lens i 06.04.17,dr.n.swathi
TRANSCRIPT
LENS - IDr.Swathi.NMGMC & RI
• Anatomy
• Position abnormalities of lens
• Etiopathogenesis
• Classification
• Special types of cataract
Objectives :
Of cataract
Transparent
Biconvex
Elliptical
Avascular
Crystalline appearance
Located between the iris and the vitreous
In patellar fossa
Suspended by zonules
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?
varies markedly with accommodation
radius of curvature – anterior surface : 10 mm (changes to 6 mm on accomodation)
posterior surface : 6mm
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?
Abnormalities in the lens:
Shape / sizePositionTransparency
Abnormal shape / size :
• Coloboma• Spherophakia• Microphakia• Microspherophakia – ass. with Weil-Marchesani syndrome
Persistent hyperplastic primary vitreousPosterior / anterior lenticonus
Microspherophakia
Coloboma
Persistent hyperplastic primary vitreous
Anterior / Posterior lenticonus
Abnormal position
Cataract
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
• Hydration
• Denaturation
• Slow sclerosis
Morphological classification of cataract
Congenital / Developmental cataract :
• Blue dot cataract
• Sutural cataract – anterior / posterior
• Cataracta centralis pulverulenta
• Zonular cataract
• Fusiform / coralliform
• Nuclear cataract
• Coronary cataract
• Anterior/ postrior polar cataract
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
Associated with systemic diseases :• Diabetic – snowflake cataract• Parathyroid tetany – anterior / posterior
punctate subcapsular opacity
• Myotonic dystrophy – christmas tree cataract• Galactosemia – oil droplet cataract• Down syndrome – punctate subcapsular
opacities• Atopic cataract
Due to other causes :• Heat / infrared cataract • Irradiation cataract• Electric cataract• Traumatic cataract – rosette cataract
• 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
Suggested reading
• Etiopathogenesis of cataract
• Symptoms of cataract
• Complications of cataract