**Core Concept**
Esotropia, also known as convergent strabismus, is a type of strabismus characterized by a turning inward of one or both eyes. This condition can be caused by various factors, including refractive errors that lead to unequal vision between the two eyes.

**Why the Correct Answer is Right**
Esotropia is commonly associated with hypermetropia (farsightedness), as the brain attempts to compensate for the lack of near vision by turning the eye inward. This is because the farsighted eye is unable to converge properly, leading to a misalignment of the eyes. The increased accommodative effort required to see near objects can cause the farsighted eye to turn inward, resulting in esotropia. The convergence of the farsighted eye can be influenced by the parasympathetic innervation of the ciliary muscle and the resulting increase in lens curvature.

**Why Each Wrong Option is Incorrect**
**Option A:** Myopia (nearsightedness) is not commonly associated with esotropia, as the nearsighted eye tends to diverge rather than converge.
**Option B:** Astigmatism is a type of refractive error that affects the curvature of the cornea or lens, but it is not typically associated with esotropia.
**Option C:** Presbyopia is a age-related condition that affects the ability to focus on near objects, but it is not a common cause of esotropia.

**Clinical Pearl / High-Yield Fact**
In children, esotropia can often be a sign of underlying hypermetropia, and correction of the hypermetropia can lead to improvement or resolution of the esotropia.

**Correct Answer: C. Hypermetropia. Hypermetropia is commonly associated with esotropia, as the brain attempts to compensate for the lack of near vision by turning the eye inward.**