## Core Concept
A nuclear cataract is a type of age-related cataract that affects the central part of the lens, known as the nucleus. It is characterized by hardening and yellowing of the lens nucleus, leading to changes in vision. This condition can cause various visual disturbances.

## Why the Correct Answer is Right
The correct answer, myopia (nearsightedness), can occur in nuclear cataracts due to the increased refractive index of the lens nucleus as it ages and becomes more compact. This change can cause the lens to become more curved, leading to a shift towards myopia. Patients might notice an improvement in near vision, a phenomenon sometimes referred to as "second sight," before the cataract significantly impairs vision.

## Why Each Wrong Option is Incorrect
* **Option A:** Hyperopia (farsightedness) is typically associated with conditions where the eyeball is too short or the lens is not sufficiently curved, which is the opposite of what occurs in nuclear cataracts.
* **Option C:** Astigmatism refers to a condition where the cornea or lens isn't perfectly round, causing blurred vision at all distances. While cataracts can cause astigmatism, it's not the most directly related effect of nuclear cataracts compared to myopia.
* **Option D:** Presbyopia is age-related loss of near vision that occurs due to decreased elasticity of the lens, distinct from the refractive changes caused by nuclear cataracts.

## Clinical Pearl / High-Yield Fact
A key point to remember is that nuclear cataracts can cause a temporary improvement in near vision (a "second sight" phenomenon) due to the increased curvature of the lens, which can lead to myopia. This is a classic clinical correlation that can help in diagnosing and understanding the progression of nuclear cataracts.

## Correct Answer Line
**Correct Answer: B. Myopia**