LENS

LENSIt is a highly organized

transparent spheroid structure that has evolved to perform

refraction of the light entering in the eye. It does not posses

nerve, blood vessels or connective tissue.

Anatomy of LENSBiconvex LensDiameter varies from 8.8 to 9.2 (9mm)Lens grow in size continuously throughout life.

Its weight is about 60 mgm at the birth and up-to 250 mgm by 80 years of age.

Antero-posterior thickness changes with accommodation. Thickness is 4.75 – 5 mm (4.5mm) (un-accommodated) in adults.

Circumference is known as equator

Anatomy of LENS

Lens is suspended in eye by Zonules which are inserted on anterior surface and equatorial lens capsule and attached to ciliary body(Pars Plicata- Ciliary Processes) .

Zonular fibres are series of fibrillin rich fibre.

Anatomy of LENS

Histologically lens consists of three major components:

1. Capsule – is a thick collagenese basement membrane which is transparent, elastic acellular envelop, thick at anterior pre-equatorial region (21 micron m), thinnest at the posterior pole (4 micron m). Anterior pole is approximately 14 micron m thick.

Anatomy of LENS 2. Lens Epithelium – It is a single layer of

cells lining the anterior capsule and extends to the equatorial lens bow.

Zone of epithelial cells:a. Central – cells do not actively divide,

they divide under pathological conditions only. b. Pre-equatorial germinal zone : cells

rarely divide.

Anatomy of LENS

C. Germinal zone: constitute of the stem cell population. The newly formed cells from germinal zone are forced into transitional zone where they elongate and differentiate to form mass of the lens. The lens capsule regulate the transport of metabolite, nutrients and electrolytes to the lens fibers.

Anatomy of LENS

3. Lens substance: It constitute the main mass of the lens. It is divided into-

a. Nucleusb. CortexNucleus: consists of(i) Embryonic nucleus (it contains

primary lens fibres that are formed in lens vesicle)

Anatomy of LENS

(ii) Fetal nucleus: it contains embryonic nucleus and all fibres added to the lens before birth (iii) Infantile nucleus: it contains embryonic , fetal nucleus together with all the fibres added up-to the age of 4 years. (iv) Adult nucleus: composed of all fibres added before sexual maturation The nucleus consists of densely compacted lens fibres and higher refractive index than cortex.

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LENS Anatomy

Capsule

Cortex

3

45

6

3 – Adult Nu 4 - Infantile Nu5 – Foetal Nu6 – Embryonic Nu.

Lens Cortex It is located peripherally and is composed

of secondary fibres formed continuously after sexual maturation. It is further

divided into: Deep cortexIntermediate cortexSuperficial cortex

LENS- Crystalline

Lens fibres contain high concentrations of crystalline.

Crystalline represent the major protein of the lens (constitute 90% of total protein content of lens). Crystalline has the following constituents:Alpha Beta and,Gamma

Lens - FunctionsThe lens serves two major

functions:Focusing of visible light rays on the

fovea Preventing damage from ultra-violet

radiation by reaching the retina

Lens – Physiology Lens function and transparency is

dependant on the supply of appropriate nutrient to its various structures. Metabolic needs of a adult lens is met by the aqueous and vitreous.

There is continuous transport of ions into and out of the lens.

Lens – Physiology The transparency is dependent on highly

organized structure of lens, dense packing of crystalline. Avascularity, absence of pigments and optimal hydration.

By act of accommodation it changes focusing power. Accommodation occurs by increasing the curvature of anterior surface thereby changing refractive power of lens.

Light transmission and elasticity of lens decreases with age.

CATARACTAny opacity in the lens or its capsule, whether

developmental or acquired is called cataract.

Developmental opacities are usually partial and stationary, whereas acquired opacities are progressive. They progress until the entire lens is involved, but exceptions are well known in both types.

Classification of Cataract

Classification based on EtiologyClassification based on

MorphologyClassification based on MaturityClassification based on the Age

of onset

Classification based on Etiology

DevelopmentalAcquired

Developmental

HereditaryIntrauterine causeso Rubellao Toxoplasmosiso CMVo Steroids

Acquired Cataract1. Age related (senile)2. Secondary cataract (Chronic Uveitis, ACG)3. Cataract associated with ocular diseases4. Cataract associated with systemic diseases

(pre-senile) (Diabetes, galactosemia etc)5. Traumatic Cataract6. Drug induced cataract (Steroids and others)

Classification based on Morphology

Capsular (Ant and Post)Subcapsular (Ant and Post)NuclearCortical

Classification based on Maturity

ImmatureMatureHypermatureMorgagnian

Classification based on the Age of onset

CongenitalInfantileJuvenilePresenileSenile

Risk Factors for Cataract

SenilitySunlight (specially UV –A and UV-B component)Severe Diarrheal dehydrationVitamin A,C, E deficiencyDiabetesSmokingCorticosteroidsGenetic

Pathogenesis of Cataract Caused by degeneration and opacification of

existing lens fibres, formation of aberrant fibres or deposition of other material in their place.

Factors causing disturbance of critical intra – and extra-cellular equilibrium of water and electrolyte or deranges the colloid system within the fibres tends to bring about opacification.

Pathogenesis of Cataract

Fibrous metaplasia of fibres (in complicated cataract)

Epithelial cell necrosis (Glaucomflecken)Deposition of abnormal products of

metabolism, drugs or metals.

Pathogenesis of Cataract

Biochemical Processeso Hydrationo Denaturation of Lens Proteinso Sclerosis

Pathogenesis of Cataract

The Changes in the Epithelial Cells and the Capsule

Changes in the Lenticular FibresSclerosis

Symptoms of Cataract1. Blurring of vision2. Frequent change of glasses due to rapid

change in refractive index of the lens 3. Painless, progressive gradual diminution of

vision due to reduction in transparency of the lens

4. Second sight or myopic shift in case of nuclear cataract causing index myopia, improving near vision.

Symptoms of Cataract

5. Loss or marked diminution of vision in bright sunlight or bright light beam in central posterior subcapsular cataract.

6. Monocular diplopia or polyopia in presence of cortical spoke opacities

7. Glare in posterior subcapsular cortical cataract due to increased scattering of light

Symptoms of Cataract

8. Colored haloes around the light as seen in cortical cataract due to irregular refractive index in different parts of the lens.

9. Color shift , reds are accentuated10. Visual field loss, generalized reduction

in sensitivity due to loss of transparency

Disturbances in VisionAppearance of Black SpotsReduction of Visual Fields Uni ocular PolyopiaLenticular MyopiaChanges in Colour values

Differential Diagnosis of painless gradual diminution of vision

Chronic open angle glaucomaMacular degenerationOptic atrophyCorneal dystrophyRetinopathy associated with systemic

disorders (hypertension or diabetes)

AssessmentVisual AcuityDirect Distant Ophthalmoscopy

(Fundal Glow)Light ReflexSlit Lamp Examination

ManagementMedicalSurgical

Medical ManagementRefractionDark Glasses

Surgical Management

IndicationsVisual ImprovementMedical IndicationsCosmetic Indications

Surgical ManagementCouchingIntracapsular Cataract Extraction

(ICCE)Extracapsular Cataract Extraction

(ECCE)Phacoemulsification

Clinical Rotation of 3rd YearSurgical TechniquesComplicationsManagement of complications

Ectopia LentisAquired (Trauma, Large eye ball, High

Myopia)

Hereditary o Marfans Syndromeo Homocystinuriao Weil Marchesani Syndrome

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