**Core Concept**
The convergence of light rays on the retina is a critical aspect of vision, and it is primarily facilitated by the refractive power of the eye. The most important factor determining this convergence is the curvature of the cornea and lens, which refracts light rays and focuses them onto the retina.

**Why the Correct Answer is Right**
The correct answer is **C. Refractive power of the lens and cornea**. The refractive power of the cornea and lens is responsible for bending light rays and converging them onto the retina. The cornea, being the most powerful refracting surface, accounts for approximately 2/3 of the eye's total refractive power, while the lens contributes the remaining 1/3. The combination of these refractive powers ensures that light rays are focused precisely onto the retina, enabling us to perceive clear and distinct images.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the pupil size does not significantly affect the convergence of light rays on the retina. While the pupil does regulate the amount of light entering the eye, its size does not influence the focal point of light rays.

**Option B:** This option is incorrect because the vitreous humor, although a clear gel-like substance, does not play a significant role in refracting light rays. Its primary function is to maintain the eye's shape and provide nutrients to the retina.

**Option D:** This option is incorrect because the retina itself is not responsible for refracting light rays. Instead, it is the light-sensitive tissue that converts visual information into electrical signals transmitted to the brain.

**Clinical Pearl / High-Yield Fact**
A significant factor in the development of myopia (nearsightedness) is the elongation of the eye, which affects the refractive power of the cornea and lens. This can lead to a decrease in the eye's ability to converge light rays onto the retina, resulting in blurred vision at a distance.

**Correct Answer:** C. Refractive power of the lens and cornea