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Refraction
Cataract & Refractive Surgery
Key Points
- •Total eye refractive power is +60 D: cornea +43 D (2/3, most powerful refracting surface at the air-cornea interface) and lens +15–20 D (1/3); emmetropic axial length 23.5 mm
- •Retinoscopy: with-movement = hypermetropia (add plus); against-movement = myopia (add minus); scissors reflex = keratoconus/irregular astigmatism; subtract +1.5 D for 67 cm working distance
- •Cycloplegic refraction is mandatory in children - cyclopentolate 1% (refract at 45 min) or atropine 1% (BD × 3 days); reveals latent hypermetropia; prescribe full cycloplegic correction for accommodative esotropia
- •Effectivity: for spectacle powers >±4 D, vertex distance matters - minus CL power is less minus than spectacles; plus CL power is more plus; formula: Fc = Fs / (1 − d × Fs)
- •Accommodation declines with age - Hofstetter's minimum: 15 − 0.25 × age; presbyopia becomes symptomatic around age 40–45; near add increases from +1.00 D (age 40) to +3.00 D (age 60+)
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12 more sections are included with the Clinical plan.
- Definition
- Epidemiology
- Aetiology and causes
- Pathogenesis
- Classification
- Clinical features