**Core Concept**
Diabetes mellitus can cause cataracts due to the non-enzymatic glycation of lens proteins, leading to the formation of advanced glycosylation end-products (AGEs). This process alters the structure and function of the lens proteins, resulting in cataract formation.

**Why the Correct Answer is Right**
Glycation of lens proteins, specifically crystallins, occurs when glucose molecules bind to amino groups on the proteins, leading to the formation of glycated crystallins. This process is accelerated in diabetes mellitus due to the high blood glucose levels. The glycated crystallins accumulate in the lens, causing opacification and cataract formation. The correct answer, glycated crystallins, highlights the key role of glycation in cataract development in diabetes.

**Why Each Wrong Option is Incorrect**
**Option B:** Calcified crystallins are not directly related to diabetes mellitus-induced cataracts. While calcification can occur in the lens, it is not the primary mechanism in diabetic cataracts.
**Option C:** Fibrillins are proteins found in connective tissue, not in the lens. Glycation of fibrillins is not relevant to cataract formation in diabetes.
**Option D:** Calcified fibrillins are again not relevant to diabetic cataracts, and fibrillins are not typically associated with the lens.

**Clinical Pearl / High-Yield Fact**
Remember that diabetic cataracts are typically posterior subcapsular cataracts (PSCs), which can be a presenting feature of diabetes mellitus. Early detection and management of diabetes are crucial to prevent cataract formation.

**✓ Correct Answer:** A. Glycated crystallins