**Core Concept**
The keratometer is an ophthalmic instrument used to measure the curvature of the cornea, a critical parameter in assessing refractive errors and planning for refractive surgery.

**Why the Correct Answer is Right**
The keratometer works by projecting a mire (a pattern of concentric rings) onto the cornea and measuring the angle of reflection. This angle is related to the radius of curvature of the cornea. The keratometer's measurements are essential for calculating the power of the cornea, which is crucial in determining the patient's refractive error and planning for refractive surgeries like LASIK. The keratometer's accuracy is critical in ensuring that the patient's vision is corrected accurately.

**Why Each Wrong Option is Incorrect**
**Option A:** The keratometer is not used to measure the curvature of the crystalline lens.
The keratometer is specifically designed to measure the curvature of the cornea, not the crystalline lens.

**Option B:** The keratometer is not used to assess the intraocular pressure.
The intraocular pressure is typically measured using a tonometer, not a keratometer.

**Option C:** The keratometer is not used to measure the depth of the anterior chamber.
The depth of the anterior chamber is typically measured using an ultrasonography or a slit-lamp biomicroscope, not a keratometer.

**Clinical Pearl / High-Yield Fact**
Remember the mnemonic "Keratometer Kicks Off Refractive Surgery" to recall the keratometer's role in planning for refractive surgery.

**Correct Answer: C. Corneal curvature.**