Lens and Cataract

LensLens

IntroductionIntroduction

• Emanation theory of visionEmanation theory of vision

• Celsus (25 BC-AD 50)Celsus (25 BC-AD 50)

• Andres VesaliusAndres Vesalius

• Fabricus ab AquapendenteFabricus ab Aquapendente

• Felix PlaterFelix Plater

AnatomyAnatomy

LensLens

http://en.wikipedia.org/wiki/Image:Schematic_diagram_of_the_human_eye_en.svg

THE LENSTHE LENS• Maintain its own clarityMaintain its own clarity

• To refract lightTo refract light

• To provide accomodationTo provide accomodation

• No blood supply or innervation after No blood supply or innervation after fetal developmentfetal development

• Zonular fibers of ZinnZonular fibers of Zinn

• Parts of the lens:Parts of the lens:– CapsuleCapsule– Lens epitheliumLens epithelium– CortexCortex– Nucleus Nucleus

LensLens

LensLens

• Index of refraction: 1.4 centrally; Index of refraction: 1.4 centrally; 1.36 peripherally1.36 peripherally

• Non accomodative state: 15-20 D of Non accomodative state: 15-20 D of convergent refractive power of the convergent refractive power of the average human eyeaverage human eye

• At birth: 6 mm equitorially; 3.5 mm At birth: 6 mm equitorially; 3.5 mm anteroposteriorlyanteroposteriorly– Wt: 90 mgWt: 90 mg

• Adult: 9 mm equitorially and 5 mm Adult: 9 mm equitorially and 5 mm anteroposteriorlyanteroposteriorly– Wt- 255 mgWt- 255 mg

LENS CAPSULE:LENS CAPSULE:

–Elastic, transparent Elastic, transparent basement membrane basement membrane

– Zonular lamellaZonular lamella

Lens CapsuleLens Capsule

Zonular FibersZonular Fibers

• Inserts 1.5 mm Inserts 1.5 mm onto the anterior onto the anterior lens capsule and lens capsule and posteriorly 1.5 mm posteriorly 1.5 mm onto the posterior onto the posterior lens capsulelens capsule

• 5-30 um in 5-30 um in diameterdiameter

Lens EpitheliumLens Epithelium

Nucleus & CortexNucleus & Cortex

Nucleus & CortexNucleus & Cortex

• Lens sutures- formed by the Lens sutures- formed by the arrangement of interdigitations of arrangement of interdigitations of apical cell processes (anterior apical cell processes (anterior sutures) and the basal processes sutures) and the basal processes (posterior sutures)(posterior sutures)

PhysiologyPhysiology

PhysiologyPhysiology

• Maintenance of lens water and cation Maintenance of lens water and cation balancebalance– The normal human lens contains The normal human lens contains

approximately 66% water and 33% approximately 66% water and 33% proteinprotein

– Na concentration is maintained at about Na concentration is maintained at about 20 mM 20 mM

– K concentration is about 120 mMK concentration is about 120 mM

Lens EpitheliumLens Epithelium

– Higher levels of K ions and amino acidsHigher levels of K ions and amino acids– Lower levels of Na ions, Cl ions and Lower levels of Na ions, Cl ions and

waterwater– NaK ATpase pump- inhibited by ouabainNaK ATpase pump- inhibited by ouabain

Pump-leak theoryPump-leak theory

Calcium HomeostasisCalcium Homeostasis

• Normal intracellular calcium level in Normal intracellular calcium level in the lens: 30 mMthe lens: 30 mM

• Exterior calcium levels: 2 uMExterior calcium levels: 2 uM• Ca ATpase pumpCa ATpase pump• Increase levels of Ca: Depressed Increase levels of Ca: Depressed

glucose metabolism, formation of high glucose metabolism, formation of high molecular wt protein aggregates and molecular wt protein aggregates and activation of destructive proteasesactivation of destructive proteases

• Active amino acid transport takes Active amino acid transport takes place at the lens epithelium place at the lens epithelium

• Glucose enters the lens by facilitated Glucose enters the lens by facilitated diffusiondiffusion

• The waste products of lens The waste products of lens metabolism leaves via simple metabolism leaves via simple diffusiondiffusion

BIOPHYSICSBIOPHYSICS•ACCOMODATIONACCOMODATION

– Classic theory of von HelmholtzClassic theory of von Helmholtz– STIMULUS :STIMULUS :

•Known or apparent size and distance Known or apparent size and distance of the object or by blurof the object or by blur

•Chromatic aberrationChromatic aberration

•Continual oscllation of cilliary tone Continual oscllation of cilliary tone

BIOPHYSICSBIOPHYSICS

AccomodationAccomodation

• Parasympathetic fibers of oculomotor Parasympathetic fibers of oculomotor nervenerve

• Amplitude of accomodation- amount of Amplitude of accomodation- amount of change in the eye’s refractive power change in the eye’s refractive power that is produced by accomodationthat is produced by accomodation– Parasympathomimetic drugs (Pilocarpine)Parasympathomimetic drugs (Pilocarpine)– Parasympatholytic drugs (Atropine)Parasympatholytic drugs (Atropine)

AccomodationAccomodation

• Adolescents- 12-16 DAdolescents- 12-16 D

• Adults at age 40- 4-8 DAdults at age 40- 4-8 D

• After age 50- 2 DAfter age 50- 2 D

PresbyopiaPresbyopia

• Loss of accomodation due to agingLoss of accomodation due to aging

• Von HemholtzVon Hemholtz

• Alternative theory by Schachar: Alternative theory by Schachar: – As the lens fibers accumulate within the As the lens fibers accumulate within the

capsular bag, the crystalline lens capsular bag, the crystalline lens increase in size such that there is little increase in size such that there is little or no room for lens movement with or no room for lens movement with cilliary muscle contraction cilliary muscle contraction

BiochemistryBiochemistry

Crystallin ProteinsCrystallin Proteins

BiochemistryBiochemistry

• Increase water insoluble proteins Increase water insoluble proteins with agewith age– Brunescent cataractsBrunescent cataracts

• Decrease in lens protein Decrease in lens protein concentration with ageconcentration with age– 81% in in adult transparent lenses81% in in adult transparent lenses– 51.4% in cataractous lenses51.4% in cataractous lenses– Escape of intact crystallins through the Escape of intact crystallins through the

lens capsulelens capsule

Glucose Metabolism in LensGlucose Metabolism in Lens

Oxidative Damage and Oxidative Damage and Protective MechanismProtective Mechanism

• Free radicals from radiant energyFree radicals from radiant energy

• Gluthataione, Vit E and Ascorbic acidGluthataione, Vit E and Ascorbic acid

THE NORMAL THE NORMAL AGING LENSAGING LENS

•MORPHOLOGICAL CHANGES:MORPHOLOGICAL CHANGES:– CAPSULE THICKENSCAPSULE THICKENS– EPITHELIAL NUCLEI BECOMES FLATTEREPITHELIAL NUCLEI BECOMES FLATTER– EPITHELIAL CELL DENSITY DECREASESEPITHELIAL CELL DENSITY DECREASES– (+)VACUOLES AND MULTILAMELLAR (+)VACUOLES AND MULTILAMELLAR

BODIESBODIES

THE NORMAL THE NORMAL AGING LENSAGING LENS•BIOPHYSICAL CHANGES:BIOPHYSICAL CHANGES:

– ULTRASTRUCTURAL ULTRASTRUCTURAL DETERIORATIONDETERIORATION

– TRANSPARENCY DECREASESTRANSPARENCY DECREASES– LOSS OF ACCOMODATIONLOSS OF ACCOMODATION

THE NORMAL THE NORMAL AGING LENSAGING LENS•PHYSIOLOGICAL CHANGES:PHYSIOLOGICAL CHANGES:

– DECREASE MEMBRANE DECREASE MEMBRANE POTENTIALPOTENTIAL

– POTASIUM - UNCHANGEDPOTASIUM - UNCHANGED– SODIUM - INCREASEDSODIUM - INCREASED– CALCIUM - INCREASEDCALCIUM - INCREASED

THE NORMAL THE NORMAL AGING LENSAGING LENS•BIOCHEMICAL CHANGES:BIOCHEMICAL CHANGES:

– METABOLIC ACTIVITIES SLOW METABOLIC ACTIVITIES SLOW DOWNDOWN

– ENZYME ACTIVITIES ARE REDUCEDENZYME ACTIVITIES ARE REDUCED– ALL STRUCTURAL PROTEINS ALL STRUCTURAL PROTEINS

UNDERGO POSTTRANSLATIONAL UNDERGO POSTTRANSLATIONAL MODIFICATIONSMODIFICATIONS

EmbryologyEmbryology

EmbryologyEmbryology

• 25 days AOG- 2 25 days AOG- 2 lateral outpouching lateral outpouching called the optic called the optic vesicles are formedvesicles are formed

• Become closely Become closely related to surface related to surface ectoderm as they ectoderm as they enlargedenlarged

Lens PlateLens Plate

• 27 days AOG- cells of 27 days AOG- cells of the surface ectoderm the surface ectoderm become columnarbecome columnar

• This area of thickened This area of thickened cells is called the lens cells is called the lens plate or lens placodeplate or lens placode

• 29 days AOG- lens pit 29 days AOG- lens pit appears as a small appears as a small indentation inferior to indentation inferior to the center of the lens the center of the lens plateplate

Lens VesiclesLens Vesicles

• As the lens pit As the lens pit invaginates the invaginates the stalk that connects stalk that connects it to the ectoderm it to the ectoderm dissapeardissapear

• The resultant The resultant sphere is called the sphere is called the lens vesiclelens vesicle

• As the lens vesicle As the lens vesicle is forming, the is forming, the optic vesicle is optic vesicle is undergoing a undergoing a process of process of invagination as it invagination as it begings to form begings to form the 2 layered optic the 2 layered optic cup cup

• 35 wks AOG- 35 wks AOG- formation of formation of primary lens fibersprimary lens fibers

• 40 wks AOG- the 40 wks AOG- the lumen of the lens lumen of the lens vesicles is completely vesicles is completely obliterated.obliterated.

• The elongated cells The elongated cells are called the primary are called the primary lens fiberslens fibers

• The cells of the The cells of the anterior lens vesicles anterior lens vesicles do not change- lens do not change- lens epitheliumepithelium

• Lens capsule Lens capsule develops as a develops as a basement basement membrane membrane elaborated by the elaborated by the lens epithelium lens epithelium anteriorly and by anteriorly and by the lens fibers the lens fibers posteriorlyposteriorly

• 7 wks AOG- the 7 wks AOG- the lens epithelium in lens epithelium in the area of the the area of the equator begin to equator begin to multiply rapidly multiply rapidly and elongate to and elongate to form the secondary form the secondary lens fiberslens fibers

• The secondary lens The secondary lens fibers formed fibers formed between 2 and 8 between 2 and 8 months of months of gestation make up gestation make up the fetal nucleusthe fetal nucleus

Lens Sutures and Fetal Lens Sutures and Fetal NucleusNucleus• Y shaped sutures- Y shaped sutures-

8 wks AOG8 wks AOG

• Erect Y sutures- Erect Y sutures- anterioranterior

• Inverted Y sutures- Inverted Y sutures- posteriorposterior

• Only during fetal Only during fetal life are Y sutures life are Y sutures formedformed

Tunica Vasculosa LentisTunica Vasculosa Lentis

• 1 mo AOG- the hyaloid 1 mo AOG- the hyaloid artery gives rise to artery gives rise to small capillariessmall capillaries

• Posterior vascular Posterior vascular capsulecapsule

• Capsulopapillary portion Capsulopapillary portion of the tunica vasculosa of the tunica vasculosa lentislentis

• Anterior vascular Anterior vascular capsule- fully developed capsule- fully developed around 9 wks AOG around 9 wks AOG – Mittendorf dotMittendorf dot

Congenital Anomalies and Congenital Anomalies and AbnormalitiesAbnormalities

LENS LENS ALTERATIONSALTERATIONS

•ANOMALIES IN LENS ANOMALIES IN LENS SIZESIZE– MICROPHAKIAMICROPHAKIA

ANOMALIES IN LENS ANOMALIES IN LENS SHAPESHAPE

– ANTERIOR ANTERIOR LENTICONUS/LENTIGLOBUS:LENTICONUS/LENTIGLOBUS:•ANTERIOR SURFACE PROTRUDESANTERIOR SURFACE PROTRUDES

CONICAL - LENTICONUSCONICAL - LENTICONUSSPHERICAL - LENTIGLOBUSSPHERICAL - LENTIGLOBUS

POSTERIOR POSTERIOR LENTICONUSLENTICONUS//LENTIGLOBUSLENTIGLOBUS

•MORE COMMON MORE COMMON THAN ANTERIORTHAN ANTERIOR

•PROMINENT PROMINENT SPHEROID SPHEROID ELEVATION ON ELEVATION ON THE POSTERIOR THE POSTERIOR SURFACE OF SURFACE OF THE LENSTHE LENS

ANOMALIES IN LENS ANOMALIES IN LENS SHAPESHAPE

– COLOBOMA OF COLOBOMA OF THE LENSTHE LENS•CHARACTERIZED BY CHARACTERIZED BY

NOTCHING OF THE NOTCHING OF THE INFERIOR EQUATOR INFERIOR EQUATOR OF THE LENSOF THE LENS

•CATARACTOUSCATARACTOUS•UNILATERALUNILATERAL•ASSOCIATED WITH ASSOCIATED WITH

COLOBOMAS OF COLOBOMAS OF THE IRIS AND THE IRIS AND CHOROIDCHOROID

Mittendorf DotMittendorf Dot

• Remnant of the posterior vascular Remnant of the posterior vascular capsule of the tunica vasculosa lentis capsule of the tunica vasculosa lentis

• Small, dense, white spot generally Small, dense, white spot generally located inferonasal to the posterior located inferonasal to the posterior pole of the lenspole of the lens

Epicapsular starEpicapsular star

• Remnant of the Remnant of the tunica vasculosa tunica vasculosa lentislentis

• Chicken tracksChicken tracks

Peters AnomalyPeters Anomaly

• Anterior segment dysgenesis Anterior segment dysgenesis syndromesyndrome

• Central or paracentral corneal Central or paracentral corneal opacity associated with thinning of opacity associated with thinning of adjacent or absence of endothelium adjacent or absence of endothelium and Descemets membraneand Descemets membrane

Congenital & Infantile Congenital & Infantile CataractCataract

DEVELOPMENTAL DEVELOPMENTAL CATARACTCATARACT

• SUTURE CATARACTSUTURE CATARACT– OPACITIES ALONG THE LINES OF THE Y OPACITIES ALONG THE LINES OF THE Y

SUTURESSUTURES– ALMOST ALWAYS BILATERALALMOST ALWAYS BILATERAL– RARELY CAUSES VISUAL SYMPTOMSRARELY CAUSES VISUAL SYMPTOMS

Polar cataractsPolar cataracts

• Lens opacities that involve the Lens opacities that involve the subcapsular cortex and the lens capsule subcapsular cortex and the lens capsule of the anterior and posterior pole of the of the anterior and posterior pole of the lenslens

• Anterior polar cataracts- small, bilateral, Anterior polar cataracts- small, bilateral, symmetric opacities that don’t impair symmetric opacities that don’t impair vsionvsion

• Posterior polar cataracts- larger and Posterior polar cataracts- larger and impair visionimpair vision


• CERULEAN CATARACTCERULEAN CATARACT– BLUE-DOT CATARACTBLUE-DOT CATARACT– SMALL PUNCTIFORM OPACITIES IN THE SMALL PUNCTIFORM OPACITIES IN THE

ADULT NUCLEUS AND CORTEXADULT NUCLEUS AND CORTEX

Nuclear CataractsNuclear Cataracts

• Opacities of either Opacities of either the embryonic the embryonic nucleus alone or nucleus alone or both the embryonic both the embryonic and fetal nucleiand fetal nuclei

• Usually bilateralUsually bilateral

Capsular CataractsCapsular Cataracts

• Small opacifications of the lens Small opacifications of the lens epithelium and the anterior lens epithelium and the anterior lens capsule that spare the cortex capsule that spare the cortex

Lamellar CataractsLamellar Cataracts

• Most common type of congenital/ Most common type of congenital/ infantile cataractinfantile cataract

• Bilateral and symmetricBilateral and symmetric

• Opacifications of specific layers or Opacifications of specific layers or zones of lens zones of lens

Complete CataractsComplete Cataracts

• All of the lens fibers are opacifiedAll of the lens fibers are opacified

Membranous CataractsMembranous Cataracts

• Lens proteins are Lens proteins are resorbed from resorbed from either an intact or either an intact or traumatized lens traumatized lens and posterior lens and posterior lens capsule to fuse into capsule to fuse into white membranewhite membrane


• RUBELLA RUBELLA CATARACTCATARACT

– MATERNAL MATERNAL INFECTION WITH INFECTION WITH RUBELLA VIRUS RUBELLA VIRUS DURING FIRST TRIM DURING FIRST TRIM OF PREGNANCYOF PREGNANCY

– Pearly white nuclear Pearly white nuclear opacificationopacification

AAGGEEDDEEPPEENNDDEENNTTCCAATTAARRAACCTT

AGE DEPENDENT AGE DEPENDENT CATARACTCATARACT

•SUBCAPSULAR CATARACTSUBCAPSULAR CATARACT– ANTERIOR SUBCAPSULARANTERIOR SUBCAPSULAR– POSTERIOR SUBCAPSULARPOSTERIOR SUBCAPSULAR

•NUCLEAR CATARACTNUCLEAR CATARACT

•CORTICAL CATARACTCORTICAL CATARACT

NUCLEAR CATARACTNUCLEAR CATARACT

– EXAGGERATION OF EXAGGERATION OF THE PHYSIOLOGIC THE PHYSIOLOGIC SCLEROTIC CHANGESCLEROTIC CHANGE

– OFTEN ASSOCIATED OFTEN ASSOCIATED WITH MYOPIA - INC WITH MYOPIA - INC REFRACTIVE INDEXREFRACTIVE INDEX

– ““SECOND SIGHT OF SECOND SIGHT OF THE AGED”THE AGED”

Nuclear CataractNuclear Cataract


• CORTICAL CATARACTCORTICAL CATARACT– MOST COMMON FORM OF LENS OPACITYMOST COMMON FORM OF LENS OPACITY– STARTS AS VACUOLES AND CLEFTS STARTS AS VACUOLES AND CLEFTS

BETWEEN LENS BETWEEN LENS FIBERSFIBERS

Cortical CataractCortical Cataract

Mature Cortical CataractMature Cortical Cataract

Hypermature Cortical Hypermature Cortical CataractCataract

Morgagnian CataractMorgagnian Cataract


•ANTERIOR SUBCAPSULAR ANTERIOR SUBCAPSULAR CATARACTCATARACT– LIES DIRECTLY UNDER THE LENS CAPSULELIES DIRECTLY UNDER THE LENS CAPSULE– ASSOCIATED WITH FIBROUS METAPLASIA OF ASSOCIATED WITH FIBROUS METAPLASIA OF

THE THE ANTERIOR EPITHELIUMANTERIOR EPITHELIUM

Poesterior Subcapsular Poesterior Subcapsular CataractCataract


•POSTERIOR SUBCAPSULAR CATARACTPOSTERIOR SUBCAPSULAR CATARACT– LIES JUST IN FRONT OF THE POSTERIOR CAPSULELIES JUST IN FRONT OF THE POSTERIOR CAPSULE– POSTERIOR MIGRATION OF THE EPITHELIAL CELLS POSTERIOR MIGRATION OF THE EPITHELIAL CELLS

OF THE LENSOF THE LENS

MORGAGNIAN MORGAGNIAN CATARACTCATARACT

TTRRAAUUMMAATTIICCCCAATTAARRAACCTT

TRAUMATIC TRAUMATIC CATARACTCATARACT

• MOST COMMON CAUSE OF MOST COMMON CAUSE OF UNILATERAL CATARACT IN YOUNG UNILATERAL CATARACT IN YOUNG INDIVIDUALINDIVIDUAL

• DIRECT PENETRATING INJURYDIRECT PENETRATING INJURY

• CONCUSSIONCONCUSSION

• ELECTRIC SHOCK - RAREELECTRIC SHOCK - RARE

TRAUMATIC TRAUMATIC CATARACTCATARACT

•TRAUMATIC TRAUMATIC ROSETTE-ROSETTE-SHAPED SHAPED CATARACTCATARACT– STELLATE CATARACTSTELLATE CATARACT– TYPICAL PICTURE TYPICAL PICTURE

AFTER BOTH AFTER BOTH CONCUSSION AND CONCUSSION AND

PERFORATING INJURIESPERFORATING INJURIES

Dislocation & SubluxationDislocation & Subluxation

• Fluctuation of visionFluctuation of vision

• Impaired accomodationImpaired accomodation

• High astigmatismHigh astigmatism

Radiation Induced CataractsRadiation Induced Cataracts

•Ionizing radiation in x-ray Ionizing radiation in x-ray range (0.001-10 nm can range (0.001-10 nm can cause cataracts in some cause cataracts in some individuals in dosages as individuals in dosages as low as 200 rads per low as 200 rads per fractionfraction

• Infrared radiationInfrared radiation

• Ultraviolet radiation- 290-320 nmUltraviolet radiation- 290-320 nm

• Microwave radiationMicrowave radiation

• Chemical injuriesChemical injuries

Intralenticular Foreign BodyIntralenticular Foreign Body

• Siderosis BulbiSiderosis Bulbi– Deposition of iron molecules in the Deposition of iron molecules in the

trabecular meshwork, lens epithelium, trabecular meshwork, lens epithelium, iris and retinairis and retina

– Complete cortical cataract and retinal Complete cortical cataract and retinal dysfunctiondysfunction

• Chalcosis- sunflower cataractChalcosis- sunflower cataract

Drug Induced CataractsDrug Induced Cataracts

– Corticosteroids Corticosteroids – PhenothiazinesPhenothiazines– MioticsMiotics– AmiodaroneAmiodarone

–Statins Statins

Metabolic CataractsMetabolic Cataracts

• Diabetes MellitusDiabetes Mellitus– Can affect the clarity of the lens, its Can affect the clarity of the lens, its

refractive index and accomodative refractive index and accomodative amplitudeamplitude

– 2 types:2 types:•True diabetic cataract or snowflake cataractTrue diabetic cataract or snowflake cataract

•Senescent cataractSenescent cataract

GalactosemiaGalactosemia

• Inherited AR inability to convert Inherited AR inability to convert galactose to glucosegalactose to glucose

• Classic galactosemia- most common Classic galactosemia- most common and most severe formand most severe form– Malnutrion, hepatomegaly, jaundice and Malnutrion, hepatomegaly, jaundice and

mental deficiencymental deficiency– 75% will develop cataract75% will develop cataract– Oil droplet appearanceOil droplet appearance

Thank You!Thank You!

Documents

Lens and Cataract