• 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).
o Suggests optic nerve or severe retinal disease.
o Swinging light test: affected pupil dilates when light moved onto it.
o Small, irregular, accommodates but does not react to light ("prostitute's pupil").
o Cause: neurosyphilis (tabes dorsalis), diabetes.
o Miosis (constricted pupil), partial ptosis, anhidrosis ± enophthalmos.
o Causes: carotid dissection, Pancoast tumor, brainstem lesion, syringomyelia.
• 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).
• 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.
• 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.
• 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.
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Author & Educational Disclaimer
Author:
Dr Phillip Cockrell BM FRCP DipClinEd
Dr Phillip Cockrell is a UK Consultant Physician in Internal Medicine, currently working at Queen Alexandra Hospital, Portsmouth University Hospitals NHS Trust. He has previously worked as a registrar across Intensive Care Medicine, Gastroenterology, Cardiology, Stroke Medicine, Acute Medicine, and Respiratory Medicine.
He has held senior leadership roles including Associate Clinical Director of the Acute Medical Unit, Clinical Director of Internal Medicine, and Chief of Medicine. Dr Cockrell has over 15 years’ experience in postgraduate medical education, having lectured extensively across the MRCP syllabus and contributed to MRCP revision teaching and course development.
Dr Cockrell holds a Bachelor of Medicine (BM), Fellowship of the Royal College of Physicians (FRCP), and a Diploma in Clinical Education (DipClinEd). His teaching approach is based on structured consolidation of complex medical topics to support efficient and effective revision for postgraduate examinations.
Purpose of this content:
The material on this page is intended solely for educational purposes to support revision for the MRCP (UK) Part 1 examination. It reflects examination-relevant principles of internal medicine and is designed to aid learning and pattern recognition.
Medical disclaimer:
This content is designed for postgraduate medical examination revision and does not constitute medical advice, diagnosis, or treatment guidance and must not be used as a substitute for professional clinical judgement, local guidelines, or specialist consultation. Clinical decisions should always be made in the context of individual patient circumstances and current national guidance.
