## **Core Concept**
The power of an intraocular lens (IOL) is determined by its ability to refract light and focus it properly on the retina. This is crucial for restoring vision in patients who have undergone cataract surgery. The power of the IOL is measured in diopters (D) and is calculated based on the curvature of the lens and the refractive indices of the lens material and the surrounding media.

## **Why the Correct Answer is Right**
The correct answer, **B. Refractive index and curvature of the lens**, is right because the power of an IOL is primarily determined by its refractive index and the curvature of its surfaces. The lens maker's formula, which is used to calculate the power of the IOL, takes into account the refractive indices of the IOL material and the surrounding media (such as the aqueous and vitreous humors), as well as the curvature of the anterior and posterior surfaces of the lens. A higher refractive index or a steeper curvature results in a higher power IOL.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because, while the power of an IOL does affect the **refractive status** of the eye, it is not directly determined by the refractive status of the eye. Instead, the IOL power is chosen to correct the refractive error caused by the removal of the cataractous lens.
- **Option C:** This option is incorrect because the **size of the IOL** can affect the overall fit and stability of the lens within the capsular bag but does not directly determine its power. The size of the IOL is more related to the physical dimensions and the material's properties rather than its optical power.
- **Option D:** This option is incorrect because **the type of IOL material** (e.g., PMMA, acrylic, silicone) can affect the biocompatibility, flexibility, and optical properties of the IOL but does not solely determine its power. Different materials may have different refractive indices, which can influence the IOL's power, but the material type is not the direct determinant.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the power of an IOL is calculated using the **SRK (Sanders-Retzlaff-Kraft) formula** or other similar formulas, which take into account the axial length of the eye and the curvature of the cornea, in addition to the desired postoperative refractive error. Accurate calculation of IOL power is critical for achieving optimal visual outcomes after cataract surgery.

## **Correct Answer:** B. Refractive index and curvature of the lens.