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OP1.1-5 | Visual Foundations and Refraction — Graded Quiz
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A 35-year-old woman presents with a two-week history of central vision loss in her right eye with a central scotoma. Visual acuity is 6/36 in the right eye and 6/6 in the left. The pinhole does NOT improve her right eye vision. Colour vision is reduced in the right eye (she sees 5/17 Ishihara plates compared to 17/17 in the left). Which is the most appropriate next clinical step?
Correct. The pinhole failure rules out a refractive cause. Dyschromatopsia + central scotoma in a young adult is the classic presentation of optic neuritis requiring urgent neurological and ophthalmological evaluation.
The pinhole does NOT improve vision, ruling out a refractive cause. Reduced colour vision (dyschromatopsia) combined with a central scotoma in a young adult strongly suggests optic nerve pathology (optic neuritis is common in this demographic). This is an urgent referral — the 'no refraction, no rest' rule: if pinhole fails to improve VA, organic disease must be sought.
Pinhole failure + dyschromatopsia + central scotoma = organic (neural) cause, not refractive. New spectacles will not help. Urgent referral for optic nerve/neurological investigation is required.
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A right homonymous hemianopia (loss of the right half of both visual fields) is found on formal perimetry. Where is the lesion most likely located?
Correct. Retrochiasmal lesions (optic tract, radiation, cortex) produce homonymous defects ipsilateral to the field loss but contralateral to the lesion. Right homonymous hemianopia = left-sided retrochiasmal lesion.
After the chiasma, each visual pathway carries information exclusively from the contralateral visual field. A right homonymous hemianopia (loss of the right visual field in both eyes) means the left visual pathway (left optic tract, left optic radiation, or left visual cortex) is damaged — contralateral to the field defect.
Right homonymous hemianopia localises to the left retrochiasmal pathway. After the chiasma, each pathway carries the contralateral visual field; the right visual field is processed by the left hemisphere.
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A 10-year-old boy is found to have VA 6/6 OD and 6/60 OS. The left eye VA does not improve with a pinhole. Anterior segment and fundus are normal bilaterally. Cover test reveals a manifest left esotropia. What type of amblyopia does this child most likely have, and what is the primary treatment approach?
Correct. Manifest esotropia causes strabismic amblyopia via cortical suppression of the deviating eye. Treatment: full optical correction first, then patching of the dominant (right) eye. Bilateral patching is never correct for unilateral amblyopia.
Manifest esotropia (squint) + unilateral VA loss not explained by structural pathology = strabismic amblyopia. The brain suppresses the deviated eye's image. First-line treatment: correct any refractive error with spectacles, then occlude (patch) the dominant eye to force fixation through the amblyopic eye during the critical period.
The esotropia identifies this as strabismic amblyopia. Deprivation requires a physical obstruction (cataract, ptosis); ametropic requires bilateral high refractive error. Treatment is optical correction + dominant-eye patching.
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A 30-year-old pilot with −7.00 D myopia requests laser refractive surgery to be free of spectacles. Corneal topography shows normal curvature. Corneal thickness is 480 µm. After calculating the required ablation depth, the residual stromal bed (RSB) after LASIK flap creation would be only 220 µm. What is the most appropriate surgical recommendation?
Correct. RSB <250–300 µm is a contraindication for LASIK. PRK (no flap, more surface ablation) or phakic IOL (no corneal ablation at all) are appropriate alternatives for high myopia in a thin cornea.
Safe LASIK requires an RSB of at least 250–300 µm to prevent post-operative corneal ectasia. At 220 µm, LASIK is contraindicated. Surface ablation (PRK, which has no flap) preserves more stroma, or a phakic IOL (implanted in the anterior or posterior chamber, leaving the cornea untouched) can correct high myopia without stromal ablation.
RSB of 220 µm is below the safe minimum of 250–300 µm for LASIK. A thinner flap does not solve the problem — the ablation depth is determined by the prescription, not the flap. PRK or phakic IOL are the correct alternatives.
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Which of the following is the correct sequence from least to worst visual impairment when vision falls below the 6/60 line on a Snellen chart?
Correct. The hierarchy below 6/60 is: CF → HM → PL → NPL. Count fingers implies the best residual vision; NPL is total blindness.
Below 6/60 the hierarchy of recorded VA is: Count Fingers (CF at x metres) → Hand Movements (HM) → Perception of Light (PL) → No Perception of Light (NPL, which represents total blindness). This sequence must be memorised correctly for clinical documentation and legal blindness classification.
The correct hierarchy below 6/60 is: Count Fingers → Hand Movements → Perception of Light → No Perception of Light. This sequence goes from better to worse visual function.
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A child with known left amblyopia is being treated with full-time patching of the right (dominant) eye. After 6 weeks, her mother reports that the child's right eye vision has become blurred. Refraction and VA of the right eye are now 6/18 (previously 6/6). What complication has most likely occurred?
Correct. Occlusion amblyopia is the most feared complication of patching therapy — the normal eye develops deprivation amblyopia from prolonged occlusion. Regular monitoring (every 4–8 weeks) is mandatory during patching.
Occlusion amblyopia is a well-recognised complication of patching: the previously normal dominant eye, when deprived of visual stimulation, can itself develop amblyopia — particularly in young children with high residual cortical plasticity. Prevention requires regular monitoring during patching (every 4–8 weeks) and avoiding full-time patching in very young children.
Reduced VA in the previously normal patched eye indicates occlusion amblyopia — a deprivation amblyopia induced by the patch itself. This is why monitoring during treatment is mandatory.
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A 50-year-old man was recently told he has hypermetropia (+3.00 D) for the first time in his life. He had no vision complaints until age 48. What physiological explanation best accounts for why hypermetropia can remain symptom-free until middle age?
Correct. Latent hypermetropia is masked by accommodation in younger patients. As presbyopia reduces accommodative amplitude, the latent error is unmasked — explaining new-onset symptoms in middle age.
Hypermetropia can be classified as latent (masked by accommodation) or manifest. In young adults, the crystalline lens can increase its curvature (accommodation) to bring the hypermetropic focal point forward onto the retina — masking the error. As accommodation amplitude declines with presbyopia, the lens can no longer compensate, and the previously latent hypermetropia becomes symptomatic.
The key concept is latent hypermetropia. Young, highly accommodative lenses can fully compensate for low-to-moderate hypermetropia. Presbyopic decline in accommodation unmasks the error.
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A child presents with complete right eyelid ptosis from birth (congenital ptosis). The right eye is otherwise structurally normal. Which type of amblyopia is this child most at risk of developing, and why?
Correct. Complete congenital ptosis obstructs light entry → form vision deprivation → deprivation amblyopia. This is the most severe type and requires urgent surgical correction in the first weeks to months of life.
Deprivation amblyopia results from any physical obstruction of the visual axis during the critical period — congenital ptosis, dense cataract, or corneal opacity. It is the most severe and most rapidly developing form of amblyopia. Complete ptosis covering the visual axis is an ophthalmic emergency in a neonate: surgical elevation of the lid is required urgently to prevent irreversible amblyopia.
Congenital ptosis obstructs the visual axis, causing deprivation amblyopia — the most rapidly developing and severe type. Urgent ptosis surgery is required, not observation. This is not strabismic or anisometropic amblyopia.
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A 25-year-old medical student consults you for refractive surgery. Slit-lamp examination and corneal topography reveal Munson's sign and inferior steepening with skewed radial axis on topography. Corneal pachymetry shows central thickness of 420 µm. What is the correct management?
Correct. Keratoconus is an absolute contraindication to ALL corneal laser surgery, including PRK. CXL halts progression; contact lenses manage the irregular astigmatism.
Munson's sign (V-shaped deformity of the lower lid on downgaze) and inferior topographic steepening with skewed radial axis are classical findings of keratoconus. All laser refractive surgery — including surface ablation (PRK) — is contraindicated in keratoconus because any reduction in stromal thickness accelerates ectasia. Management options include rigid gas-permeable contact lenses and corneal collagen cross-linking (CXL) to halt progression.
Keratoconus contraindicates all laser ablation — PRK included. Removing stroma from an already-weakened ectatic cornea accelerates progression. CXL + contact lenses are the correct approach.
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