheral vision is so sensitive in low light, while the center of the retina—the fovea—has a high concentration of cones for sharp, color vision. So, approximately 120 million rod photoreceptors best match what’s known about the human eye.