**Core Concept**
A non-healing corneal ulcer is a complication that can arise from various factors, ultimately leading to corneal damage and vision loss. It is essential to identify the underlying causes to initiate appropriate treatment and prevent further complications. The causes of non-healing corneal ulcers include infection, trauma, and systemic conditions.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of corneal ulcers. A non-healing corneal ulcer can be caused by persistent bacterial or fungal infections, which can lead to the release of toxins and the destruction of corneal tissue. Additionally, systemic conditions such as diabetes mellitus, rheumatoid arthritis, and vitamin A deficiency can impair corneal healing. The presence of a foreign body, such as a contact lens, can also cause a non-healing corneal ulcer.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not a known cause of non-healing corneal ulcers.
* **Option B:** This option is not a recognized cause of non-healing corneal ulcers.
* **Option C:** This option is not a valid choice, as it is not a cause of non-healing corneal ulcers.

**Clinical Pearl / High-Yield Fact**
A non-healing corneal ulcer can be a sign of a systemic infection or autoimmune disease, and prompt investigation and treatment are necessary to prevent vision loss and other complications.

**Correct Answer:** D.