**Core Concept:** Presbyopia is a natural age-related loss of the eye's ability to focus on near objects, which occurs in middle-aged adults.

**Why the Correct Answer is Right:** Presbyopia is a common eye condition that affects individuals as they age. It is characterized by a decrease in the eye's ability to focus on near objects, a process that occurs gradually over time. In this case, the patient's decreased distance vision and the fact that he no longer needs his near glasses for near work indicates that he is likely experiencing presbyopia.

**Why Each Wrong Option is Incorrect:**

A. **Nearsightedness (Myopia)**: Nearsightedness is a condition where distant objects appear blurry, while near objects are clear. In this scenario, the patient's decreased distance vision is consistent with nearsightedness, but the fact that he no longer needs his near glasses rules out this option.

B. **Farsightedness (Hyperopia)**: Farsightedness is a condition where near objects appear blurry, while distant objects are clear. Similar to nearsightedness, this option is consistent with the patient's decreased distance vision, but the lack of change in near vision disqualifies it as the correct answer.

C. **Cataract**: A cataract is a clouding of the lens within the eye, which can lead to vision impairment and change in prescription needs. However, the patient's unchanged near vision makes this option less likely.

D. **Astigmatism**: Astigmatism is a refractive error where distant objects are not clearly focused due to an irregular corneal curvature. While astigmatism can contribute to decreased distance vision, the patient's unchanged near vision eliminates it as the primary cause.

**Clinical Pearl:** The differentiation between nearsightedness, farsightedness, presbyopia, and cataract is essential for understanding different causes of decreased vision in adults. In presbyopia, the vision for both distance and near tasks deteriorates simultaneously. In contrast, other causes typically affect distance vision more than near vision.