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AN41.1-3 | Eyeball — Gate Quiz
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The three coats of the eyeball from outer to inner are:
Correct! The three coats of the eyeball from outer to inner are: (1) Outer fibrous coat: sclera (posterior 5/6) + cornea (anterior 1/6); (2) Middle vascular coat (uvea): choroid + ciliary body + iris; (3) Inner neural coat: retina.
Eyeball coats (outer to inner): 1. Fibrous = Sclera (opaque, posterior 5/6) + Cornea (transparent, anterior 1/6). 2. Uvea/vascular = Choroid (nourishes retina) + Ciliary body (secretes aqueous, accommodation) + Iris (pupil control). 3. Retina = RPE + photoreceptors + bipolar + ganglion cells.
Incorrect. Three coats outer→inner: Fibrous (sclera + cornea) → Vascular/Uvea (choroid + ciliary body + iris) → Neural (retina).
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Aqueous humour is produced by the ciliary processes and follows a specific path. Which sequence is correct?
Correct! The complete pathway: Ciliary processes (production) → posterior chamber → through the pupil → anterior chamber → trabecular meshwork at the iridocorneal angle → Canal of Schlemm → aqueous veins → episcleral veins → venous system.
Aqueous humour circuit: Produced by ciliary body processes → posterior chamber → through pupil → anterior chamber → drainage at iridocorneal angle → trabecular meshwork → Canal of Schlemm (venous sinus at limbus) → aqueous veins → episcleral veins. In glaucoma, outflow is impaired (usually at trabecular meshwork in open-angle type).
Incorrect. Correct sequence: Ciliary processes → posterior chamber → THROUGH THE PUPIL → anterior chamber → trabecular meshwork → Canal of Schlemm → aqueous veins.
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In chronic open-angle glaucoma, progressive optic nerve damage occurs at the lamina cribrosa. The lamina cribrosa is located in:
Correct! The lamina cribrosa is a sieve-like perforated area of the sclera through which the retinal nerve fibres pass to form the optic nerve. It is the mechanically weakest part of the sclera and the site where raised intraocular pressure causes compressive damage to optic nerve axons in glaucoma.
Lamina cribrosa = sieve-like area of sclera at the optic disc. Retinal nerve fibres pass through its pores. In glaucoma, elevated IOP compresses these fibres here (the weakest scleral point) → progressive axonal death → optic disc cupping (increased cup-to-disc ratio). Fundoscopy: cup-to-disc ratio >0.6 is suspicious; asymmetry >0.2 between eyes is abnormal.
Incorrect. The lamina cribrosa is in the SCLERA at the optic disc — the area where the optic nerve pierces the sclera. The sieve-like holes allow retinal nerve fibres to pass through, and this is where glaucomatous cupping occurs.
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In phacoemulsification cataract surgery, the surgeon opens the anterior lens capsule using a continuous curvilinear capsulotomy. After emulsifying and removing the nuclear lens material, the intraocular lens is implanted inside the residual lens capsule. The lens derives nutrition from:
Correct! The lens is avascular — it has no blood vessels or nerves. It derives all its nutrition via diffusion from the aqueous humour surrounding it (anterior and posterior chambers). When aqueous humour composition changes (e.g., in diabetes, abnormal glucose levels) or with aging, lens fibre metabolism is impaired and proteins aggregate → cataract.
Lens facts: Avascular + aneural. Nutrition = aqueous humour diffusion only. Composed of: capsule (basement membrane) + anterior epithelium + lens fibres (no nuclei, elongated). Cataract = lens opacity. Types: Nuclear (aging, index myopia), Cortical (spoke-like opacities), Posterior subcapsular (steroids, diabetes). Treatment: phacoemulsification + IOL implantation.
Incorrect. The lens is avascular and AVASCULAR. It receives nutrition exclusively by diffusion from aqueous humour. This is why conditions that alter aqueous composition (diabetes, galactosaemia) promote cataract formation.
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In central retinal artery occlusion (CRAO), fundoscopy classically shows a pale, milky-white retina with a cherry-red spot at the macula. The cherry-red spot appears because:
Correct! The fovea centralis at the centre of the macula is very thin (the inner retinal layers are displaced laterally in this region to allow direct light access to photoreceptors). In CRAO, the inner retinal layers become oedematous and white due to infarction, but at the fovea, the choroidal circulation (which is intact) shows through the thin retina as a red spot — contrasting against the surrounding white infarction.
CRAO fundoscopy: Pale/milky retina (inner layer infarction) + cherry-red spot at fovea (thin retina → intact choroid visible). CRA is a functional end-artery. Outer retinal layers (photoreceptors) survive (choroidal supply). Inner layers (bipolar + ganglion cells) die. Emergency: restore flow within 90 minutes. Cause: embolism (carotid plaques, cardiac), thrombosis, giant cell arteritis.
Incorrect. The cherry-red spot occurs because: (1) the fovea is THIN (inner layers displaced), (2) the CHOROIDAL circulation is intact (CRAO only occludes the central retinal artery, not choroidal vessels), and (3) the choroidal red colour shows through the thin fovea against the white infarcted retina.
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The sphincter pupillae is innervated by parasympathetic fibres that synapse in the ciliary ganglion. The preganglionic fibres reach the ciliary ganglion via:
Correct! The preganglionic parasympathetic fibres travel in the oculomotor nerve (CN III) from the Edinger-Westphal nucleus in the midbrain to the ciliary ganglion in the orbit. They synapse there, and postganglionic fibres travel via the short ciliary nerves to reach the sphincter pupillae (constriction) and ciliary muscle (accommodation).
Pupillary constriction pathway: Edinger-Westphal nucleus → CN III (oculomotor) → ciliary ganglion (synapse) → short ciliary nerves → sphincter pupillae + ciliary muscle. CN III palsy → loss of pupillary constriction → fixed dilated pupil. Parasympathetic fibres run on the OUTSIDE of CN III — herniation (uncal herniation) compresses them first → blown (dilated) pupil as early sign.
Incorrect. Preganglionic parasympathetic → CN III → ciliary ganglion. Postganglionic → short ciliary nerves → sphincter pupillae + ciliary muscle. Long ciliary nerves carry sympathetic fibres (from superior cervical ganglion) to dilator pupillae.
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During near vision (accommodation), the ciliary muscle contracts. The immediate consequence of this contraction on the zonular fibres and the lens is:
Correct! When the ciliary muscle contracts (for near vision), the ciliary body moves inward → reducing tension on the zonular fibres → they RELAX → the elastic lens springs back to its naturally more CONVEX shape → increased refractive power for near vision.
Accommodation (near vision): Ciliary muscle contracts → ciliary ring shortens → zonular fibres relax → lens becomes more convex (higher power). Far vision: Ciliary muscle relaxes → zonular fibres taut → lens flattens (lower power). Atropine (cycloplegic): paralyses ciliary muscle + sphincter pupillae → loss of accommodation + pupil dilation. Used for fundoscopy and refraction.
Incorrect. Ciliary muscle contraction → ciliary body moves inward → zonular fibres RELAX (become slack) → lens becomes more CONVEX (elastic recoil) → higher refractive power = near vision. This is counterintuitive: muscle contraction = lens becomes more convex by releasing tension.
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A patient presents with a constricted right pupil (miosis), mild drooping of the right upper eyelid (partial ptosis), and absence of sweating on the right side of the face. The sympathetic supply to the right eye is interrupted. This is consistent with:
Correct! Horner's syndrome = interruption of the sympathetic supply to the eye. Signs: (1) Miosis (dilator pupillae paralysed), (2) Partial ptosis (Müller's muscle in upper lid is sympathetically innervated), (3) Anhidrosis of the face (if the lesion is below the superior cervical ganglion), (4) Apparent enophthalmos (lower lid elevation). The pupil is small (miosis) — opposite to CN III palsy (which causes a dilated pupil).
Horner's syndrome signs: Miosis (small pupil — dilator pupillae paralysed) + Partial ptosis (Müller's muscle denervated) + Anhidrosis (face sweating fibres). Causes: Central (hypothalamus→spinal cord: demyelination, stroke), Preganglionic (Pancoast tumour, cervical rib, thyroid carcinoma), Postganglionic (carotid dissection, cavernous sinus lesion). Compare: CN III palsy = LARGE fixed dilated pupil + complete ptosis + "down and out" eye.
Incorrect. Horner's syndrome = sympathetic interruption → miosis + partial ptosis + anhidrosis. CN III palsy = parasympathetic loss → DILATED (large) pupil + complete ptosis + eye looking "down and out".
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The fovea centralis, the area of highest visual acuity in the retina, has which structural characteristic that accounts for its acuity?
Correct! The fovea centralis has: (1) Only cones (no rods) — cones provide colour and high-acuity vision, (2) Inner retinal layers (ganglion cells, bipolar cells) are displaced laterally in the foveal pit (foveal depression) so light falls DIRECTLY on the photoreceptors without being scattered, (3) This creates the foveal avascular zone (no blood vessels to scatter light). These features maximise visual acuity.
Fovea centralis: All cones (no rods) + inner retinal layers displaced → direct light path + no blood vessels (foveal avascular zone). Maximum visual acuity here. Used for reading and detailed vision. Macula = the broader pigmented region around the fovea (yellow appearance due to xanthophyll pigment — macular pigment). Damaged in age-related macular degeneration, diabetic maculopathy.
Incorrect. Fovea = only CONES (no rods), inner layers displaced (direct photon access), no blood vessels (foveal avascular zone). Rods are for dim/scotopic vision; the fovea is the cone-rich high-acuity zone.
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A 65-year-old hypermetropic (far-sighted) woman presents at night with severe unilateral eye pain, headache, nausea, and blurred vision with haloes around lights. Examination shows a red eye, semi-dilated non-reactive pupil, and rock-hard eyeball. The most likely diagnosis and its anatomical basis are:
Correct! This is acute angle-closure glaucoma. The iridocorneal angle (trabecular meshwork) is suddenly occluded by the iris (pupillary block → iris pushed forward) → aqueous drainage is completely blocked → IOP shoots up to 50-70 mmHg → severe eye pain, headache, nausea, coloured haloes (corneal oedema diffracts light), rock-hard eyeball. Hypermetropic eyes are anatomically predisposed (shallower anterior chamber, narrower angle). Occurs at night when pupil is semi-dilated (dim light).
Acute angle-closure glaucoma: Shallow anterior chamber + narrow iridocorneal angle (hypermetropes) + pupil semi-dilation (dim light, mydriatic drops) → iris bunches up at the angle → outflow blocked → IOP 50-70 mmHg. Emergency signs: severe pain, nausea, haloes, semi-dilated fixed pupil, red eye, rock-hard eye. Treatment: IV acetazolamide + IV mannitol + topical pilocarpine + emergency laser peripheral iridotomy.
Incorrect. The clinical triad of sudden severe eye pain + haloes + rock-hard eye at night in a hypermetropic patient = acute angle-closure glaucoma. Treatment: IV acetazolamide + topical pilocarpine + mannitol IV → emergency laser iridotomy.
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