Neuro-optometry
Core framework
Neuro-optometry questions test localization of lesions along the visual pathway and recognition of optic nerve disease. Know the visual field defect that corresponds to each lesion site.
Concepts to know cold
- Pathway: retina to optic nerve to chiasm to optic tract to lateral geniculate to optic radiations to occipital cortex. Chiasm lesions produce bitemporal defects; retrochiasmal lesions produce homonymous defects.
- Optic neuritis: painful vision loss, afferent pupillary defect, color desaturation. Associated with multiple sclerosis.
- Papilledema: bilateral disc swelling from raised intracranial pressure; vision often preserved early.
- Pupil testing: afferent pupillary defect indicates asymmetric optic nerve dysfunction; Horner syndrome (ptosis, miosis, anhidrosis) localizes along sympathetic chain.
Traps
Do not confuse papilledema (bilateral, preserved acuity) with optic neuritis (usually unilateral, acuity loss, pain). Remember that a homonymous hemianopia localizes retrochiasmally; a bitemporal defect localizes to the chiasm.
Rule of thumb
Map the field defect to the lesion: bitemporal = chiasm; homonymous = retrochiasmal; central scotoma with APD = optic nerve.
Worked example
A patient has a right homonymous hemianopia. The defect respects the vertical midline and affects the right side of each field, localizing to the left retrochiasmal pathway (optic tract, radiations, or occipital cortex).