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EMBRYOLOGY , ANATOMY ,
PHYSIOLOGY, APPLIED
ANATOMY OF LENS
BY Dr. Rahul
MODERATOR Dr. Monica
Embryology of lens
 Formation of crystalline lens begins very early in
embryogenesis
 At about 25 days of gestation, 2 l...
lens pit or fovea lentis
 Appears at 29 days of gestation
 As small indentation inferior to center of lens plate
 The l...
 the lens vesicle was formed through a process of
invagination of surface ectoderm , so the apices of cells
oriented towa...
 Lens capsule develop as basement membrane from lens
epithelium anteriorly ,and lens fiber posteriorly
Secondary lens fib...
 The nuclei of primary lens fiber moves from posterior to
anterior position within lens fibre
 And subsequently become p...
Lens sutures and fetal nucleus
 Lens fiber grows anteriorly and posteriorly ,these
fibers meet with each other,this patte...
Y-shaped sutures of the fetal
nuclear fibres
Tunica vasculosa lentis
 As lens develops , nutritive support structure , the tunica
vasculosa lentis forms around it.
 ...
Congenital anomalies
 Congenital aphakia
 Lenticonus and lentiglobus
 Lens coloboma
 Mittendorf dot
 Epicapsular star...
POSTERIOR Lenticonus
Lens coloboma
Epicapsular star
Lens Development
lens placode in surface ectoderm
invaginates as lens vesicle
supplied by hyaloid artery
Lens
 The lens is a transparent, biconvex, crystalline
structure placed between iris and the vitreous in
a saucer shaped ...
 It has got two surfaces:
 the anterior surface is less convex (radius of curvature 10
mm) than the posterior (radius of...
 Lens is suspended in eye by Zonules which are
inserted on anterior surface and equatorial lens
capsule and attached to c...
Lens - Anatomy
 Histologically lens consists of three major
components:
1. Capsule –
 It is a thin, transparent, hyaline...
 2. Anterior epithelium.
 It is a single layer of cuboidal cells which lies deep
to the anterior capsule.
 In the equat...
 3. Lens fibres.
 The epithelial cells elongate to form lens fibres
which have a complicated structural form.
 Mature l...
 i. Nucleus.
 It is the central part containing the oldest fibres.
 It consists of different zones
 Which are laid dow...
Embryonic nucleus.
 It is the innermost part of nucleus which corresponds to
the lens upto the first 3 months of gestatio...
Fetal nucleus.
It lies around the embryonic nucleus, corresponds to
lens from 3 months of gestation till birth.
Its fibres...
Lens Cortex
Cortex. It is the peripheral part which comprises
the youngest lens fibres
 It is located peripherally and i...
Lens Cortex
 The region between embryonic and fetal nuclear core
and soft cortex i.e. infantile and adult nucleus is
some...
 4. Suspensory ligaments of lens (Zonules of Zinn).
 Also called as ciliary zonules,
 these consist essentially of a se...
 These fibres are arranged in three groups:
i. The fibres arising from pars plana and anterior
part of ora serrata pass a...
Lens - Crystalline
Lens fibres contain high concentrations of crystallins.
Crystallins represent the major proteins of the...
Lens - Functions
 The lens serves two major functions:
 Focusing of visible light rays on the fovea
 Preventing damagin...
Lens - Physiology
 Lens function is dependent on the metabolism of
glucose to produce energy , protein synthesis and a
co...
 The crystalline lens is a transparent structure playing main
role in the focussing mechanism for vision.
 Its physiolog...
 Avascularity,
 Tightly-packed nature of lens cells,
 The arrangement of lens proteins,
 Semipermeable character of le...
Pump leak theory
ACCOMMODATION
 As we know that in an emmetropic eye, parallel rays of
light coming from infinity are brought to focus on ...
APPLIED ANATOMY
 ANOMALIES OF
ACCOMMODATION
 Anomalies of accommodation are not uncommon.
 These include:
 (1) Presbyo...
Thank You
Embryology applied anatomy and physiology of lens
Embryology applied anatomy and physiology of lens
Embryology applied anatomy and physiology of lens
Embryology applied anatomy and physiology of lens
Embryology applied anatomy and physiology of lens
Embryology applied anatomy and physiology of lens
Embryology applied anatomy and physiology of lens
Embryology applied anatomy and physiology of lens
Embryology applied anatomy and physiology of lens
Embryology applied anatomy and physiology of lens
Embryology applied anatomy and physiology of lens
Embryology applied anatomy and physiology of lens
Embryology applied anatomy and physiology of lens
Embryology applied anatomy and physiology of lens
Embryology applied anatomy and physiology of lens
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Embryology applied anatomy and physiology of lens

Embryology applied anatomy and physiology of lens

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Embryology applied anatomy and physiology of lens

  1. 1. EMBRYOLOGY , ANATOMY , PHYSIOLOGY, APPLIED ANATOMY OF LENS BY Dr. Rahul MODERATOR Dr. Monica
  2. 2. Embryology of lens  Formation of crystalline lens begins very early in embryogenesis  At about 25 days of gestation, 2 lateral out pouching called optic vesicles form from forebrain  As optic vesicles enlarge,they become closely apposed to surface ectoderm  Lens plate  Cells of surface ectoderm that overlie optic vesicles become columnar at about 27 days of gestation  This area of thickened cells is called lens plate or lens placode.
  3. 3. lens pit or fovea lentis  Appears at 29 days of gestation  As small indentation inferior to center of lens plate  The lens pit deepens by process of cellular multiplication and invagination Lens vesicle  As the lens pit continue to invaginate ,the stalk of cells that connects it to surface ectoderm consticts and eventually disappears  The resultant sphere is called lens vesicle
  4. 4.  the lens vesicle was formed through a process of invagination of surface ectoderm , so the apices of cells oriented toward lumen of lens vesicle , with base at periphery  At same time optic vesicle is undergoing a process of invagination as it begins to form 2 layered optic cup Primary lens fibers and embryonic nucleus  The posterior cells of lens vesicle become more columnar and to elongate  They obliterate lumen of lens vesicle completely around 40 days.  These cells are primary lens fibres
  5. 5.  Lens capsule develop as basement membrane from lens epithelium anteriorly ,and lens fiber posteriorly Secondary lens fiber  At about 7 week of gestation ,lens epithelium in area of equator begin to multiply and elongate rapidly to form secondary lens fibers  The new lens fibers are continully fomed,layer upon layer  The secondary lens fiber between 2 and 8 months of gestaion make up fetal nucleus
  6. 6.  The nuclei of primary lens fiber moves from posterior to anterior position within lens fibre  And subsequently become pyknotic  These primary lens fiber make up embryonic nucleus that will occupy central area of lens in adult life  Posterior layer of optic vesicle undergo marked differention to form primary lens fiber  But cells of anterior lens vesicle do not change .this monolayer refer to as lens epithelium
  7. 7. Lens sutures and fetal nucleus  Lens fiber grows anteriorly and posteriorly ,these fibers meet with each other,this pattern known as sutures.  Y shaped are recognizable at about 8 weeks of gestation .  An erect Y suture appearing anteriorly and inverted y suture posteriorly  Only during fetal life Y sutures formed.  Later on pattern of lens suture s becomes increasingly complex  At birth lens weighs 90 mg and increases in mass at rate of 2mg per yr
  8. 8. Y-shaped sutures of the fetal nuclear fibres
  9. 9. Tunica vasculosa lentis  As lens develops , nutritive support structure , the tunica vasculosa lentis forms around it.  At about 1 month of gestation ,hyloid artery gives rise to small capillaries that form anastomtic net covering posterior aspect .  These small capillaries grows towards equator of lens where they anastomose with choroidal veins and form capsulopupillary portion of tunica vasculosa lentis  Branches of long ciliary arteries anastomos with branches of capsulopupillary portion to form anterior vascular capsule  It is fully developed at 9 weeks of gestation disapper shortly after birth
  10. 10. Congenital anomalies  Congenital aphakia  Lenticonus and lentiglobus  Lens coloboma  Mittendorf dot  Epicapsular star  Peters anomaly
  11. 11. POSTERIOR Lenticonus
  12. 12. Lens coloboma
  13. 13. Epicapsular star
  14. 14. Lens Development lens placode in surface ectoderm invaginates as lens vesicle supplied by hyaloid artery
  15. 15. Lens  The lens is a transparent, biconvex, crystalline structure placed between iris and the vitreous in a saucer shaped depression the patellar fossa.  Biconvex shape results from the anterior surface being less convex then posterior surface.  Its diameter is 9-10 mm and thickness varies with age from 3.5 mm (at birth) to 5 mm (at extreme of age). Its weight varies from 135 mg (0-9 years) to 255 mg (40-80 years of age).
  16. 16.  It has got two surfaces:  the anterior surface is less convex (radius of curvature 10 mm) than the posterior (radius of curvature 6 mm).  These two surfaces meet at the equator.  Its refractive index is 1.39 and total power is 15-16 D.  The accommodative power of lens varies with age, being 14-16 D (at birth); 7-8 D (at 25 years of age) and 1-2 D (at 50 years of age).
  17. 17.  Lens is suspended in eye by Zonules which are inserted on anterior surface and equatorial lens capsule and attached to ciliary body. Zonular fibres are series of fibrillin rich fibre.
  18. 18. Lens - Anatomy  Histologically lens consists of three major components: 1. Capsule –  It is a thin, transparent, hyaline membrane surrounding the lens  which is thicker over the anterior than the posterior surface.  The lens capsule is thickest at pre-equator regions (14 μ) and  thinnest at the posterior pole (3 μ).
  19. 19.  2. Anterior epithelium.  It is a single layer of cuboidal cells which lies deep to the anterior capsule.  In the equatorial region these cells become columnar, are actively dividing and elongating to form new lens fibres throughout the life.  There is no posterior epithelium, as these cells are used up in filling the central cavity of lens vesicle during development of the lens.
  20. 20.  3. Lens fibres.  The epithelial cells elongate to form lens fibres which have a complicated structural form.  Mature lens fibres are cells which have lost their nuclei.  As the lens fibres are formed throughout the life, these are arranged compactly as nucleus and cortex of the lens
  21. 21.  i. Nucleus.  It is the central part containing the oldest fibres.  It consists of different zones  Which are laid down successively as the development proceeds. In the beam of slit-lamp these are seen as zones of discontinuity.  Depending upon the period of development, the different zones of the lens nucleus include
  22. 22. Embryonic nucleus.  It is the innermost part of nucleus which corresponds to the lens upto the first 3 months of gestation.  It consists of the primary lens fibres which are formed by elongation of the cells of posterior wall of lens vesicle.
  23. 23. Fetal nucleus. It lies around the embryonic nucleus, corresponds to lens from 3 months of gestation till birth. Its fibres meet around sutures which are anteriorly Y- shaped  and posteriorly inverted Y-shaped .  Infantile nucleus corresponds to the lens from birth to puberty, and  Adult nucleus corresponds to the lens fibres formed after puberty to rest of the life.
  24. 24. Lens Cortex Cortex. It is the peripheral part which comprises the youngest lens fibres  It is located peripherally and is composed of secondary fibres formed continuously after sexual maturation. It is further divided into:  Deep cortex  Intermediate cortex  Superficial cortex
  25. 25. Lens Cortex  The region between embryonic and fetal nuclear core and soft cortex i.e. infantile and adult nucleus is sometimes referred to as epinucleus. The region between deep cortex and adult nucleus is sometimes referred to as Perinuclear region.  Lens fibres are held together by interlocking of lateral plasma membranes of adjacent fibres to form ball- and-socket and tongue-and-groove joints.
  26. 26.  4. Suspensory ligaments of lens (Zonules of Zinn).  Also called as ciliary zonules,  these consist essentially of a series of fibres passing from ciliary body to the lens.  These hold the lens in position and  enable the ciliary muscle to act on it
  27. 27.  These fibres are arranged in three groups: i. The fibres arising from pars plana and anterior part of ora serrata pass anteriorly to get inserted  anterior to the equator. ii. The fibres originating from comparatively  anteriorly placed ciliary processes pass posteriorly  to be inserted posterior to the equator. iii. The third group of fibres passes from the summits  of the ciliary processes almost directly inward to  be inserted at the equator
  28. 28. Lens - Crystalline Lens fibres contain high concentrations of crystallins. Crystallins represent the major proteins of the lens (constitute 90% of total protein content of lens). Crystallin has the following constituents: Alpha Beta and, Gamma
  29. 29. Lens - Functions  The lens serves two major functions:  Focusing of visible light rays on the fovea  Preventing damaging ultra-violet radiation from reaching the retina
  30. 30. Lens - Physiology  Lens function is dependent on the metabolism of glucose to produce energy , protein synthesis and a complex antioxidant system. Glutathione is found in high concentration in lens and helps protect its structure from oxidative damage.
  31. 31.  The crystalline lens is a transparent structure playing main role in the focussing mechanism for vision.  Its physiological aspects include :  Lens transparency,  Metabolic activities of the lens, and  Accommodation  Lens transparency  Factors that play significant role in maintaining out standing clarity and transparency of lens are
  32. 32.  Avascularity,  Tightly-packed nature of lens cells,  The arrangement of lens proteins,  Semipermeable character of lens capsule,  Pump mechanism of lens fibre membranes that regulate the electrolyte and water balance in the  lens, maintaining relative dehydration Auto-oxidation and high concentration of reduced  glutathione in the lens maintains the lens proteins  in a reduced state and ensures the integrity of  the cell membrane pump.
  33. 33. Pump leak theory
  34. 34. ACCOMMODATION  As we know that in an emmetropic eye, parallel rays of light coming from infinity are brought to focus on the retina, with accommodation being at rest.
  35. 35. APPLIED ANATOMY  ANOMALIES OF ACCOMMODATION  Anomalies of accommodation are not uncommon.  These include:  (1) Presbyopia,  (2) Insufficiency of accommodation,  (3) Paralysis of accommodation  (4) Spasm of accommodation
  36. 36. Thank You

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