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OP9.1-5 | Retina, Optic Nerve and Visual Pathway — Practice Quiz
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A medical student performs direct ophthalmoscopy and sets the diopter wheel to +10 before approaching the patient. At what distance from the patient's eye will he obtain a focused view of the fundus?
Correct. The relationship is: working distance (cm) = 100 / diopter power. +10 D gives a 10 cm working distance. This setting is used for the anterior segment, not the fundus.
Each diopter on the direct ophthalmoscope corresponds to approximately 1 cm of working distance (100/diopters). A +10 diopter setting focuses at 10 cm — useful for examining the anterior segment, not the fundus. To examine the fundus, a low or zero diopter setting is used and the examiner must be close to the patient's eye.
Recall that each diopter corresponds to approximately 1 cm of working distance (100/diopters). +10 D therefore focuses at 10 cm, useful for examining the anterior structures. For fundus examination, a low diopter setting and close approach are needed.
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On fundoscopy of a 45-year-old man with 10-year history of type 2 diabetes, you find microaneurysms, dot-and-blot haemorrhages, and hard exudates within the temporal arcades but no new vessels on or near the disc. Macular OCT shows central subfield thickness of 380 micrometres with hard exudates threatening the fovea. How should this patient be managed?
Correct. Centre-involving DMO is the first-line indication for intravitreal anti-VEGF therapy. There is no indication for PRP here because there is no proliferative disease. Focal laser may be considered for non-centre-involving CSME.
This patient has moderate NPDR with clinically significant macular oedema (CSME) involving the centre. First-line treatment for centre-involving diabetic macular oedema is intravitreal anti-VEGF (e.g., ranibizumab, aflibercept). PRP is indicated for PDR or severe NPDR, not for macular oedema. Vitrectomy is for non-clearing vitreous haemorrhage or tractional detachment.
The fundus shows NPDR features (microaneurysms, dot-blot haemorrhages, hard exudates) — no new vessels — so this is not PDR and PRP is not indicated. The OCT confirms centre-involving diabetic macular oedema, which requires intravitreal anti-VEGF as first-line treatment. Observation is inappropriate when the fovea is threatened.
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Which of the following fundoscopic findings is the hallmark of proliferative diabetic retinopathy that distinguishes it from severe non-proliferative diabetic retinopathy?
Correct. Neovascularisation — new vessels on the disc (NVD) or elsewhere (NVE) — is the defining hallmark of PDR. All other findings listed are features of severe NPDR.
The defining feature of PDR is neovascularisation — new vessel formation on the disc (NVD) or elsewhere on the retina (NVE). Venous beading, IRMA, and extensive haemorrhages are features of severe NPDR (4-2-1 rule) but without new vessels. Once new vessels appear, the classification changes to PDR regardless of other findings.
Venous beading, IRMA, and extensive haemorrhages fulfil the 4-2-1 criteria for severe NPDR but are still within the NPDR category. The critical threshold to PDR is crossed when new vessels appear (NVD or NVE). NPDR changes remain within existing vessels; PDR involves growth of new, fragile vessels outside existing vascular walls.
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A 65-year-old man with atrial fibrillation presents with sudden painless complete loss of vision in his right eye for 90 minutes. Fundoscopy shows diffuse retinal whitening with a cherry-red spot at the fovea. The RAPD is present on the right. What is the most appropriate immediate management?
Correct. CRAO is treated with measures to lower IOP (ocular massage, acetazolamide) to allow perfusion of the retinal circulation and dislodge the embolus. This is a time-critical emergency analogous to acute MI.
This is central retinal artery occlusion (CRAO) — an ocular emergency. The cherry-red spot occurs because the foveal choroidal circulation (visible through the thin foveal retina) remains intact while the surrounding ischaemic retina is opacified. Immediate management includes digital ocular massage (to dislodge embolus), IV acetazolamide or anterior chamber paracentesis (to lower IOP), and urgent ophthalmology referral. The window for potential recovery is within 90-120 minutes.
The cherry-red spot with diffuse retinal whitening and sudden painless monocular visual loss is the classic presentation of CRAO — an ocular emergency. Anti-VEGF and laser are not acute interventions for arterial occlusion. Corticosteroids are used for giant cell arteritis-associated CRAO. The acute management targets IOP reduction and embolus dislodgement.
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A 58-year-old woman with hypertension and hypercholesterolaemia presents with sudden painless blurring of vision in her left eye over 2 days. Fundoscopy shows flame-shaped haemorrhages in all four quadrants, dilated tortuous veins, disc oedema, and multiple cotton-wool spots. Visual acuity is 6/60. What is the most likely diagnosis?
Correct. The blood-and-thunder fundus (haemorrhages in all four quadrants, engorged tortuous veins, disc swelling) is the hallmark of CRVO — sometimes described as a fundus that looks like a stormy sunset.
The blood-and-thunder fundus — flame haemorrhages in all four quadrants, dilated tortuous veins, disc oedema, and cotton-wool spots — is the classic appearance of CRVO. Contrast with CRAO: the artery is paler, has a cherry-red spot, and no haemorrhages. PDR shows new vessels. Hypertensive retinopathy with papilloedema is bilateral. CRVO is typically unilateral.
CRAO produces diffuse retinal whitening with a cherry-red spot, not haemorrhages. PDR shows new vessels, not the four-quadrant haemorrhagic picture. Hypertensive retinopathy grade IV is bilateral. The four-quadrant flame haemorrhages with engorged veins and disc oedema in a single eye point to CRVO.
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A 2-year-old child is brought to the paediatric clinic because the mother noticed a white reflex in the child's right eye in a flash photograph. There is no squint and the child appears otherwise well. What is the most critical next step?
Correct. Leukocoria = ophthalmology referral on the same day. No delay is acceptable. Retinoblastoma is curable if detected early but fatal if missed.
Leukocoria (white pupil) in a child must be treated as retinoblastoma until proven otherwise. Retinoblastoma is the most common primary intraocular malignancy in children and is life-threatening if not diagnosed early. The correct action is same-day ophthalmology referral — not reassurance, not glasses, and not delaying for an MRI ordered from primary care. The ophthalmologist will perform dilated fundoscopy under anaesthesia and arrange imaging.
A white pupil reflex (leukocoria) in a young child is a red-flag sign that demands immediate same-day ophthalmology referral. Retinoblastoma must be excluded — it is a life-threatening malignancy. Reassurance or watchful waiting is never appropriate. The ophthalmologist will arrange examination under anaesthesia and imaging, not the primary care physician.
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A 70-year-old man with AMD presents with sudden onset of central scotoma and metamorphopsia (distortion of straight lines) in his right eye. He previously had dry AMD. Fundoscopy now shows a greyish-green subretinal lesion with surrounding haemorrhage at the macula. What is the most likely new complication and its first-line treatment?
Correct. Metamorphopsia with a subretinal neovascular membrane signals wet AMD (choroidal neovascularisation). Anti-VEGF injections are the standard first-line treatment and have transformed the prognosis of wet AMD.
Sudden onset metamorphopsia with a subretinal neovascular membrane and haemorrhage represents conversion from dry AMD to wet (neovascular) AMD due to choroidal neovascularisation (CNV). First-line treatment is intravitreal anti-VEGF (ranibizumab, aflibercept, or bevacizumab). Photodynamic therapy with verteporfin is an alternative for predominantly classic CNV.
Geographic atrophy is the end-stage of dry AMD — it does not present acutely with metamorphopsia and haemorrhage. CSR typically affects younger men (age 30-50) and presents with a serous detachment, not a subretinal membrane. The clinical picture — known dry AMD, sudden metamorphopsia, subretinal grey-green lesion with haemorrhage — points to wet AMD (CNV), treated with intravitreal anti-VEGF.
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On Humphrey visual field testing, a patient is found to have loss of the right half of the visual field in both eyes (right homonymous hemianopia). Where is the responsible lesion?
Correct. Right homonymous hemianopia = left-sided post-chiasmal lesion (left optic tract, radiation, or cortex). The rule: the lesion is always contralateral to the side of field loss.
A homonymous hemianopia (same-side field loss in both eyes) indicates a post-chiasmal lesion. Because the right visual field is processed by the left hemisphere (fibres from both eyes cross at the chiasm so that the left optic tract carries the right visual field), a right homonymous hemianopia localises to the left optic tract, left optic radiation, or left occipital cortex.
A monocular field defect = optic nerve lesion. A bitemporal hemianopia = chiasmal lesion. A homonymous hemianopia (same-side loss in both eyes) = post-chiasmal lesion on the OPPOSITE side. The right visual field is represented in the left hemisphere. Therefore, right homonymous hemianopia localises to the left optic tract or visual pathway.
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A 28-year-old woman presents with painful visual loss in her right eye over 4 days. Visual acuity is 6/60 right, 6/6 left. There is a right RAPD. Colour vision is severely impaired in the right eye. Fundoscopy shows a swollen right optic disc. MRI brain reveals a demyelinating plaque in the right optic nerve. What is the most likely diagnosis?
Correct. Optic neuritis — painful visual loss, RAPD, colour vision loss, disc swelling in a young woman with demyelinating plaque on MRI — is a classic presentation and may herald multiple sclerosis.
Optic neuritis classically presents as painful visual loss in a young adult (especially female), with RAPD, impaired colour vision (red desaturation), and a swollen disc (in anterior optic neuritis) or normal disc (retrobulbar neuritis). It is strongly associated with multiple sclerosis. AION presents in older patients with vascular risk factors and is typically painless. Papilloedema is bilateral and preserves acuity until late.
Papilloedema is bilateral and does not cause significant acuity loss early. AION is typically painless and occurs in older patients with vascular risk factors. CRVO causes haemorrhages and engorged veins, not disc swelling alone with pain and RAPD. The combination of pain, RAPD, colour vision loss, monocular disc swelling, and demyelination on MRI defines optic neuritis.
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The cup-to-disc ratio (CDR) is assessed during routine fundoscopy. Which of the following is considered the upper limit of normal for the vertical CDR?
Correct. CDR up to 0.5 is normal. A CDR >0.5 or inter-eye asymmetry >0.2 should raise concern for glaucoma.
The normal cup-to-disc ratio is up to 0.5. A CDR above 0.5, asymmetry of more than 0.2 between the two eyes, or notching of the neuroretinal rim raises suspicion for glaucomatous optic neuropathy. In practice, it is the combination of CDR, rim tissue appearance, and visual field defects that establishes the diagnosis.
The normal cup-to-disc ratio is considered up to 0.5 (vertical). Values above 0.5 or asymmetry between the two eyes of more than 0.2 warrant further evaluation for glaucoma. A CDR of 0.7 would be distinctly suspicious.
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