**Core Concept**
Presbyopia is a age-related decline in the ability to focus on close objects, typically starting in the early to mid-40s. It is caused by a decrease in the elasticity of the lens and a reduction in the ciliary muscle's ability to focus the lens for near vision.

**Why the Correct Answer is Right**
The rapid change of presbyopic glasses is often due to the natural progression of presbyopia, which can cause a significant change in the patient's refractive error over a short period. This is because the lens becomes stiffer and less able to accommodate for near vision, leading to a greater need for correction. The rate of change can vary between individuals, but it is generally most rapid in the early stages of presbyopia.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because presbyopia is not caused by a change in the shape of the eye, but rather a decrease in the lens's ability to focus for near vision.
**Option B:** This option is incorrect because hyperopia (farsightedness) is a separate condition from presbyopia, although the two can coexist.
**Option C:** This option is incorrect because myopia (nearsightedness) is a separate condition from presbyopia, although the two can coexist.

**Clinical Pearl / High-Yield Fact**
The change in presbyopic glasses is often most rapid in the early stages of presbyopia, typically between the ages of 40-45. It's essential to monitor patients' refractive errors closely during this period to ensure accurate correction and optimal vision.

**Correct Answer: C. Myopia**