**Question:** A young man with blurring of vision in right eye, followed by left eye after 3 months, showing disc hyperemia, edema, circumpapillary telangiectasia with normal pupillary response and centrocecal scotoma on perimetry, the cause is

A. Diabetes mellitus
B. Hypertension
C. Glaucoma
D. Cataract

**Core Concept:**

The clinical presentation described involves a combination of ocular symptoms and findings, including visual disturbances, optic disc changes, and a specific pattern of visual field defect. This case is relevant to understanding various ocular pathologies and their diagnostic criteria.

**Why the Correct Answer is Right:**

The correct answer is **C. Glaucoma**, as it presents with characteristic optic nerve head changes (hyperemia, edema, and telangiectasia) and a specific visual field defect (centrocecal scotoma). Glaucoma is a group of diseases characterized by optic nerve damage, leading to a progressive loss of vision, particularly in the peripheral visual field. Although some risk factors like diabetes and hypertension can contribute to optic nerve damage, the specific presentation in this question points more towards glaucoma.

**Why Each Wrong Option is Incorrect:**

**A. Diabetes mellitus:** While diabetes can cause retinopathy, it primarily affects the retinal vessels and does not typically present with the described optic nerve head changes and visual field defect. Diabetes can cause optic nerve damage, but the specific pattern of disc changes and visual field defect suggest glaucoma as the primary diagnosis.

**B. Hypertension:** Hypertension can lead to optic nerve damage, but the specific pattern of disc changes and visual field defect are more consistent with glaucoma. Additionally, hypertension usually presents with retinopathy, not optic disc changes.

**D. Cataract:** Cataract is a condition affecting the lens, causing vision impairment and often inducing a characteristic "ring of Krukenberg" on fundoscopy. The described optic nerve head changes and visual field defect are more consistent with glaucoma.

**Clinical Pearl:**

The clinical pearl from this question is to be aware of the characteristic optic nerve head changes and visual field defect in glaucoma and differentiate them from other conditions like diabetes and hypertension, which typically present with different fundoscopic findings and visual field defects. Early diagnosis and management of glaucoma are crucial to prevent irreversible vision loss.