**Complicated Cataract Core Concept**
Complicated cataract, also known as complicated cataract of trauma or secondary cataract, refers to a cataract that develops as a result of an underlying ocular or systemic condition. In this context, the lens becomes opacified due to a pathologic process, often secondary to trauma, uveitis, or retinal detachment.

**Why the Correct Answer is Right**
The development of complicated cataract is often linked to the release of inflammatory mediators and the subsequent formation of posterior subcapsular cataract (PSC). This process involves the activation of various cellular pathways, including the complement system, which contributes to the opacification of the lens. The exact mechanism remains unclear, but it is believed to involve the breakdown of the blood-ocular barrier, allowing inflammatory cells and mediators to penetrate the lens capsule.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because age-related cataract is a distinct entity, characterized by the gradual accumulation of protein aggregates in the lens, leading to opacification.
**Option B:** This option is incorrect because posterior segment diseases such as retinal detachment, while associated with complicated cataract, do not directly cause cataract formation.
**Option C:** This option is incorrect because systemic conditions such as diabetes mellitus can cause cataract formation, but they are not the primary cause of complicated cataract.

**Clinical Pearl / High-Yield Fact**
It is essential to differentiate complicated cataract from age-related cataract, as the former often requires prompt intervention to prevent further vision loss.

**Correct Answer: B. Posterior segment diseases**