Amplitude of accommodative convergence is:
**Core Concept**
Amplitude of accommodative convergence refers to the maximum amount of convergence (inward rotation) of the eyes that occurs when accommodation (focusing of the eyes) is maximized. This occurs when the ciliary muscles contract, allowing the lens to become more spherical and increasing the refractive power of the eye.
**Why the Correct Answer is Right**
The amplitude of accommodative convergence is directly related to the accommodative response, which is the ability of the eye to focus on objects at different distances. This is mediated by the ciliary muscles, which contract to increase the curvature of the lens. The accommodative response is also influenced by the state of the extraocular muscles, particularly the medial rectus muscle, which rotates the eye inward. The amplitude of accommodative convergence is typically around 10-15 prism diopters (Δ) at a near point of 25 cm.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the amplitude of accommodative convergence is not dependent on the age of the individual. While accommodative ability does decline with age, the amplitude of accommodative convergence remains relatively constant.
**Option B:** This option is incorrect because the amplitude of accommodative convergence is not directly related to the accommodative response at a far point. While the accommodative response is influenced by the state of the eye at a far point, the amplitude of accommodative convergence is specific to the near point.
**Option C:** This option is incorrect because the amplitude of accommodative convergence is not dependent on the refractive error of the individual. While refractive error can affect the accommodative response, the amplitude of accommodative convergence remains relatively constant.
**Clinical Pearl / High-Yield Fact**
The amplitude of accommodative convergence is an important factor in the diagnosis of accommodative esotropia, a type of strabismus that occurs when the eyes turn inward due to excessive accommodative convergence.
**Correct Answer:** C. 15 Δ