**Core Concept**
Kayser-Fleischer ring is a significant clinical finding associated with Wilson's disease, a genetic disorder characterized by excessive accumulation of copper in the body. This condition leads to copper deposition in various tissues, including the cornea and the liver.

**Why the Correct Answer is Right**
The Kayser-Fleischer ring is a brownish-yellow discoloration of the Descemet's membrane in the cornea, resulting from the deposition of copper. This occurs due to the impaired transport of copper from the bloodstream to the liver, leading to its accumulation in the cornea. The presence of Kayser-Fleischer rings is a hallmark of Wilson's disease and can be detected through slit-lamp examination.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Kayser-Fleischer ring is not associated with primary biliary cirrhosis, which is another liver disease but does not involve copper accumulation.
**Option B:** This option is incorrect because primary sclerosing cholangitis, another liver disease, is not typically associated with Kayser-Fleischer ring.
**Option C:** This option is incorrect because hemochromatosis, a genetic disorder of iron metabolism, does not involve copper accumulation.

**Clinical Pearl / High-Yield Fact**
Kayser-Fleischer rings can also be seen in other conditions involving copper accumulation, such as Indian childhood cirrhosis and chronic cholestasis. However, Wilson's disease remains the most common cause of Kayser-Fleischer rings.

**Correct Answer: D. Wilson's disease.**