lens i 13.04.16,dr.n.swathi

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