Visual field defects

•    Optic nerve lesion

o    Monocular vision loss.

o    Examples: optic neuritis, ischemic optic neuropathy, severe glaucoma.

•    Optic chiasm lesion

o    Bitemporal hemianopia (loss of temporal fields).

o    Classic cause: pituitary adenoma.

o    Others: craniopharyngioma (children), meningioma.

•    Optic tract lesion

o    Contralateral homonymous hemianopia.

o    Relative afferent pupillary defect (RAPD) on side opposite lesion.

•    Temporal lobe (Meyer's loop) lesion

o    Contralateral superior quadrantanopia ("pie in the sky").

o    Cause: temporal lobe epilepsy, tumor.

•    Parietal lobe lesion

o    Contralateral inferior quadrantanopia ("pie on the floor").

•    Occipital lobe lesion

o    Contralateral homonymous hemianopia, often macular sparing (due to dual blood supply from PCA and MCA).

Pupil abnormalities

•    RAPD (Marcus Gunn pupil)

o    Suggests optic nerve or severe retinal disease.

o    Swinging light test: affected pupil dilates when light moved onto it.

•    Argyll Robertson pupil

o    Small, irregular, accommodates but does not react to light ("prostitute's pupil").

o    Cause: neurosyphilis (tabes dorsalis), diabetes.

•    Horner’s syndrome

o    Miosis (constricted pupil), partial ptosis, anhidrosis ± enophthalmos.

o    Causes: carotid dissection, Pancoast tumor, brainstem lesion, syringomyelia.

Oculomotor (CN III) palsy

•    Eye "down and out" (unopposed LR and SO), ptosis.

•    Pupil-involving: usually compressive (e.g., posterior communicating artery aneurysm) → urgent neurosurgical referral.

•    Pupil-sparing: microvascular (diabetes, hypertension).

Internuclear ophthalmoplegia (INO)

•    Failure of adduction in ipsilateral eye on lateral gaze.

•    Nystagmus of contralateral abducting eye.

•    Convergence typically preserved.

•    Causes:

o    Young: multiple sclerosis.

o    Older: brainstem stroke.

Nystagmus

•    Peripheral vestibular nystagmus

o    Horizontal or rotatory.

o    Suppressed by visual fixation.

o    Associated with vertigo, tinnitus, hearing loss.

•    Central nystagmus

o    Can be vertical, direction-changing.

o    Not suppressed by fixation.

o    Suggests brainstem or cerebellar pathology.

Cavernous sinus syndrome

•    Involves CN III, IV, VI (all extraocular movements), and V1, V2 (sensory forehead, midface).

•    May include Horner’s (sympathetic fibre involvement).

•    Causes:

o    Thrombosis (sepsis, sinus infection)

o    Carotid-cavernous fistula

o    Tumors (pituitary adenoma extension, meningioma)

Extra Revision Pearls

•    Bitemporal hemianopia clue → pituitary adenoma.

•    "Down and out" pupil clue → CN III palsy (check pupil!).

•    INO clue → young woman → think MS.

•    Painful ophthalmoplegia clue → cavernous sinus syndrome.

•    Macular sparing clue → occipital lobe lesion.