A 58-year-old man with a 10-year history of primary open-angle glaucoma presents for routine fundoscopy. Examination reveals the structure marked **A** in the diagram — an increased cup-to-disc ratio of 0.75 with vertical elongation. The patient reports no ocular pain and denies any recent vision loss. Gonioscopy confirms an open angle. Which of the following best explains the pathophysiology underlying this optic disc finding?

Explanation

## Why "Mechanical compression and ischemic injury at the lamina cribrosa leading to retrograde axonal degeneration of retinal ganglion cells" is right The structure marked **A** — an increased cup-to-disc ratio (>0.7) with vertical elongation — is the hallmark of glaucomatous optic neuropathy. The pathogenesis is well-established: elevated intraocular pressure (or pressure-independent mechanisms in normal-tension glaucoma) causes mechanical compression and ischemic injury at the lamina cribrosa, the site of maximum axonal vulnerability. This leads to retrograde axonal degeneration of retinal ganglion cells, progressive thinning of the neuroretinal rim (especially following the ISNT rule: Inferior > Superior > Nasal > Temporal), and deepening/widening of the optic cup. This is the direct mechanism linking IOP elevation to the characteristic disc cupping seen in the diagram (Yanoff 5e Ch 10.10; Kanski 9e Ch 11). ## Why each distractor is wrong - **Direct inflammatory infiltration of the optic nerve head causing demyelination**: This describes optic neuritis or inflammatory optic neuropathy (e.g., in multiple sclerosis), not glaucomatous neuropathy. Glaucoma is a mechanical/ischemic process, not primarily inflammatory. The disc appearance and visual field defects differ significantly. - **Acute vascular occlusion of the posterior ciliary arteries**: This would cause acute, painful vision loss and sudden disc swelling or pallor, not the insidious, painless, progressive cupping seen in this patient's 10-year history. Glaucomatous cupping develops gradually over years. - **Congenital hypoplasia of the optic nerve**: Congenital optic nerve hypoplasia presents from birth or early childhood with a small, pale disc and does not progress in the manner described. The patient's 10-year history of glaucoma with documented progression rules out a static congenital anomaly. **High-Yield:** Glaucomatous optic neuropathy = mechanical compression + ischemia at lamina cribrosa → retrograde RGC axonal loss → progressive cupping (C/D >0.7, vertical elongation) + ISNT rim thinning + visual field defects (arcuate/Bjerrum scotoma). [cite: Yanoff Ophthalmology 5e Ch 10.10; Kanski 9e Ch 11]