**Core Concept**
Keratoconus is a progressive eye disease characterized by thinning and conical protrusion of the cornea, leading to impaired vision. It is a complex condition involving both genetic and environmental factors.

**Why the Correct Answer is Right**
Keratoconus typically manifests in adolescence or early adulthood, not immediately after birth. The exact cause of keratoconus is not known, but it is believed to result from a combination of genetic and environmental factors, such as eye rubbing, which can cause mechanical stress on the cornea. Keratoconus is not a congenital condition and does not usually present with symptoms in infancy.

**Why Each Wrong Option is Incorrect**
**Option A:** Keratoconus can indeed be associated with Down's syndrome, as well as other genetic disorders, such as Ehlers-Danlos syndrome. Individuals with these conditions are at increased risk of developing keratoconus.
**Option C:** The Munson sign, also known as Fleischer ring or Munson's sign, is a characteristic clinical finding in keratoconus. It refers to a ring of iron deposition in the cornea, visible on slit-lamp examination.
**Option D:** In severe cases of keratoconus, corneal transplantation may be necessary to restore vision. This is often considered when the cornea has become significantly thin or irregular, and other treatments have failed to improve vision.

**Clinical Pearl / High-Yield Fact**
Keratoconus is often associated with a history of eye rubbing, which can exacerbate the condition. Educating patients about the importance of avoiding eye rubbing and using proper eye care techniques can help slow the progression of keratoconus.

**✓ Correct Answer: B. It manifests just after bih**