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MBBS Ophthalmology — Complete Q&A

Topics: Retina | Neuro-Ophthalmology | Optics

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PART A: OPTICS

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1. Basic Optics

• Cornea contributes ~+43 D (major contribution).
• Lens contributes ~+15–16 D (at rest); up to ~+29 D max during accommodation.
  (Guyton & Hall, Textbook of Medical Physiology)

• Far point: The point at which the eye is focused when accommodation is completely relaxed. For emmetropia = infinity.
• Near point: The closest point at which the eye can focus with maximum accommodation. Recedes with age (presbyopia).

1. Ciliary muscle contracts (ring-like)
2. Tension on zonule fibres (suspensory ligaments of lens) relaxes
3. Elastic lens becomes more convex/spherical
4. Refractive power of lens increases Controlled by parasympathetic fibres via CN III → ciliary ganglion → short ciliary nerves.

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2. Errors of Refraction — Detailed

• Axial myopia — most common; elongated antero-posterior axis
• Refractive/Curvature myopia — excessive corneal/lens curvature
• Index myopia — increased refractive index of lens (e.g., nuclear sclerosis)
• Positional — anterior displacement of lens
• Spasm of accommodation

• Lattice degeneration → retinal detachment
• Posterior staphyloma
• Macular haemorrhage / Fuchs spot (pigmented scar at macula)
• Myopic maculopathy / chorioretinal atrophy
• Open-angle glaucoma (3× risk)
• Vitreous degeneration / floaters
• Cataract (nuclear type, earlier onset)

• Latent — corrected by accommodation; not evident on routine testing
• Facultative — can be overcome by accommodation but with effort
• Manifest — cannot be fully overcome
• Total = manifest + latent (revealed under cycloplegia)
• Absolute — cannot be overcome even with maximum accommodation

• Regular astigmatism: two principal meridians perpendicular to each other
  • With-the-rule: vertical meridian more curved (corrected with + cylinder at 90°)
  • Against-the-rule: horizontal meridian more curved (+ cylinder at 180°)
  • Oblique: principal meridians at neither 90° nor 180°
• Irregular astigmatism: no two principal meridians; seen in keratoconus, corneal scarring — corrected with hard contact lens

• Aniseikonia (image size difference)
• Suppression of the more ametropic eye
• Amblyopia (lazy eye) — especially if uncorrected in childhood

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PART B: RETINA

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3. Anatomy & Physiology of the Retina

1. Internal limiting membrane (ILM)
2. Nerve fibre layer (axons of ganglion cells)
3. Ganglion cell layer
4. Inner plexiform layer
5. Inner nuclear layer (bipolar, amacrine, horizontal cells)
6. Outer plexiform layer
7. Outer nuclear layer (photoreceptor nuclei)
8. External limiting membrane
9. Photoreceptor layer (rods and cones)
10. Retinal pigment epithelium (RPE)

• Cone adaptation: fast, complete in 5–7 minutes
• Rod adaptation: slow, complete in ~25–30 minutes (rhodopsin regeneration) Overall sensitivity increases ~100,000×. Vitamin A deficiency impairs rhodopsin regeneration → night blindness.

• Macula lutea: central area of retina ~5.5 mm diameter, temporal to disc; contains xanthophyll pigment (yellow). Site of highest visual acuity.
• Fovea centralis: central depression of macula, ~1.5 mm wide; contains only cones (no rods, no capillaries, no inner layers).
• Foveola: central pit of fovea, ~0.35 mm, densest cone packing; responsible for 6/6 vision.

• Inner 2/3 of retina: Central retinal artery (branch of ophthalmic artery, branch of ICA). Supplies via capillary network.
• Outer 1/3 (photoreceptors + RPE): Choriocapillaris (short posterior ciliary arteries) — avascular zone of fovea nourished by diffusion from choroid.
• Blood-retinal barrier: Tight junctions of retinal capillary endothelium (inner) and RPE (outer).

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4. Diabetic Retinopathy

Non-Proliferative Diabetic Retinopathy (NPDR)

• Mild NPDR: microaneurysms only
• Moderate NPDR: microaneurysms + dot/blot haemorrhages, hard exudates, cotton-wool spots (CWS)
• Severe NPDR (4-2-1 rule / ETDRS rule):

  • 20 haemorrhages in all 4 quadrants, OR

  • Venous beading in ≥2 quadrants, OR
  • Intraretinal microvascular abnormalities (IRMA) in ≥1 quadrant

Proliferative Diabetic Retinopathy (PDR)

• New vessels on disc (NVD) or elsewhere (NVE)
• Pre-retinal/vitreous haemorrhage
• Tractional retinal detachment
• Rubeosis iridis → neovascular glaucoma

Diabetic Maculopathy

• Clinically significant macular oedema (CSMO) — most common cause of visual loss in NPDR in type 2 DM

• 4: >20 haemorrhages in 4 quadrants
• 2: venous beading in ≥2 quadrants
• 1: IRMA in ≥1 quadrant 50% risk of developing PDR within 1 year if untreated.

• Retinal thickening within 500 μm of centre of fovea
• Hard exudates within 500 μm of fovea with adjacent retinal thickening
• Retinal thickening ≥1 disc area within 1 disc diameter of fovea

• Prevention: glycaemic control (HbA1c <7%), BP control, lipid control
• CSMO: Intravitreal anti-VEGF (bevacizumab, ranibizumab, aflibercept) — first-line; focal/grid laser photocoagulation
• PDR: Panretinal photocoagulation (PRP / scatter laser) — 1200–1600 burns; intravitreal anti-VEGF
• Vitreous haemorrhage / TRD: Pars plana vitrectomy

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5. Hypertensive Retinopathy

• Copper wire: Increased light reflex due to mild arteriolar wall thickening — orange-red appearance
• Silver wire: Severe arteriolar sclerosis with almost opaque walls — white/silver appearance

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6. Retinal Vascular Occlusions

• Sudden, painless, profound loss of vision (may retain some light perception via cilioretinal artery in 25%)
• RAPD (relative afferent pupillary defect) present
• Fundus: milky white oedema of entire retina + cherry-red spot at fovea (choroidal blush visible through thin fovea while surrounding ischaemic retina is white)
• Retinal arteries: attenuated, "box-carring" of blood column
• Aetiology: embolism (commonest — carotid atheroma, cardiac), thrombosis, arteritis (GCA)
• Investigation: ESR/CRP (rule out GCA), carotid Doppler, ECHO
• Treatment: Emergency (within 90–100 min): ocular massage, AC paracentesis, carbogen inhalation, IV acetazolamide, thrombolytics (limited evidence). Long-term: antiplatelet, risk factor modification.

• Vascular: CRAO (most common clinical cause)
• Storage disorders (sphingolipidoses):
  • Tay-Sachs disease (GM2 gangliosidosis)
  • Niemann-Pick disease
  • Gaucher disease (rare)
  • Sandhoff disease
  • Farber disease

• Ischaemic CRVO (25%): >10 disc areas of retinal ischaemia on FA; VA usually <6/60; RAPD may be present; risk of rubeosis (neovascular glaucoma) at 3 months ("90-day glaucoma"); massive haemorrhages in all 4 quadrants
• Non-ischaemic CRVO (75%): fewer haemorrhages; VA relatively preserved; may resolve spontaneously; can progress to ischaemic
• Fundus: "blood and thunder" — flame haemorrhages in all 4 quadrants, dilated tortuous veins, disc oedema, CWS
• Risk factors: hypertension (most common), hyperlipidaemia, diabetes, hypercoagulability, glaucoma, hyperviscosity

• Macular oedema: Intravitreal anti-VEGF (ranibizumab, aflibercept) or intravitreal dexamethasone implant (Ozurdex)
• Rubeosis iridis: PRP + intravitreal anti-VEGF
• Underlying risk factor management

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7. Age-Related Macular Degeneration (ARMD)

Dry (Non-exudative) ARMD — 85–90%

• Drusen: small (hard) or large (soft) extracellular deposits between RPE and Bruch's membrane
• Geographic atrophy: loss of RPE + photoreceptors; gradual central visual loss

Wet (Exudative/Neovascular) ARMD — 10–15%, but 80–90% of severe visual loss

• Choroidal neovascularisation (CNV): new vessels from choriocapillaris breach Bruch's membrane into sub-RPE/subretinal space
• Rapid, distorted, central visual loss
• Metamorphopsia (distortion) tested with Amsler grid
• Disciform scar (end stage)

• Ranibizumab (Lucentis) — Fab fragment of anti-VEGF-A antibody
• Bevacizumab (Avastin) — full antibody, off-label
• Aflibercept (Eylea) — VEGF trap, binds VEGF-A, VEGF-B, PlGF
• Brolucizumab (Beovu) — newer, single-chain antibody fragment
• Photodynamic therapy (PDT) with verteporfin — for subfoveal classic CNV (now less used)

• Hard drusen (<63 μm): small, discrete — low risk
• Soft drusen (≥63 μm): large, confluent — high risk of progressing to geographic atrophy or CNV
• Drusen are the hallmark of early dry ARMD

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8. Retinitis Pigmentosa (RP)

• Nyctalopia (night blindness) — earliest symptom
• Progressive peripheral visual field loss → tunnel vision
• Eventual central vision loss (late)

• Bone-spicule pigmentation in the midperipheral retina (pathognomonic-like)
• Attenuated/thread-like retinal arterioles
• Waxy pallor of optic disc
• Vitreous cells (fine)
• Cystoid macular oedema (CMO) common cause of central visual loss

• Electroretinogram (ERG) — extinguished or severely reduced rod and cone responses (gold standard for diagnosis)
• Visual field (Goldmann perimetry) — ring scotoma progressing to tunnel vision
• Dark adaptation testing
• Genetic testing (>70 genes implicated: RHO, RPGR, RP2, PRPF31, etc.)
• OCT — CMO, outer nuclear layer thinning

• Autosomal dominant (AD) — most common, milder
• Autosomal recessive (AR) — more severe, earlier onset (commonest overall)
• X-linked recessive (XL) — most severe, onset in first decade
• Digenic, mitochondrial

• Usher syndrome: RP + sensorineural hearing loss (most common RP syndrome)
• Bardet-Biedl syndrome: RP + obesity + polydactyly + intellectual disability + renal anomalies
• Refsum disease: RP + peripheral neuropathy + cerebellar ataxia + ichthyosis (phytanic acid accumulation)
• Kearns-Sayre syndrome (mitochondrial): RP + CPEO + cardiac conduction defects
• Lawrence-Moon syndrome: RP + spastic paraplegia + intellectual disability + hypogonadism (no polydactyly)
• Abetalipoproteinaemia (Bassen-Kornzweig): RP + ataxia + acanthocytosis + fat malabsorption

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9. Retinal Detachment (RD)

• Photopsia (flashes of light) — traction on retina stimulates rods
• Floaters (sudden increase) — vitreous haemorrhage or pigment cells (Shafer's sign = tobacco dust in vitreous = retinal break)
• Visual field defect — typically a "curtain" or "shadow" from periphery
• Reduced VA — if macula detached ("macula-off")

• Sharply demarcated oval/circumferential areas of retinal thinning in the equatorial zone
• White lattice-work lines (sclerosed vessels)
• Atrophic round holes within the lesion
• Vitreous liquefied within lesion, condensed at edges
• Risk factor for rhegmatogenous RD, especially in high myopes

• Prophylactic: Laser photocoagulation or cryotherapy around breaks
• Scleral buckle: Indent sclera to bring choroid into contact with retina, relieving vitreous traction
• Pars plana vitrectomy (PPV) with gas/silicone oil tamponade — for posterior breaks, giant tears, complex detachments
• Pneumatic retinopexy: Intravitreal gas bubble + laser/cryo — for suitable superior breaks

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10. Other Retinal Conditions

• Accumulation of serous fluid under the neurosensory retina (subretinal fluid), detaching it from the RPE
• Predominantly young-to-middle-aged men, type A personality
• Associated with: corticosteroid use, Cushing syndrome, stress, H. pylori
• Symptoms: unilateral blurring, micropsia, metamorphopsia
• Diagnosis: OCT (neurosensory detachment), FA (leaking point — "smokestack" or "ink-blot" pattern)
• Treatment: most resolve spontaneously in 3 months; persistent cases treated with photodynamic therapy (half-dose PDT) or micropulse laser

• Stage 1: Impending (foveal detachment/pseudocyst)
• Stage 2: Small (<400 μm) full-thickness
• Stage 3: ≥400 μm full-thickness, no posterior vitreous detachment
• Stage 4: Full-thickness + posterior vitreous separation Treatment: PPV + internal limiting membrane (ILM) peeling + gas tamponade (C3F8 or SF6); face-down positioning post-op.

• Pathophysiology: Premature exposure to high O2 → cessation of vascular development → relative ischaemia → VEGF-driven neovascularisation
• Zones (I, II, III — concentric around disc), Stages (1–5)
• Rush disease / Plus disease: vessel dilatation and tortuosity = severe
• Treatment: laser photocoagulation of avascular retina, intravitreal anti-VEGF (bevacizumab), vitreoretinal surgery for advanced stage

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PART C: NEURO-OPHTHALMOLOGY

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11. Visual Pathway & Field Defects

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12. Pupil Abnormalities

• React to accommodation but NOT to light ("prostitute's pupil" — accommodates but doesn't react)
• Bilateral (usually asymmetric)
• Classic cause: Neurosyphilis (tabes dorsalis, GPI)
• Lesion: pretectal nucleus in midbrain (dissociation between light and accommodation pathways)
• Poorly dilate with mydriatics

• Unilateral dilated pupil with poor/absent light reflex and slow, tonic near response (accommodates slowly and redilates slowly)
• Caused by: post-ganglionic parasympathetic denervation (ciliary ganglion damage — often post-viral, autoimmune)
• Supersensitive to dilute pilocarpine (0.1%) — will constrict (denervation supersensitivity)
• Holmes-Adie syndrome = Adie pupil + absent deep tendon reflexes (predominantly in young women)

1. Ptosis (partial — superior tarsal muscle/Müller's muscle)
2. Miosis (small pupil — dilator pupillae affected)
3. Anhidrosis (depending on level)
4. Enophthalmos (apparent, not true), lower lid elevation (upside-down ptosis)

• Central (1st order — hypothalamus to ciliospinal centre of Budge at C8-T2): stroke, MS, syringomyelia, Wallenberg syndrome (lateral medullary)
• Pre-ganglionic (2nd order — exit at T1 to superior cervical ganglion): Pancoast tumour (apex of lung), cervical rib, thyroidectomy, carotid endarterectomy, brachial plexus injury
• Post-ganglionic (3rd order — superior cervical ganglion onward): carotid artery dissection, cavernous sinus lesion, cluster headache, middle ear pathology

• 0.5–1% apraclonidine (alpha-2 agonist): both dilate in normal; in Horner's, the affected pupil dilates more (due to denervation supersensitivity) — reverses the anisocoria. Confirms Horner's.
• Cocaine (4–10%) test: blocks reuptake of noradrenaline; normal pupil dilates; Horner's pupil fails to dilate (regardless of level). Confirms Horner's.
• 1% hydroxyamphetamine (paredrine): releases stored noradrenaline from 3rd order neuron endings. Dilates in central/preganglionic (1st and 2nd order); fails to dilate in postganglionic Horner's.

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13. Optic Nerve

• Blurred disc margins (begins nasal side)
• Loss of spontaneous venous pulsations (SVP) — early sign
• Venous dilatation
• Flame-shaped haemorrhages
• Cotton-wool spots
• Optociliary shunt vessels (chronic)
• VA initially preserved; transient visual obscurations on postural change; enlarged blind spot

• Demyelinating (most common): associated with Multiple Sclerosis (MS); 50–70% develop MS within 15 years (ONTT data)
• Symptoms: subacute monocular visual loss over hours to days, pain on eye movement (92%), reduced colour vision (red desaturation), central scotoma, RAPD
• MRI: T2/FLAIR periventricular white matter lesions → indicates high risk of MS (McDonald criteria)
• VEP: delayed P100 latency (even after recovery — demyelination leaves residual slowing)
• Treatment: IV methylprednisolone 1g/day × 3 days accelerates recovery but does not improve final visual outcome (ONTT)

• Symptoms: headache (temporal), scalp tenderness, jaw claudication, constitutional symptoms, polymyalgia rheumatica (PMR)
• Eye: AAION (most common), CRAO, diplopia (CROME)
• ESR >50 mm/hr, CRP elevated, thrombocytosis
• Treatment: Immediate IV methylprednisolone if ocular involvement, then oral prednisolone. Biopsy confirms but should not delay treatment.

• Sequential (rarely simultaneous) loss of central vision in both eyes
• Cecocentral scotoma
• Disc appears hyperaemic and pseudoedematous early, then atrophy
• No pain
• Most have poor visual prognosis (G11778A worst); T14484C has best recovery rate
• Idebenone (antioxidant) — only licensed treatment, modest benefit

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14. Ocular Motor Nerves

• Motor nucleus in midbrain at level of superior colliculus
• Edinger-Westphal nucleus (pupilloconstrictor fibres lie on the outside/periphery of the nerve)
• Runs in subarachnoid space between PCA and SCA
• Passes through cavernous sinus (lateral wall, above CN IV)
• Enters orbit via superior orbital fissure
• Supplies: SR, MR, IR, IO (extraocular muscles), levator palpebrae; pupillary sphincter

• Ptosis (complete — levator palpebrae)
• Eye deviation: "down and out" (unopposed SO and LR)
• Mydriasis: dilated fixed pupil (if compressive) — pupil-involving
• Diplopia
• Loss of accommodation

• Pupil-involving (fixed dilated) CN III palsy: compressive lesion (posterior communicating artery aneurysm, uncal herniation) — neurosurgical emergency. Parasympathetic fibres run on the outside of CN III and are compressed first.
• Pupil-sparing CN III palsy: microvascular ischaemia (diabetes, hypertension) — inner fibres affected first; parasympathetic fibres spared.
• Rule: Any painful or pupil-involving CN III palsy → urgent MRI/MRA for PComm aneurysm.

• Longest intracranial course; crosses in the dorsal midbrain (only CN that exits dorsally)
• Supplies: Superior oblique (SO) — depression in adduction, intorsion
• Features: Vertical diplopia (worse on down-gaze, e.g., reading/stairs), head tilt away from affected side (to reduce torsional diplopia)
• Bielschowsky head tilt test: tilting head to affected side worsens diplopia
• Most common isolated CN palsy from closed head trauma; also congenital

• Supplies: Lateral rectus (LR) — abduction
• Features: Esotropia (convergent squint), horizontal diplopia (worse on ipsilateral gaze, at distance), face turn toward affected side
• Long intracranial course → common non-localising sign of raised ICP
• Causes: Gradenigo syndrome (apex petrositis — CN VI + CN V + ipsilateral ear pain), pontine lesion, meningitis, nasopharyngeal carcinoma, raised ICP

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15. Other Neuro-ophthalmology Topics

• Features: Impaired adduction of ipsilateral eye (on contralateral gaze) + nystagmus of abducting eye
• Bilateral INO in young person → MS (most common cause)
• Unilateral INO in elderly → vascular (stroke)
• Convergence is preserved (distinguishes from MR palsy)
• WEBINO (Wall-Eyed Bilateral INO) = bilateral INO + exotropia at rest

• One eye cannot move horizontally at all (the "one")
• Contralateral eye can only abduct ("half")
• Only movement preserved: abduction of the contralateral eye
• Cause: pontine stroke, MS, glioma

• Jerk nystagmus: slow phase (drift) + fast corrective phase (named by direction of fast phase)
• Pendular nystagmus: equal velocity in both directions

• Convergence retraction nystagmus (on attempted upgaze)
• Accommodation-convergence (loss)
• Gaze palsy (bilateral upgaze paralysis — most characteristic)
• Edlinger-Westphal: light-near dissociation of pupils (pupils react to near, not light)
• Cause: pineal gland tumour (especially adolescents), hydrocephalus, dorsal midbrain stroke/haemorrhage
• Collier's sign: bilateral lid retraction

• Raised ICP without hydrocephalus or mass lesion
• CSF composition normal, but opening pressure >25 cmH₂O
• Demographics: obese young women
• Associations: tetracyclines, vitamin A excess/toxicity, steroids withdrawal, OCP, isotretinoin
• Symptoms: headache (worse on coughing/bending), transient visual obscurations, diplopia (CN VI palsy), pulsatile tinnitus
• Exam: bilateral papilloedema, enlarged blind spot
• Treatment: weight loss, acetazolamide (carbonic anhydrase inhibitor), topiramate; optic nerve sheath fenestration (for visual loss); LP shunting; venous sinus stenting

• Primary optic atrophy: White, flat disc with sharp margins; no preceding disc oedema. Causes: optic neuritis, AION, optic nerve compression, toxic (methanol, tobacco), hereditary (LHON, Kjer disease).
• Secondary optic atrophy: Dirty grey disc, indistinct margins; follows papilloedema.
• Consecutive (ascending) atrophy: follows retinal disease (e.g., RP, widespread retinal degeneration).

• Ipsilateral optic atrophy (direct compression of ipsilateral optic nerve)
• Contralateral papilloedema (raised ICP from mass)
• Anosmia (olfactory nerve involvement) Classic cause: Olfactory groove meningioma (or frontal lobe tumour) Pseudo-Foster-Kennedy: asymmetric sequential AION (bilateral AION, not a mass)

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16. Drugs in Ophthalmology / Drug-Induced Retinal Toxicity

• Hydroxychloroquine/Chloroquine → Bull's eye maculopathy (pericentral > central ring of RPE atrophy); screening with OCT + mfERG; hydroxychloroquine safe dose <5 mg/kg/day
• Thioridazine (phenothiazine) → pigmentary retinopathy, night blindness
• Vigabatrin → irreversible concentric visual field constriction
• Quinine → acute retinal toxicity (high doses), arteriolar spasm, optic atrophy
• Tamoxifen → crystalline maculopathy (white refractile deposits in inner retina)
• Ethambutol → optic neuritis (red-green colour vision loss, central scotoma)
• Methanol → optic atrophy

• Posterior subcapsular cataract (PSC) — dose and duration dependent
• Raised IOP → steroid-induced glaucoma (open-angle)
• Susceptibility to infections (herpes simplex keratitis recurrence)
• IIH (benign intracranial hypertension) on withdrawal
• Central serous chorioretinopathy

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17. Electrodiagnostic Tests

• a-wave (negative): photoreceptor response
• b-wave (positive): bipolar cell + Müller cell response
• Dark-adapted (scotopic) ERG tests rod function
• Light-adapted (photopic) ERG tests cone function
• ERG extinguished in RP; reduced a-wave in severe photoreceptor disease
• Normal ERG but abnormal VEP → optic nerve disease

• Delayed P100 latency: optic neuritis, demyelination (MS) — hallmark
• Reduced P100 amplitude: optic atrophy, severe retinal disease
• Pattern VEP (alternating checkerboard) is most sensitive
• Used in: MS diagnosis, optic nerve function in pre-verbal children, functional visual loss

• Subnormal in: Best's vitelliform macular dystrophy (low Arden ratio with normal ERG — pathognomonic), chloroquine toxicity

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18. Important Clinical Signs & Mnemonics

• Raised ICP (brain tumour, hydrocephalus, idiopathic IIH)
• Optic neuritis / neuroretinitis (Bartonella, viral)
• Hypertensive retinopathy
• Pseudopapilloedema (drusen of the optic nerve head — bright on B-scan US)
• Leber hereditary optic neuropathy (pseudoedema in early phase)

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19. Rapid-Fire One-Liners (MBBS MCQ Favourites)

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