**Core Concept**
Complicated cataract refers to a type of cataract that develops as a result of intraocular inflammation, trauma, or other ocular conditions. This type of cataract is characterized by the formation of posterior subcapsular cataracts, cortical cataracts, or mixed cataracts.

**Why the Correct Answer is Right**
Complicated cataracts are a result of the release of inflammatory mediators and cytokines within the eye, leading to the denaturation of lens proteins and the formation of cataractous opacities. The inflammation can cause damage to the lens epithelium, leading to the formation of posterior subcapsular cataracts. Additionally, the inflammation can also cause the precipitation of proteinaceous material within the lens cortex, leading to the formation of cortical cataracts.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not specify a condition that leads to the development of complicated cataract.
**Option B:** This option is incorrect as it refers to a type of cataract that develops due to aging or other non-inflammatory conditions.
**Option C:** This option is incorrect as it refers to a type of cataract that develops due to metabolic disorders or systemic diseases.

**Clinical Pearl / High-Yield Fact**
In complicated cataract, the posterior subcapsular cataract is often the first sign of cataract formation, and it can progress rapidly to cause significant visual impairment. Early recognition and management of the underlying condition are crucial to prevent the progression of cataract.

**Correct Answer: D. Complicated cataract in diabetes is an example of a complicated cataract that develops due to systemic disease.**