**Core Concept**
Blue sclera refers to the visible appearance of the sclera of the eye, which is normally white, but appears blue or translucent due to the underlying choroid and scleral collagen. This condition can be caused by various factors, including genetic disorders and systemic diseases that affect the structure and composition of the sclera.

**Why the Correct Answer is Right**
Blue sclera is often associated with osteogenesis imperfecta, a genetic disorder that affects the production of collagen, a key component of the sclera. In osteogenesis imperfecta, the sclera appears blue due to the transparency of the collagen fibers, which allows the underlying choroid to be visible. Additionally, conditions such as Marfan syndrome and Ehlers-Danlos syndrome can also cause blue sclera due to abnormalities in collagen production.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because blue sclera can be a feature of osteogenesis imperfecta, a condition that affects collagen production.
**Option B:** Incorrect because Marfan syndrome, a disorder that affects the body's connective tissue, can also cause blue sclera due to collagen abnormalities.
**Option C:** Incorrect because Ehlers-Danlos syndrome, a group of disorders that affect collagen production, can also cause blue sclera.

**Clinical Pearl / High-Yield Fact**
It's essential to note that blue sclera can be a sign of underlying systemic disease, so a thorough medical history and physical examination are necessary to determine the underlying cause.

**Correct Answer: A. Osteopetrosis**