What is the refractive error characterized by difficulty focusing on nearby objects?

The refractive error characterized by difficulty focusing on nearby objects is presbyopia. This condition typically occurs as a result of aging, where the eye's lens becomes less flexible over time, making it challenging to focus on close-up tasks such as reading or knitting. Unlike other refractive errors, presbyopia is not caused by an inherent shape of the eyeball but rather the natural aging process that affects the elasticity of the lens.

In contrast, myopia, or nearsightedness, involves difficulty seeing distant objects clearly, while close-up vision is usually unaffected. Astigmatism is due to an irregular curvature of the cornea or lens, leading to blurred vision at all distances. Hyperopia, or farsightedness, causes trouble focusing on nearby objects but differs from presbyopia, as it can occur at any age and is often associated with the eyeball's shape rather than the aging of the lens. Therefore, presbyopia is the most accurate term for the condition described, as it specifically refers to the age-related decline in near vision.