**Core Concept**
Band keratopathy is a type of corneal calcification that occurs due to the deposition of calcium salts in the corneal stroma, leading to opacification and visual impairment. This condition is often associated with systemic diseases, such as hyperparathyroidism, sarcoidosis, and chronic kidney disease.

**Why the Correct Answer is Right**
Calcium deposits in band keratopathy are primarily composed of calcium phosphate, which is deposited in the corneal stroma due to an imbalance in the calcium-phosphate equilibrium. This can occur in conditions where there is an excess of calcium in the blood, such as hyperparathyroidism, or in conditions where there is a decrease in the clearance of calcium, such as chronic kidney disease. The deposition of calcium phosphate leads to the formation of a band-like opacity in the cornea.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while calcium carbonate is a type of calcium salt, it is not the primary component deposited in band keratopathy.
**Option B:** This option is incorrect because calcium oxalate is more commonly associated with calcium oxalate kidney stones, not band keratopathy.
**Option C:** This option is incorrect because while calcium hydroxide is used in some medical applications, it is not the primary component deposited in band keratopathy.

**Clinical Pearl / High-Yield Fact**
Band keratopathy is often associated with systemic diseases, and a thorough investigation for underlying conditions is essential in the management of this condition. Mnemonic: "CASH" - Calcium, Alkalinity, Sarcoidosis, and Hyperparathyroidism are common causes of band keratopathy.

**Correct Answer:** C. Calcium phosphate.