**Core Concept**
Prominent corneal nerves are a characteristic feature in several genetic disorders and systemic diseases that affect the cornea. These nerves are typically absent or reduced in normal individuals and are often associated with corneal diseases or conditions.

**Why the Correct Answer is Right**
Macular dystrophy is a rare genetic disorder that affects the macula, the part of the retina responsible for central vision. Unlike the other options listed, macular dystrophy does not typically present with prominent corneal nerves. In fact, the cornea is usually unaffected in macular dystrophy, making this the correct answer. The prominent corneal nerves are more commonly associated with conditions that directly affect the cornea, such as ectodermal dysplasia, ichthyosis, and Refsum's syndrome.

**Why Each Wrong Option is Incorrect**
**Option A:** Ectodermal dysplasia is a group of disorders that affect the ectodermal layer of the skin and its appendages, including the cornea. In some cases, ectodermal dysplasia can present with prominent corneal nerves, making it an incorrect choice.

**Option B:** Ichthyosis is a group of skin disorders characterized by dry, scaly skin. Some forms of ichthyosis can affect the eyes, including the cornea, and may present with prominent corneal nerves.

**Option C:** Refsum's syndrome is a rare genetic disorder that affects the metabolism of phytanic acid, leading to a range of systemic symptoms including prominent corneal nerves. This makes Refsum's syndrome an incorrect choice.

**Clinical Pearl / High-Yield Fact**
When examining a patient with a suspected corneal disease, it's essential to note the presence or absence of prominent corneal nerves, as this can provide valuable information about the underlying condition.

**✓ Correct Answer: D. Macular dystrophy**