**Core Concept**
Retinal detachment is a condition where the retina separates from the underlying retinal pigment epithelium, leading to vision loss. It can occur due to various factors, including trauma, posterior vitreous detachment, or tumors.

**Why the Correct Answer is Right**
The patient's history of cataract surgery 6 months ago increases the risk of retinal detachment. Posterior vitreous detachment, a common complication of cataract surgery, can lead to retinal tears and subsequent detachment. The patient's sudden loss of vision and presence of floaters are classic symptoms of retinal detachment. The retina's separation from the underlying tissue disrupts the normal transmission of visual signals, resulting in loss of vision.

**Why Each Wrong Option is Incorrect**
**Option A:** Vitreous hemorrhage is a condition where blood accumulates in the vitreous gel, which can cause sudden vision loss. However, it typically presents with a sudden, painless loss of vision, often accompanied by floaters, but it doesn't directly cause retinal detachment.

**Option C:** Central retinal artery occlusion is a condition where the central retinal artery becomes blocked, leading to sudden, painless vision loss. It is often associated with atherosclerosis, hypertension, or vasculitis, and doesn't directly relate to retinal detachment.

**Option D:** Cystoid macular edema is a condition where fluid accumulates in the macula, leading to vision loss. While it can occur after cataract surgery, it typically presents with blurry vision, not sudden loss of vision.

**Clinical Pearl / High-Yield Fact**
Retinal detachment is a medical emergency requiring prompt attention. The "Amsler grid" test can help identify retinal detachment by detecting blind spots and distorted vision. Patients with a history of cataract surgery should be monitored closely for signs of retinal detachment.

**✓ Correct Answer: B. Retinal detachment**