Under Scotopic vision, acuity is what value?

Under Scotopic vision, acuity is what value?

• A. 20/200
• B. 20/40
• C. 20/20
• D. 20/60

Answer: (A)

When lighting is low, vision shifts to the rod system, or scotopic vision. Rods are highly sensitive to light but provide poor detail because many rods converge onto the same ganglion cell and because the rods aren’t concentrated in the fovea where cone vision is sharp. That combination lowers spatial resolution, so acuity drops markedly compared with daylight (photopic) vision. In practical terms, night or scotopic acuity is about 20/200, meaning you can discern details at 20 feet that a person with normal vision would need 200 feet to resolve. The other numbers imply better detail resolution than is typical for low-light conditions, so they don’t fit the expected scotopic performance.

When lighting is low, vision shifts to the rod system, or scotopic vision. Rods are highly sensitive to light but provide poor detail because many rods converge onto the same ganglion cell and because the rods aren’t concentrated in the fovea where cone vision is sharp. That combination lowers spatial resolution, so acuity drops markedly compared with daylight (photopic) vision. In practical terms, night or scotopic acuity is about 20/200, meaning you can discern details at 20 feet that a person with normal vision would need 200 feet to resolve. The other numbers imply better detail resolution than is typical for low-light conditions, so they don’t fit the expected scotopic performance.