## Core Concept
The question tests the understanding of how changes in the refractive medium of the eye affect vision. When water enters the eyes, it alters the refractive index of the cornea and the anterior chamber, impacting the eye's ability to focus light properly.

## Why the Correct Answer is Right
The correct answer, , involves the change in the refractive index of the cornea when it comes into contact with water. The cornea has a specific refractive index that contributes significantly to the eye's total optical power. When water enters the eye, it changes the cornea's surface refractive index, leading to a change in the way light is bent (refracted) as it enters the eye. This change disrupts the precise focusing of light on the retina, causing blurring of vision. The cornea's surface is normally protected by a tear film, and any alteration, such as the introduction of water, can temporarily affect vision.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because the primary issue with water in the eyes is not related to the lens's ability to change shape for focusing on near objects.
- **Option B:** This option is incorrect because, although the retina does convert light into signals sent to the brain, the immediate blurring of vision upon water entering the eyes is not due to a problem with the retina itself but rather with the refractive media.
- **Option C:** This option might seem plausible because it involves a part of the eye, but it is not directly relevant to the immediate effect of water on vision.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the cornea is responsible for a significant portion of the eye's total optical power, and any change in its surface properties, such as with water entry, can cause immediate vision disturbances. Clinically, this is why procedures like cataract surgery are done carefully to maintain the integrity of the cornea and why eye wash stations are used with caution.

**Correct Answer: D.**