The document discusses the embryology, anatomy, physiology and applied anatomy of the lens. It begins by describing the early embryonic development of the lens, including the formation of the lens vesicle from surface ectoderm. It then details the anatomy of the adult lens, including its layers of capsule, epithelium and fibers which make up the nucleus and cortex. The physiology section covers lens transparency, metabolism and accommodation. Finally, it briefly mentions some anatomical anomalies of accommodation such as presbyopia and paralysis.

1. EMBRYOLOGY , ANATOMY ,
PHYSIOLOGY, APPLIED
ANATOMY OF LENS
BY Dr. Rahul
MODERATOR Dr. Monica

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.

4. 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

7.  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

9.  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

10.  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

12. 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

13. Y-shaped sutures of the fetal
nuclear fibres

16. 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

18. Congenital anomalies
 Congenital aphakia
 Lenticonus and lentiglobus
 Lens coloboma
 Mittendorf dot
 Epicapsular star
 Peters anomaly

19. POSTERIOR Lenticonus

20. Lens coloboma

21. Epicapsular star

22. Lens Development
lens placode in surface ectoderm
invaginates as lens vesicle
supplied by hyaloid artery

23. 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).

24.  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).

26.  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.

27. 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).

29.  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.

30.  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

31.  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

32. 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.

33. 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.

34. 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

35. 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.

36.  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

37.  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

40. 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

42. 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

43. 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.

44.  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

45.  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.

46. Pump leak theory

47. 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.

50. 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

51. Thank You