**Core Concept**
The refractive power of the eye is determined by the combination of refractive indices and distances between the cornea, lens, and retina. The eye's ability to focus light is a critical aspect of vision.

**Why the Correct Answer is Right**
The correct answer is **e) Axial length of the eye**. The axial length of the eye, which is the distance from the cornea to the retina, plays a crucial role in determining the refractive power of the eye. This is because the axial length affects the focal length of the eye, with a longer axial length resulting in a shorter focal length and increased refractive power. The axial length is influenced by the curvature of the cornea and the shape of the lens, making it a critical factor in determining the eye's refractive power.

**Why Each Wrong Option is Incorrect**
* **Option A:** The lens does contribute to the eye's refractive power, but it is not the main factor. The lens' refractive power is adjustable, and it can change shape to focus on objects at different distances.
* **Option B:** The cornea is indeed a major contributor to the eye's refractive power, but it is not the only factor. The cornea's refractive power is fixed and depends on its curvature.
* **Option C:** Vitreous hemorrhage can affect vision by blocking light and causing bleeding in the eye, but it does not directly affect the eye's refractive power.
* **Option D:** Aqueous humor is the clear fluid in the eye that nourishes the cornea and lens, but it does not play a significant role in determining the eye's refractive power.

**Clinical Pearl / High-Yield Fact**
The axial length of the eye is a critical factor in determining refractive errors, such as myopia (nearsightedness) and hyperopia (farsightedness). This is why axial length is often measured during eye exams to diagnose and correct refractive errors.

**Correct Answer:** E. Axial length of the eye