**Question:** Keratometry is useful in measuring

A. curvature of the cornea
B. intraocular pressure
C. lens power
D. retinal thickness

**Core Concept:**

Keratometry is a clinical test used to measure the curvature of the cornea, which is a key component of assessing the overall health and refractive error of the eye. The cornea is the outermost part of the cornea and plays a crucial role in focusing light onto the retina, facilitating clear vision.

**Why the Correct Answer is Right:**

Keratometry measures the curvature of the cornea using a special instrument called a keratometer or keratometer, which is essential in understanding the refractive power of the cornea. This information is crucial for ophthalmologists to diagnose various eye conditions, such as keratoconus, astigmatism, and irregular astigmatism, and determine the appropriate treatment options, such as spectacles or contact lenses.

**Why Each Wrong Option is Incorrect:**

1. Keratometry is not used to measure the curvature of the lens, which is responsible for focusing light onto the retina, unlike the cornea. Therefore, option C (lens power) is incorrect.
2. Keratometry does not assess the intraocular pressure (option B), which is determined using devices like tonometers or applanation tonometers.
3. Retinal thickness (option D) is typically measured using optical coherence tomography (OCT) or ultrasound biometry, not keratometry.

**Clinical Pearl:**

Understanding the principles of keratometry helps medical professionals diagnose and manage various ocular conditions accurately, ensuring appropriate treatment and optimal visual outcomes for patients.