According to a topographic map, the highest rod density is a ring encircling the fovea at what eccentricity?

According to a topographic map, the highest rod density is a ring encircling the fovea at what eccentricity?

• A. 10 degrees
• B. 20 degrees
• C. 25 degrees
• D. 30 degrees

Answer: (B)

Rods are not evenly spread across the retina. The fovea—the center of the visual field—has very few rods and is dominated by cones to support sharp, detailed color vision. As you move away from the fovea, rods become more numerous and reach a maximum density in a ring surrounding the fovea. This peak occurs at a moderate distance from the center, not too close and not at the far edge of the retina. After that ring, rod density gradually decreases as you go further into the periphery. So the ring of highest rod density is located at about twenty degrees of eccentricity from the fovea.

Rods are not evenly spread across the retina. The fovea—the center of the visual field—has very few rods and is dominated by cones to support sharp, detailed color vision. As you move away from the fovea, rods become more numerous and reach a maximum density in a ring surrounding the fovea. This peak occurs at a moderate distance from the center, not too close and not at the far edge of the retina. After that ring, rod density gradually decreases as you go further into the periphery. So the ring of highest rod density is located at about twenty degrees of eccentricity from the fovea.