**Core Concept**
Sunflower cataract is a type of posterior subcapsular cataract characterized by a petaloid or sunflower-like appearance. This condition is associated with posterior capsule opacification, which can be caused by various factors, including aging, trauma, and exposure to radiation or certain medications.

**Why the Correct Answer is Right**
Sunflower cataract is typically seen in patients with diabetes mellitus, as the high glucose levels can cause osmotic changes leading to water influx into the lens, resulting in swelling and opacification of the lens fibers. This condition is often bilateral and can be associated with other complications of diabetes, such as retinopathy and nephropathy. The posterior subcapsular region of the lens is particularly susceptible to damage due to its high metabolic rate and presence of the visual axis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while aging is a common cause of cataract, it does not typically result in a sunflower cataract.
**Option B:** This option is incorrect because while trauma can cause cataract, it is not the most common cause of sunflower cataract.
**Option C:** This option is incorrect because while radiation can cause cataract, it is not the most common cause of sunflower cataract.

**Clinical Pearl / High-Yield Fact**
Sunflower cataract is a type of cataract that can be associated with other complications of diabetes, such as retinopathy and nephropathy. It is essential to monitor patients with diabetes for signs of cataract and refer them to an ophthalmologist for timely evaluation and treatment.

**Correct Answer: D. Diabetes mellitus.**