**Core Concept**
The question requires knowledge of the different types of cataracts and their impact on vision. Cataracts are classified based on their location and morphology, which can affect the severity of visual impairment.

**Why the Correct Answer is Right**
Posterior subcapsular cataracts (PSC) are a type of age-related cataract that affects the posterior part of the lens capsule. They are characterized by a small, opaque area that can grow and spread, causing significant visual disturbance. PSC cataracts are particularly handicapping because they can cause glare, halos, and significant reduction in visual acuity, especially in low-light conditions. This is due to the location of the opacity, which is closest to the retina and affects the visual pathway.

**Why Each Wrong Option is Incorrect**
**Option A:** Cortical cataracts, also known as cortical sclerosis, are characterized by white, wedge-shaped opacities that start in the periphery of the lens and work their way towards the center. While they can cause significant visual impairment, they are typically less handicapping than PSC cataracts.

**Option B:** Nuclear cataracts involve the central part of the lens and cause progressive hardening and yellowing of the lens nucleus. They can cause significant visual impairment, but the impact is often more gradual and less handicapping than PSC cataracts.

**Option D:** Zonular cataracts, also known as lamellar cataracts, are characterized by opacities that occur in specific zones or layers of the lens. While they can cause significant visual impairment, they are typically less handicapping than PSC cataracts.

**Clinical Pearl / High-Yield Fact**
It's essential to recognize that PSC cataracts can be a sign of underlying systemic conditions, such as diabetes or corticosteroid use, and may require prompt evaluation and treatment to prevent further visual decline.

**✓ Correct Answer: C. Posterior subcapsular**