A 28-year-old woman presents with acute unilateral vision loss, colour vision defect (3/14 Ishihara plates), central scotoma, and retro-orbital pain worsening with eye movement. MRI shows enhancement of the intraorbital optic nerve and periventricular T2 lesions with gadolinium enhancement. Fundoscopy of the affected eye reveals the appearance marked **A** in the diagram. Which of the following best describes the pathophysiological significance of the finding marked **A** in this clinical context?
A. It represents posterior optic neuritis with retrobulbar inflammation, explaining the preserved visual acuity and normal fundoscopic appearance
B. It suggests acute angle-closure glaucoma with secondary optic nerve swelling and requires immediate gonioscopy and laser peripheral iridotomy
C. It reflects chronic papilloedema from intracranial hypertension, requiring urgent neuroimaging to exclude space-occupying lesion
D. It indicates anterior optic neuritis with demyelination of the optic nerve head, consistent with clinically isolated syndrome and high risk of conversion to multiple sclerosis
Explanation
Why "It indicates anterior optic neuritis with demyelination of the optic nerve head, consistent with clinically isolated syndrome and high risk of conversion to multiple sclerosis" is right
The finding marked A — hyperaemic, swollen optic disc with blurred margins — is the hallmark of anterior optic neuritis. In this case, the clinical presentation (acute unilateral vision loss, colour vision defect, central scotoma, retro-orbital pain worse with eye movement, RAPD, and MRI evidence of optic nerve enhancement with periventricular demyelinating lesions and oligoclonal bands) is pathognomonic for demyelinating optic neuritis associated with multiple sclerosis. According to Kanski's Clinical Ophthalmology, anterior optic neuritis presents with visible disc swelling and hyperaemia because the inflammation involves the optic nerve head itself, distinguishing it from retrobulbar neuritis where the fundus appears normal. The presence of periventricular T2 hyperintensities and gadolinium-enhancing lesions on MRI, combined with oligoclonal bands in CSF, establishes this as a clinically isolated syndrome with high risk of conversion to MS.
Why each distractor is wrong
"It represents posterior optic neuritis with retrobulbar inflammation, explaining the preserved visual acuity and normal fundoscopic appearance": This is internally contradictory and factually incorrect. Posterior (retrobulbar) optic neuritis presents with a normal fundus and preserved visual acuity initially; the patient here has markedly reduced acuity (6/36) and visible disc swelling. The finding marked A is not normal — it is hyperaemic and swollen.
"It suggests acute angle-closure glaucoma with secondary optic nerve swelling and requires immediate gonioscopy and laser peripheral iridotomy": Acute angle-closure glaucoma presents with severe pain, halos, corneal oedema, mid-dilated pupil, and elevated intraocular pressure. This patient has normal intraocular pressures, clear anterior segment, and no halos. The clinical context (retro-orbital pain, colour vision loss, RAPD, MRI evidence of demyelination) is entirely inconsistent with glaucoma.
"It reflects chronic papilloedema from intracranial hypertension, requiring urgent neuroimaging to exclude space-occupying lesion": Papilloedema is typically bilateral, progressive, and associated with headache, vomiting, and visual obscurations. This patient has unilateral disc swelling, no headache or vomiting, and MRI has already been performed showing demyelinating lesions rather than a mass. The acute presentation with colour vision loss and central scotoma is characteristic of optic neuritis, not papilloedema.
High-YieldNEET PG
Anterior optic neuritis shows visible disc hyperaemia and swelling; retrobulbar neuritis has a normal fundus despite severe vision loss. The presence of demyelinating lesions on MRI and oligoclonal bands in CSF confirms MS-associated optic neuritis.
Kanski's Clinical Ophthalmology, 9th Edition, Chapter on Neuro-ophthalmology
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