**Question:** Blue sclera is seen in all of the following conditions except (REPEATED):

A. Pernicious anemia
B. Hypothyroidism
C. Corneal edema
D. Blue-white disc sign (Henle's sign)

**Core Concept:**
Blue sclera refers to the presence of a blue coloration in the sclera (the white part of the eye) due to an increased amount of hemoglobin in the blood vessels. This can be seen in conditions where there is increased hemoglobin or deoxygenated hemoglobin in the blood.

**Why the Correct Answer is Right:**
Hypothyroidism (option B) is characterized by low thyroid hormone levels, which would result in less deoxygenated hemoglobin and thus not causing blue sclera. Pernicious anemia (option A) is a type of anemia characterized by vitamin B12 deficiency leading to ineffective erythropoiesis, resulting in increased deoxygenated hemoglobin and blue sclera. Corneal edema (option C) is a condition characterized by swelling of the cornea, not related to hemoglobin levels or blood oxygenation, and therefore blue sclera will not be seen. The blue-white disc sign (Henle's sign) (option D) is a clinical feature seen in certain neurological conditions like Wernicke-Korsakoff syndrome, where the optic nerve is compressed or damaged. In such cases, there is decreased oxygenation of the optic disc, making it appear blue, but not the sclera.

**Why Each Wrong Option is Incorrect:**
In hypothyroidism, there is a decrease in deoxygenated hemoglobin, which prevents blue sclera. In pernicious anemia, the increased deoxygenated hemoglobin causes blue sclera. Corneal edema is unrelated to hemoglobin levels or blood oxygenation, so blue sclera will not be seen. The blue-white disc sign is a clinical feature related to optic nerve dysfunction, not hemoglobin or oxygenation, so it does not explain blue sclera.

**Clinical Pearl:**
Blue sclera can be an important sign in the differential diagnosis of certain medical conditions. It is essential to differentiate between conditions like pernicious anemia and hypothyroidism based on the presence of blue sclera to guide appropriate diagnostic and therapeutic strategies.