**Core Concept**
Eale's disease is a rare, idiopathic inflammatory disorder affecting the retinal and choroidal vessels, often presenting with sudden, painless loss of vision in young adults.

**Why the Correct Answer is Right**
Eale's disease typically affects individuals between 20 and 40 years of age, with a higher incidence in males. The disease is characterized by recurrent retinal and vitreal hemorrhages, often accompanied by retinal neovascularization. The exact cause of Eale's disease remains unknown, but it is believed to result from an abnormal immune response, leading to inflammation and damage to the retinal vessels. In this case, the patient's painless sudden loss of vision, in conjunction with an unremarkable ocular and systemic examination, makes Eale's disease a likely diagnosis.

**Why Each Wrong Option is Incorrect**

**Option A:** Retinal detachment is a condition where the retina separates from the underlying retinal pigment epithelium, often presenting with sudden visual loss, but typically accompanied by symptoms such as flashing lights, floaters, and eye pain.

**Option C:** Glaucoma is a group of eye conditions that damage the optic nerve, often resulting from increased intraocular pressure. While glaucoma can cause sudden loss of vision, it is typically accompanied by eye pain, redness, and blurred vision.

**Option D:** Cataract is a clouding of the lens in the eye, leading to vision impairment. Cataracts are often age-related and may present with gradual vision loss, but are typically not associated with sudden painless loss of vision.

**Clinical Pearl / High-Yield Fact**
Eale's disease is often referred to as "idiopathic retinal vasculitis," emphasizing the unknown etiology of the disease and the role of inflammation in its pathogenesis.

**Correct Answer:**
✓ Correct Answer: B. Eale's disease