**Core Concept**
The equatorial diameter of the lens is a critical anatomical parameter in ophthalmology, referring to the widest dimension of the lens across its equatorial plane. This dimension is essential in understanding lens anatomy, particularly in conditions affecting lens shape and size, such as cataracts.

**Why the Correct Answer is Right**
The equatorial diameter of the lens is approximately 10-11 mm in adults, which is crucial for surgical planning and lens implantation. This dimension is determined by the lens capsule, which is a transparent, elastic structure that encloses the lens. The equatorial diameter is also influenced by the zonular fibers, which are delicate, elastic fibers that attach the lens to the ciliary body.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not within the normal range of equatorial diameters.
**Option B:** This option is incorrect because it is not a commonly referenced value for equatorial diameter in ophthalmology.
**Option C:** This option is incorrect because it is not the correct value for equatorial diameter.

**Clinical Pearl / High-Yield Fact**
In ophthalmic surgery, knowledge of the equatorial diameter is essential for accurate lens implantation, particularly in cases of cataract surgery.

**Correct Answer:** C. 11 mm