lens i 06.04.17,dr.n.swathi
TRANSCRIPT
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LENS - IDr.Swathi.NMGMC & RI
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• Anatomy
• Position abnormalities of lens
• Etiopathogenesis
• Classification
• Special types of cataract
Objectives :
Of cataract
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Transparent
Biconvex
Elliptical
Avascular
Crystalline appearance
Located between the iris and the vitreous
In patellar fossa
Suspended by zonules
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equatorial diameter (adult) : 9-10mm axial width : 3.5 - 4.0mm at birth,
about 4mm at 40 years 4.75 to 5.0 mm in extreme old
age.
Physiological change observed daily?
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varies markedly with accommodation
radius of curvature – anterior surface : 10 mm (changes to 6 mm on accomodation)
posterior surface : 6mm
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Refractive index : 1.39
Dioptric contribution :15 D
Accommodative power : 15-16 D : At birth 7-8 D : 25 years
2 D : 50 years.
Why decrease with age?
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Abnormalities in the lens:
Shape / sizePositionTransparency
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Abnormal shape / size :
• Coloboma• Spherophakia• Microphakia• Microspherophakia – ass. with Weil-Marchesani syndrome
Persistent hyperplastic primary vitreousPosterior / anterior lenticonus
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Microspherophakia
Coloboma
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Persistent hyperplastic primary vitreous
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Anterior / Posterior lenticonus
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Abnormal position
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Cataract
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Etiopathogenesis :
• Degeneration & opacification of formed lens fibres
• Formation of aberrant lens fibres• Deposition of other materials
• Abnormality of lens proteins – disturbance of intra- & extra- cellular equilibrium of water & electrolytes
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• Hydration
• Denaturation
• Slow sclerosis
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Morphological classification of cataract
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Congenital / Developmental cataract :
• Blue dot cataract
• Sutural cataract – anterior / posterior
• Cataracta centralis pulverulenta
• Zonular cataract
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• Fusiform / coralliform
• Nuclear cataract
• Coronary cataract
• Anterior/ postrior polar cataract
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Associated with ocular diseases :
Complicated cataract
• posterior cortical / posterior subcapsular
• polychromatic lustre• Breadcrumb appearance
• Iridocyclitis , ciliary body tumour, choroiditis, degenerative myopia, retinitis pigmentosa, retinal detachment
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Associated with systemic diseases :• Diabetic – snowflake cataract• Parathyroid tetany – anterior / posterior
punctate subcapsular opacity
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• Myotonic dystrophy – christmas tree cataract• Galactosemia – oil droplet cataract• Down syndrome – punctate subcapsular
opacities• Atopic cataract
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Due to other causes :• Heat / infrared cataract • Irradiation cataract• Electric cataract• Traumatic cataract – rosette cataract
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• Enumerate the cause of cataract in a given age group (child, middle aged, elderly)
• Zonular cataract• Traumatic cataract• Complicated cataract• Subluxated lens• Diagnosis of cataract• Congenital cataract• Diabetic cataract
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Suggested reading
• Etiopathogenesis of cataract
• Symptoms of cataract
• Complications of cataract
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