OP9.5 | Optic Nerve and Visual Pathway Disorders — Summary & Reflection

KEY TAKEAWAYS

The visual pathway from retina to occipital cortex produces characteristic field defects that localise lesions anatomically: monocular visual loss = optic nerve (prechiasmal); bitemporal hemianopia = chiasmal compression (most commonly pituitary macroadenoma); homonymous hemianopia = retrochiasmal (tract/radiation/cortex). Optic disc disorders include: papilloedema (bilateral, raised ICP, VA initially normal, no RAPD — do MRI before LP; treat IIH with acetazolamide, weight loss); optic neuritis (unilateral, painful eye movement, young adult, MS association, RAPD, colour loss — IV methylprednisolone hastens recovery, does not improve 1-year VA, no oral prednisone alone); arteritic AION from GCA (elderly, ESR/CRP elevated, sudden profound loss, bilateral emergency — immediate high-dose IV methylprednisolone, do not await biopsy); non-arteritic AION (atherosclerotic risk factors, 'disc at risk', altitudinal loss, no proven treatment); optic atrophy (primary = sharp pale disc from glaucoma/compression/toxic; secondary = post-papilloedema). Investigations: RAPD (bedside, 10 seconds), colour vision (Ishihara — most sensitive for optic nerve disease), VEP (prolonged P100 in optic neuritis/MS), MRI brain/orbits (gold standard). Cortical blindness from bilateral PCA infarction produces total blindness with intact pupillary reflexes — because the pupillary pathway branches off at the optic tract before the cortex.

REFLECT

Reflect on the following:
- The swinging flashlight test (RAPD) is a completely free bedside test that takes 10 seconds and yields enormous diagnostic information. Why do you think this test is often omitted in clinical practice, and how would you make it a habit in your own examination routine?
- Consider a 28-year-old patient who has just received a diagnosis of optic neuritis and has been told she has a high risk of developing multiple sclerosis. She is anxious and asks: 'Will I go blind? Will I be in a wheelchair?' How would you counsel her using the actual evidence from the ONTT trial and current MS disease-modifying therapies?
- If you were a physician in a rural district hospital with no MRI and no ophthalmologist on site, and a patient presents with sudden visual loss and temporal headache with jaw pain in a 75-year-old, what would you do? What is the risk of waiting 48 hours for a hospital transfer?
- Visual field testing at the bedside (confrontation fields) is routinely omitted in general medicine ward rounds. Given what you now know about the conditions detectable by visual field testing — bitemporal hemianopia, homonymous hemianopia, papilloedema — argue for or against making it a standard part of the neurological examination.