⚡ What are the four levels of visual pathway lesions?
T1: Anterior eye/outer retina/choroid; T2: Optic nerve/inner retina; T3: Optic chiasm; T4: Retrochiasmal pathway (optic tracts, radiations, visual cortex).
What kind of visual field defects occur at the optic chiasm?
Bitemporal field defects (heteronymous), respecting the vertical midline.
What kind of visual field defects occur with retrochiasmal lesions?
Homonymous field defects; the more posterior the lesion, the more congruous the defect.
⚡ What is the most common cause of chiasmal disease?
Compression of the chiasm by pituitary gland tumours.
What are the typical visual signs of chiasmal compression?
Progressive bitemporal visual field loss, possible VA reduction if macular fibres affected, colour desaturation, and sometimes diplopia from CN III/IV/VI involvement.
What is Pituitary Apoplexy?
Sudden haemorrhagic infarction of a pituitary adenoma causing severe headache, vision loss, ptosis, and ophthalmoplegia. Requires emergency admission.
What is the management for pituitary lesions compressing the chiasm?
Urgent referral for neuroimaging and surgical decompression. Regular visual field monitoring for recurrence.
⚡ What is a Pituitary Chromophobe Adenoma?
Most common tumour affecting the chiasm. Secretes prolactin → amenorrhoea, infertility, galactorrhoea in women; impotence, gynaecomastia in men.
What is a Craniopharyngioma?
Slow-growing tumour from Rathke’s pouch remnants; causes IT then ST field loss by compressing the chiasm from above and behind.
What is a Tuberculum Sellae Meningioma?
Compresses junction of optic nerve and chiasm, causing junctional scotoma.
What is a Sphenoid Ridge Meningioma?
Compresses optic nerve (ON) early if medial; later if lateral. Causes proptosis and hyperostosis.
What is a Foster Kennedy Syndrome?
Optic atrophy in one eye and papilloedema in the fellow eye due to olfactory groove meningioma.
What kind of field defect is caused by internal carotid aneurysm?
Binasal hemianopia, worse on the side of the aneurysm.
⚡ What are the main causes of retrochiasmal visual pathway disease?
Stroke (most common), brain tumour, MS, infection (TB), or vascular malformation.
What is a Wernicke Hemianopic Pupil?
Pupil light reflex absent when affected half of retina is stimulated (optic tract lesion).
What field defect results from temporal lobe (Meyer’s loop) lesion?
Contralateral superior quadrantanopia – ‘pie in the sky’.
What field defect results from parietal lobe lesion?
Contralateral inferior quadrantanopia – ‘pie on the floor’.
What lesion causes macular sparing?
Occipital cortex lesion supplied by posterior cerebral artery, with macular area supplied by middle cerebral artery.
What are key features of occipital lobe lesions?
Congruous homonymous hemianopia, macular sparing, formed visual hallucinations, Riddoch phenomenon (perceive moving but not stationary targets).
What is the management of retrochiasmal lesions?
Urgent neuroimaging and neuro-ophthalmology referral. Low vision rehabilitation for field defects.
⚡ What is the role of PPRF?
Horizontal gaze centre in pons that connects to ipsilateral CN VI nucleus and contralateral CN III via MLF for conjugate horizontal gaze.
What is the role of riMLF?
Vertical gaze centre controlling subnuclei of muscles for upgaze and downgaze.
What are supranuclear ophthalmoplegias?
Gaze palsies where voluntary eye movements (saccades, pursuit) are affected but vestibulo-ocular reflex (VOR) preserved.
⚡ What is Parinaud’s Syndrome?
Dorsal midbrain syndrome with upgaze/downgaze palsy, Collier’s sign (lid retraction), convergence-retraction nystagmus, and light-near dissociation.
