**Core Concept**
Hypermetropia, also known as farsightedness, is a condition where distant objects are seen clearly, but nearby objects appear blurry. It occurs when the eyeball is too short, the cornea is too flat, or the lens is too thin, resulting in an inability to focus light properly on the retina.

**Why the Correct Answer is Right**
Anterior dislocation of the lens, also known as subluxation, typically results in myopia (nearsightedness) due to the increased power of the lens. This is because the lens is displaced forward, causing it to become more powerful and focusing light in front of the retina, making distant objects appear blurry. The increased refractive index of the cortex of the lens (Option C) can contribute to hypermetropia by increasing the focusing power of the lens. A short axial length of the eyeball (Option A) and a flat cornea (Option B) are both causes of hypermetropia, as they reduce the overall power of the eye.

**Why Each Wrong Option is Incorrect**
**Option A:** A short axial length of the eyeball is a common cause of hypermetropia, as it reduces the overall power of the eye.
**Option B:** A flat cornea is also a cause of hypermetropia, as it reduces the refractive power of the cornea.
**Option C:** An increased refractive index of the cortex of the lens can contribute to hypermetropia by increasing the focusing power of the lens.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that hypermetropia can be caused by a combination of factors, including a short axial length of the eyeball, a flat cornea, or an increased refractive index of the lens cortex. Anterior dislocation of the lens typically results in myopia, not hypermetropia.

**✓ Correct Answer: D. Anterior dislocation of the lens**