Question

Looking around, I've found a lot of research on the allometry of visual acuity and vision at a distance, but not so much on vision close-up. As I understand it, the near point of vision is largely determined by the optical/focusing power (diopters) of the lens, which is itself determined by the refractive index and lens curvature (lensmaker's equation). Assuming the refractive index is constant, this implies smaller animals should have the more powerful vision (assuming smaller eyes) necessary to resolve something as close to their eyes as their own claws. Does measurement agree with this hypothesis? What is the scaling relationship? Is there a single one, or is it sensitive to eye type like acuity is?

Answer 1

The near point of vision is largely determined by the optical power of the lens. Smaller animals tend to have more powerful vision close-up due to their smaller eyes. The scaling relationship between animal size and lens power may vary depending on eye type and acuity.

Step-by-step explanation:

The near point of vision, which is the shortest distance at which a sharp focus can be obtained, is largely determined by the optical power of the lens. In smaller animals with smaller eyes, the lens has a higher power, allowing them to focus on objects closer to their eyes.

Since the power of the lens is determined by the refractive index and lens curvature, smaller animals with smaller eyes tend to have more powerful vision needed for resolving objects close to their eyes, such as their own claws.

The scaling relationship between the size of the animal and the optical power of its lens may not be a single one, as it could be influenced by the type of eye and other factors like acuity. However, the general trend is that smaller animals have more powerful vision close-up compared to larger animals.