13 EYE SYMPTOMS & SIGNS
👩⚕️ Study tip: almost every MRCS Part A eye question is really a neuroanatomy question. Learn the visual pathway and the localising signs of pupil, lid and gaze, and the rest follows.
The visual pathway
Each level has a signature field defect — place the lesion, pick the answer.
➡ Retina / optic nerve ➡ ipsilateral monocular visual loss
➡ Optic chiasm ➡ bitemporal hemianopia (crossing nasal fibres)
➡ Optic tract / LGN ➡ contralateral homonymous hemianopia (no macular sparing; often with RAPD)
➡ Meyer's loop (temporal lobe) ➡ contralateral superior quadrantanopia ("pie in the sky")
➡ Baum's loop (parietal lobe) ➡ contralateral inferior quadrantanopia ("pie on the floor")
➡ Occipital cortex (PCA stroke) ➡ contralateral homonymous hemianopia with macular sparing
PITS mnemonic: Parietal = Inferior; Temporal = Superior. The defect is always contralateral — a right temporal lesion gives a left superior quadrantanopia.
👩⚕️ Macular sparing: the occipital pole has dual PCA/MCA blood supply. A PCA stroke spares central vision; a complete radiation lesion does not.
👩⚕️ Surgical relevance: Meyer's loop extends within 5 cm of the temporal pole — at risk during anterior temporal lobectomy for epilepsy.
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Chiasmal compression: who pushes from where
| Compresses from | Lesion | Field onset |
|---|---|---|
| Below | Pituitary adenoma (commonest) | Upper temporal quadrants first |
| Above | Craniopharyngioma, 3rd ventricle tumour | Lower temporal quadrants first |
| Lateral | ICA aneurysm | Asymmetrical / nasal defects |
A pituitary macroadenoma hits inferior nasal fibres first (they loop low through the chiasm) — upper temporal fields go first.
Pupillary abnormalities
The pupil has two opposing controls: parasympathetic (CN III → Edinger–Westphal → ciliary ganglion → sphincter pupillae) and sympathetic (three-neurone chain → dilator pupillae).
Horner's syndrome — the sympathetic chain
Triad: miosis, partial ptosis, anhidrosis (± enophthalmos). Localise the lesion by the three-neurone anatomy:
| Order | Path | Anhidrosis | Classic causes |
|---|---|---|---|
| 1st (central) | Hypothalamus → ciliospinal centre of Budge (C8–T2) | Face, arm, trunk | Brainstem stroke (lateral medullary / Wallenberg), MS, syringomyelia |
| 2nd (preganglionic) | T1 root → over lung apex → stellate ganglion | Face only | Pancoast tumour, cervical rib, thyroidectomy, trauma |
| 3rd (postganglionic) | Superior cervical ganglion → along ICA → orbit | None (sweat fibres travel with ECA) | Internal carotid artery dissection, cluster headache, cavernous sinus lesion |
👩⚕️ Exam pearl: painful Horner's in a young patient after neck trauma or chiropractic manipulation = ICA dissection until proven otherwise — CT/MR angiogram urgently. Painless Horner's with a smoker and shoulder pain = Pancoast tumour.
Other pupillary signs
➡ Adie tonic pupil ➡ dilated, sluggish to constrict and redilate. Postganglionic parasympathetic (ciliary ganglion) lesion. Young women; ± absent reflexes (Holmes–Adie).
➡ Argyll Robertson ➡ small, irregular, accommodates but does not react. Neurosyphilis (also diabetes). "Prostitute's pupil."
➡ Marcus Gunn (RAPD) ➡ both pupils dilate when light swings to the affected eye. Afferent optic nerve defect — optic neuritis, ischaemic optic neuropathy, dense detachment.
➡ CN III palsy ➡ fixed dilated pupil, ptosis, "down and out". Surgical causes (PCom aneurysm, uncal herniation) blow the pupil; medical microvascular causes (diabetes) spare it — pupillary fibres run superficially on pial vessels.
👩⚕️ Argyll Robertson = Accommodation Retained. Adie is sluggish to both.
Ptosis
| Cause | Mechanism | Pupil | Clue |
|---|---|---|---|
| CN III palsy | Levator (LPS) denervated | Dilated (if surgical) | "Down and out", complete ptosis |
| Horner's | Müller's muscle denervated | Constricted | Partial ptosis (Müller's lifts only 2 mm) |
| Myasthenia gravis | NMJ fatigue | Normal | Fatigable, diplopia |
| Levator dehiscence | Aponeurosis stretched | Normal | Age, contact lens wearers |
Eye movement disorders
Internuclear ophthalmoplegia (INO) — lesion of the medial longitudinal fasciculus (MLF), which links abducens to contralateral oculomotor nuclei.
- On lateral gaze: adducting eye fails to cross the midline.
- Abducting eye nystagmus.
- Convergence preserved (medial recti work — just not conjugately).
MS in young patients (often bilateral); brainstem stroke in older patients (unilateral).
One-and-a-half syndrome — PPRF + ipsilateral MLF lesion. Ipsilateral eye cannot move horizontally at all ("one"); contralateral eye can only abduct ("half"). Only one functioning horizontal movement remains.
The acute red eye
| Condition | Pain | Vision | Pupil | Key feature |
|---|---|---|---|---|
| Acute angle-closure glaucoma | Severe + vomiting | Reduced, haloes | Mid-dilated, fixed, oval | Hazy cornea, stony-hard globe — emergency |
| Anterior uveitis | Aching, photophobia | Mildly reduced | Small, irregular | Ciliary flush, hypopyon; HLA-B27 (AS, IBD) |
| Scleritis | Boring, worse at night | May be reduced | Normal | Bluish hue; rheumatoid arthritis, vasculitis |
| Bacterial conjunctivitis | Gritty | Normal | Normal | Purulent discharge |
| Viral conjunctivitis | Gritty | Normal | Normal | Watery + preauricular node |
| Subconjunctival haemorrhage | None | Normal | Normal | Flat red patch; benign |
👩⚕️ Acute angle-closure glaucoma: long-sighted older woman, pupil semi-dilated in a dim cinema. Treatment: lie flat, IV acetazolamide, pilocarpine + topical beta-blocker, then laser iridotomy. Do not dilate.
Sudden painless vision loss
| Condition | Fundoscopy | Key association |
|---|---|---|
| CRAO | Pale retina, cherry-red spot | Carotid emboli, GCA — treat as stroke |
| CRVO | "Stormy sunset" — flame haemorrhages, dilated tortuous veins | Hypertension, glaucoma, hyperviscosity |
| Amaurosis fugax | Normal between attacks | "Curtain coming down" — TIA of the eye; urgent carotid Doppler |
| Retinal detachment | Tobacco dust, detached retina | Flashes/floaters then curtain; myopia, trauma |
| Vitreous haemorrhage | Loss of red reflex | Proliferative diabetic retinopathy, PVD |
| Wet AMD | Drusen, subretinal haemorrhage | Central scotoma, distortion of straight lines |
👩⚕️ CRAO = stroke of the eye. Cherry-red spot = thin macula showing intact choroid beneath an infarcted retina. Over 50: exclude giant cell arteritis (ESR, CRP, temporal biopsy) and start high-dose steroids immediately to save the other eye.
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Test yourself
An injury to the parietal lobe will most likely cause which visual field defect?
- ((Optic nerve lesion — monocular visual loss::Wrong level; optic nerve damage is ipsilateral and monocular.))
- ((Optic chiasm — bitemporal hemianopia::Chiasmal lesion (pituitary adenoma), not parietal.))
- ((Lateral geniculate body — homonymous hemianopia::LGN lesions give a full hemianopia, not a quadrantanopia.))
- ((Baum's loop — contralateral inferior quadrantanopia::☑️ Parietal radiation carries lower visual field — "pie on the floor".))
- ((Meyer's loop — contralateral superior quadrantanopia::Meyer's loop runs through the temporal lobe, not parietal.))
👩⚕️ PITS: Parietal = Inferior, Temporal = Superior.
A patient has homonymous hemianopia with no macular sparing. Where is the lesion?
- ((Meyer's loop::Gives superior quadrantanopia, not full hemianopia.))
- ((Optic nerve::Causes monocular loss, not homonymous defect.))
- ((Optic chiasm::Causes bitemporal hemianopia from crossing nasal fibres.))
- ((Optic tract::☑️ Lesion behind chiasm, before LGN — no macular sparing; often with contralateral RAPD.))
- ((Occipital cortex::PCA stroke here spares the macula via dual MCA/PCA supply.))
👩⚕️ Optic tract lesions are the only pathway lesion that can give a contralateral RAPD.
Homonymous hemianopia with macular sparing after a stroke — where is the lesion?
- ((Optic radiation::A complete radiation lesion does not spare the macula.))
- ((Optic chiasm::Would give bitemporal, not homonymous.))
- ((Occipital cortex (PCA stroke)::☑️ Dual PCA/MCA supply to the occipital pole spares central vision.))
- ((Pituitary gland::Chiasmal compression gives bitemporal hemianopia.))
- ((Optic tract::Homonymous but without macular sparing.))
A 45-year-old woman has progressive bitemporal hemianopia and raised prolactin. Most likely diagnosis?
- ((Craniopharyngioma::Typically childhood, calcified, arises from Rathke's pouch; compresses from above.))
- ((Optic nerve glioma::Causes unilateral loss and proptosis.))
- ((Pituitary adenoma (prolactinoma)::☑️ Compresses chiasm from below; raised prolactin confirms.))
- ((Tuberculum sellae meningioma::Can compress chiasm but does not raise prolactin.))
- ((ICA aneurysm::Compresses laterally, causing asymmetrical or nasal defects.))
👩⚕️ Pituitary pushes up → upper temporal fields go first. Craniopharyngioma pushes down → lower fields first.
A left RAPD (Marcus Gunn pupil) on swinging-flashlight test indicates:
- ((Left optic tract lesion::Tract lesions can cause a contralateral RAPD, but the mechanism differs.))
- ((Left optic nerve lesion::☑️ Reduced afferent signal — both pupils dilate when light swings to the bad eye.))
- ((Left CN III palsy::That is an efferent defect — fixed dilated pupil.))
- ((Left occipital cortex lesion::Cortex is not in the reflex arc — pupillary response preserved.))
- ((Left Horner's syndrome::Sympathetic lesion — miosis and ptosis, no afferent defect.))
👩⚕️ Pupillary reflex bypasses the cortex: retina → optic nerve → pretectal nucleus → bilateral EW nuclei → CN III.
A right PCA stroke produces which visual field defect?
- ((Right homonymous hemianopia::Right cortex serves the left field — defect would be on the left.))
- ((Bitemporal hemianopia::Requires chiasmal damage.))
- ((Left homonymous hemianopia with macular sparing::☑️ Right occipital cortex infarct; macula spared by MCA collateral.))
- ((Left superior quadrantanopia::That is a temporal lobe (Meyer's loop) lesion.))
- ((Bilateral cortical blindness::Needs bilateral PCA occlusion.))
Right temporal lobe tumour — expected visual field defect?
- ((Right inferior quadrantanopia::Right lobe serves left visual field; "ipsilateral" defects do not occur.))
- ((Bitemporal hemianopia::Chiasmal lesion.))
- ((Left homonymous hemianopia::Implies complete tract or radiation lesion.))
- ((Left superior quadrantanopia::☑️ Meyer's loop disrupted — "pie in the sky".))
- ((Left inferior quadrantanopia::Parietal (Baum's loop) lesion.))
👩⚕️ Anterior temporal lobectomy for epilepsy: classic operation that risks this defect. Meyer's loop reaches within 5 cm of the temporal pole.
A 60-year-old smoker has right-sided shoulder pain, miosis and partial ptosis on the right with facial anhidrosis. Most likely cause?
- ((Lateral medullary stroke::1st-order Horner's — anhidrosis would extend to arm and trunk, plus brainstem signs.))
- ((Pancoast tumour::☑️ 2nd-order Horner's from apical lung tumour invading the sympathetic chain at T1.))
- ((Internal carotid artery dissection::3rd-order Horner's — no anhidrosis (sweat fibres travel with ECA).))
- ((Cluster headache::3rd-order Horner's, episodic and painful, no anhidrosis.))
- ((Cavernous sinus thrombosis::3rd-order Horner's plus CN III/IV/VI palsies, proptosis.))
👩⚕️ Face-only anhidrosis localises to 2nd-order (preganglionic); no anhidrosis = 3rd-order (postganglionic, along ICA).
A small, irregular pupil that accommodates but does not react to light suggests:
- ((Adie tonic pupil::Dilated, sluggish to both light and accommodation.))
- ((Horner's syndrome::Small but reactive; with ptosis and anhidrosis.))
- ((CN III palsy::Fixed dilated pupil, "down and out" eye.))
- ((Argyll Robertson pupil::☑️ Accommodates but does not react — classical for neurosyphilis.))
- ((Marcus Gunn pupil::An afferent defect on swinging-light test; pupil is not structurally abnormal.))
👩⚕️ "Accommodation Retained" = Argyll Robertson. Prostitute's pupil — accommodates but doesn't react.
An elderly woman presents with a painful red right eye, vomiting and haloes around lights. The cornea is hazy and the pupil is mid-dilated and unreactive. Diagnosis?
- ((Anterior uveitis::Small, irregular pupil; ciliary flush; not the hard globe.))
- ((Bacterial conjunctivitis::Purulent discharge, normal vision, no pain.))
- ((Scleritis::Boring pain worse at night, bluish hue, normal pupil.))
- ((Acute angle-closure glaucoma::☑️ Mid-dilated fixed pupil, hazy cornea, stony-hard globe — emergency.))
- ((Subconjunctival haemorrhage::Painless, flat red patch, normal vision.))
👩⚕️ Lie flat, IV acetazolamide, pilocarpine, beta-blocker drops, then laser iridotomy. Never dilate.
A 70-year-old presents with sudden painless loss of vision in the right eye. Fundoscopy shows a pale retina with a cherry-red spot at the macula. The most important next step is:
- ((Intravitreal anti-VEGF injection::Treatment for wet AMD, not CRAO.))
- ((Laser photocoagulation::Used in proliferative diabetic retinopathy or retinal tears.))
- ((Check ESR/CRP and start high-dose steroids if GCA suspected::☑️ CRAO over 50 — exclude giant cell arteritis to protect the other eye.))
- ((Reassurance and review in clinic::Sight-threatening emergency; never reassure.))
- ((Topical timolol::A glaucoma drug; not relevant here.))
👩⚕️ CRAO = stroke of the eye. Cherry-red spot = thin macula showing the intact choroid against an infarcted retina.
Revision summary
➡ Pathway field defects: monocular (nerve) → bitemporal (chiasm) → homonymous (tract/LGN) → quadrantanopia (radiation, PITS) → homonymous with macular sparing (occipital/PCA).
➡ Macular sparing = occipital cortex (dual PCA/MCA supply).
➡ Pituitary pushes up → upper temporal fields first. Craniopharyngioma pushes down → lower fields first.
➡ Horner's: miosis + partial ptosis + anhidrosis. Localise by anhidrosis pattern — face + arm (1st), face only (2nd, Pancoast), none (3rd, ICA dissection).
➡ Argyll Robertson = Accommodates, doesn't React → neurosyphilis. Adie = tonic, sluggish, young woman.
➡ RAPD (Marcus Gunn) = afferent / optic nerve defect.
➡ CN III palsy: surgical (compressive, e.g. PCom aneurysm) blows the pupil; medical (diabetic) spares it.
➡ INO = MLF lesion → adducting eye fails, abducting eye nystagmus, convergence preserved. MS in young, stroke in old.
➡ Acute angle-closure glaucoma: mid-dilated fixed pupil, hazy cornea, vomiting — emergency.
➡ CRAO = cherry-red spot; always exclude GCA in over-50s.
➡ Amaurosis fugax = TIA of the eye → carotid Doppler.