**Core Concept:** Cataracts are a common opacity or clouding of the crystalline lens in the eye, which can impair vision. They are classified into four types based on their morphology: nuclear, cortical, subcapsular, and posterior subcapsular.

**Why the Correct Answer is Right:** The most visually handicapping type of cataract is the **posterior subcapsular cataract**. This type of cataract occurs near the back of the lens, affecting the lens's ability to focus light properly on the retina. It is often associated with aging, diabetes, or long-term use of corticosteroids.

**Why Each Wrong Option is Incorrect:**

A. **Nuclear cataract:** While nuclear cataracts are common, they are less visually handicapping compared to posterior subcapsular cataracts, as they primarily affect the lens's ability to transmit light and scatter it, rather than focusing it.

B. **Cortical cataract:** Although cortical cataracts form in a spiral pattern around the equator of the lens, they are less visually handicapping than posterior subcapsular cataracts, as they primarily affect the lens's ability to transmit light, rather than focusing it.

C. **Capsular cataract:** Although capsular cataracts occur in the capsule surrounding the lens, they are less visually handicapping than posterior subcapsular cataracts, as they primarily affect the lens's ability to transmit light, rather than focusing it.

**Clinical Pearl:** Posterior subcapsular cataracts are often associated with diabetes, steroid use, or other systemic conditions that cause increased lens protein denaturation and aggregation, leading to a significant reduction in light focusing ability.

**Answer Explanation:** The correct answer is **D**. Posterior subcapsular cataracts are the most visually handicapping type due to their location near the lens's back surface, affecting the focusing of light on the retina, leading to visual impairment.