Crystalline Lens

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1. LENS
ANATOMY & PHYSIOLOGY OF LENS
ACCOMMODATIVE APPARATUS &
ITS MECHANISM

2. LAYOUT
oINTRODUCTION
oEMBRYOLOGY
oANATOMY
oPHYSIOLOGY
oACCOMMODATION

3. INTRODUCTION
Asymmetric oblate spheroid
Does not possess nerves, blood
vessels, or connective tissue
Transparent
Crystalline structure
Prolatespheroid Oblate spheroid

4. DEVELOPMENTOF THE LENS
Derived from surface ectoderm
First apparent at about 25 days
of gestation

5. LENS PLACODE :
Appears on 27
th
day of gestation
Area of thickened cells is called
lens plateor lens placode

6. LENS PIT:
Appears at 29
th
day of gestation
Lens placode & adjacent cells of
optic vesicle invaginatesinward
to form lens pit
Also known as Fovea Lentis

7. LENS VESICLE:
Formed at about 33
rd
day of
gestation
Lens pit separates from surface
ectoderm and forms lens vesicle

8. LENS CAPSULE
During process of invagination, the basal lamina comes
to surround lens vesicle
Basal lamina gradually thickens by deposition of
successive layers of basal lamina material to form Lens
Capsule

9. PRIMARY LENS FIBERS AND THE EMBRYONIC NUCLEUS
Posterior cells of lens vesicles rapidly
elongate and obliterate the lumen of
the cavity
By 45
th
day of gestationthe lumen is
completely obliterated and the cells
are called Primary lens fibers
Make up the Embryonic nucleus that
will occupy the central area of lens in
adult life

10. DEVELOPING LENS EPITHELIUM
Cells of anterior lens vesicle form
Lens epithelium

11. SECONDARY LENS FIBERS
Pre-equatorial cells of lens epithelium form the
Secondary lens fibers
Starting from the 7
th
week of gestation

12. Anterior aspect of fibers grow
towards the anterior pole and
posterior aspect grows towards
posterior pole of the lens
Meet on the vertical planes, the
Lens sutures

13. LENS SUTURE AND FETAL NUCLEUS:
These are formed only
during fetal life
Erect Yanteriorly and
inverted Yposteriorly

14. As secondary fibers are added, the sutures
become more complex and dendriform
The secondary lens fibers formed between 2
nd
to
8
th
months of gestationmake up the fetal nucleus
After birth symmetrical branching of sutures
results stellate structure in adult nucleus

15. APPLIED ANATOMY
SUTURAL CATARACT
Opacification of Y-suture of fetal
nucleus

16. FORMATION OF LENS CAPSULE
Lens epithelial & superficial fiber cells continue to
secrete components of basal lamina, which thickens to
become lens capsule

17. TUNICA VASCULOSA LENTIS
Vascular mesenchymal layer
Arises from hyaloid artery
Source of nourishment to lens in fetal period

18. At 1
st
month of gestation, Hyaloid
artery gives rise to small capillaries
which forms the Posterior pupillary
membrane, a network covering
posterior surface of the lens capsule
Fully developed at 9
th
week of
gestation
During human development,
capillaries of tunica vasculosa lentis
and anterior pupillary membrane
regress

19. CLINICAL SIGNIFICANCE OF VASCULOSA LENTIS:
PERSISTENT PUPILLARY MEMBRANE
REMNANT OF THE ANTERIOR PUPILLARY MEMBRANE
Often visible in young healthy patients as pupillary
stands
Minimal visual obscuration

20. MITTENDORF DOT
REMNANT OF THE POSTERIOR
PUPILLARY MEMBRANE
Small, dense white spot located
mostly inferonasally to the posterior
pole of lens
Marks the place where hyaloid artery
comes into contact with the posterior
surfaceof the lens

21. DEVELOPMENTAL ANOMALIES OF THE LENS
SHAPE
1.Lenticonus / Lentiglobus
2.Coloboma
3.Microphakia / Microspherophakia

22. LENTICONUS
Circumscribed conical protrusion of the lenticular pole
Anterior lenticonus is seen in patients with Alport’s syndrome
Posterior lenticonus is seen patients with Lowe’s syndrome

23. LENTIGLOBUS
Hemispherical protrusionof the lens
Localized deformation of the lens surface is spherical
Symptoms include myopia and reduced visual acuity
Appear as an "oil droplet” on retro illumination

24. LENS COLOBOMA
Primary:
Wedge shaped defect or indentation
of the lens in periphery. It mostly
occurs as an isolated anomaly
Secondary:
A flattening or indentation of the lens
periphery caused by lack of ciliary body
or zonular development
These are typically inferior and may be
associated with colobomas of uvea

25. MICROSPHEROPHAKIA
Lens small in diameter and spherical in shape
Visible lens equator
High myopia
Due to faulty development of secondary lens fibers

26. CONGENITAL APHAKIA
Very rare
Complete absence of lens
May be primary or secondary.
PRIMARY:
lens placode fails to develop from the
surface ectoderm
SECONDARY:
more common, developing lens is
spontaneously absorbed

27. STRUCTURAL ANATOMY
DIMENSION
Equatorial diameter
•At birth: 6.5 mm
•In adult: 9-10 mm
Antero posterior/Axial
length/Thickness
•At birth: 3.5 mm
•In adult: 4.75–5 mm
(unaccommodated)
9 mm
5 mm

28. WEIGHT
•at birth: 65-90 mg
•in adult: 255 mg
Increases by rate of 2 mg/year
SURFACES
•Anterior surface:
•Less convex (8-14 mm)
•Anterior pole
•Posterior surface:
•More curved (4.5-7.5 mm)
•Posterior pole
Optical Axis: line joining the two poles

29. REFRACTIVE PROPERTIES
REFRACTIVE INDEX
•Peripheral cortex:1.386
•Central nucleus:1.41
Anterior capsular surface has more R.I than posterior
Depends upon protein concentration and lens fibers
Slightly more than aqueous and vitreous humor
REFRACTIVE POWER
16-17 D
Cornea 1.37
Cornea +43 D
Eye
Eye +60 D

30. EQUATOR
Marginal circumference of lens,
where anterior and posterior
surface meets
Encircled by ciliary processes of
ciliary body and held in position
by zonules laterally

31. ANATOMICAL RELATIONS
Anterior Surface: Behind the
Anterior chamber & Posterior
surface of the iris
Lateral Surface: Posterior
chamber of the eye and to the
zonules through ciliary
processes
~3 mm

32. Posterior Surface: Vitreous which is separated Berger’s
space filled with aqueous and is attached to the
posterior surface in a circular fashion by ligamentum
hyaloideocapsulare (Wiegert’s ligament)

33. STRUCTURE
Histologicallycomposed of 3 structures:
1.Lens Capsule
2.Anterior Lens Epithelium
3.Lens Fibers

34. CAPSULE
Transparent,Hyalinecollagenous membrane
completely envelops the lens
Thickest basement membrane in the body, produced
throughout life
Secreted by (basal part of) lens epithelium anteriorly and
elongating cortical fibers posteriorly
Thickness of anterior capsule increases with age and that
of posterior remains constant

36. No elastic tissue present but highly elastic due
to lamellar or fibrillar arrangement
Capsule is permeable to water, ions and small
molecules and offers barrier to protein
molecule, albumin & Hb

37. ARRANGEMENT OF ZONULAR FIBERS
Zonular fibers arise from the posterior end of
pars plana (~1.5mm from ora serrata)
Zonular complex can be divided into 4 zones
Pars orbicularis :-Passes forward over the pars
plana from its origin
Zonular plexus :-Zonular fibers segments into
Zonular plexus

38. Zonular fork :-Zonular plexus consolidate into
Zonular bundles and bends at right angle to proceed
to lens.
Zonular limbs :-3 in number
Anterior zonular limbs / orbiculo-anterior capsular fibers
Equatorial zonular limbs /cilio-equatorial fibers
Posterior zonular limbs / orbiculo-posterior capsular fibers

39. INSERTION OF THE ZONULAR FIBERS
Anteriorly and posteriorly at peripheryand at equatorof
the lens
The layer of inserting zonular fibers and the related
capsular layer are termed Zonular lamella
Non-elastic
Collectively referred to as the suspensory ligaments of the
lens.

40. ZONULAR LAMELLA
Less compact
Richer in glycosaminoglycans than the rest of the
capsule
The lamella contributes to the zonular adhesive
mechanism
Pericapsular membrane

41. APPLIED ANATOMY
Ectopialentis
Displacement of lens from its normal position
May be congenital, developmental or acquired
May be dislocated or subluxated

42. Subluxation:partially displaced
from normal position but remains
in the pupillary area.
Dislocation: complete
displacement from pupil i.e.
separation of all zonular
attachments

43. Associated with systemic feature
1.Marfan syndrome :-upward & temporal displacement
2.Homocystinuria :-downward and nasal subluxation
3.Weil-Marchesanisyndrome :-forward subluxation

44. LENS EPITHELIUM
Single layered
Deep to anterior lens
capsule
Secretes anterior lens
capsule throughout life
Increased density
toward the periphery.
No corresponding posterior layeris present as the cells are used up in
filling the central cavity of the lens vesicle.

45. 1.Central zone
2.Intermediate/ Tansitionalzone
3.Germinative zone
ZONES OF LENS EPITHELIUM

46. Amount of Cells reduces with age
Do not mitose
Provides well defined cytoskeletondue to proteins like
actin, vimentin and microtubulin
INTERMEDIATE ZONE
Peripheral to central zone
CENTRAL ZONE

47. Most peripheral
Major site of cell differentiation
Highest metabolic capacity
GERMINATIVE ZONE

48. From this region new cells migrate posteriorlyto
become lens fibers
Play the primary role in regulating the water and ion
balance
Germinative zone, unlike the central zone (lies in
pupillary aperture) is protected from the harmful
effects of UV radiation by its location behind the iris

50. LENS FIBERS
Hexagonal in cross-section
Formed constantly at
equator throughout life
from germinative cells

51. Primary lens fibersare formed from the posterior
epithelium during embryogenesis
Secondary lens fibers are formed by
differentiation from germinative cells

52. ELONGATION OF LENS FIBERS
Secondary lens fibers elongates anteriorly and
posteriorly.
Anterior aspectof lens fiber extend anteriorly beneath
the lens epithelium, toward anterior pole of the lens.
Posterior aspectextends posteriorly along the capsule
towards the posterior pole of the lens

53. Reach the sutures,
stop elongating
and their basal
ends detach from
the capsule.

54. Lose all cellular organelles (nuclei, mitochondria,
ribosomes)
Lack independent metabolic activity
Depends upon glycolysis for energy

55. LENS FIBRE ULTRASTRUCTURE
SUPERFICIAL LAYERS
“Ball and Socket” like joints arranged regularly along
the length of the fiber
Mainly important for the movement of the fibers during
accommodation.

56. DEEPER LAYER OF CORTEX AND THE NUCLEUS
Tongue and groove joints
Essential for the continuing transparency of the lensalong
with providing limited degreeof fiber sliding and
flexing of lens structure whole of which is a requirement
of accommodation.
LENS FIBRE ULTRASTRUCTURE
Ball and
socket joints
Tongue and
groove joints

57. Lens Fibers are laid down in concentric layers
•Cortex (outermost)
•Nucleus (innermost)

58. ZONES OF LENS FIBER
NUCLEUS
Central part, containing oldest fibers
Fibers arranged in compact fashion
so harder in consistency
CORTEX
Peripheral part, composed of
recently formed fibers
Fibers loosely arrangedso soft in
consistency
Nucleus
Cortex

59. LAYERS OF NUCLEUS
Embryonic:
Innermost
Primary lens fibers formed in the
lens vesicle during embryogenesis
Fetal:
From 3 month to birth
Infantile:
Birth to puberty
Adult:
Corresponds to adult lens

60. COMPOSITION OF LENS FIBER
LENS FIBRE PROTEINS
1.Insoluble proteini.e albuminoid
2.Soluble proteins are alpha, beta and gamma crystallins
CYTOSKELETAL ELEMENTS
Actin, vimentin, and tubulin
Stabilize the fiber cell membrane.

61. LENS CRYSTALLIN
Two alpha crystallin ‘alpha-A’ and ‘alpha-B’
Alpha crystalline functions in preventing protein
aggregation and precipitation
Reduces the amount of light being scattered

62. SUTURES
Junctions between the apical and
basal end of the cells from the
opposite sides of the lens fibers
ANTERIOR:
Erect Y shaped and formed by
interdigitation of apical cell processes
POSTERIOR:
Inverted Y shaped and formed by
interdigitation of basal cell processes

63. Later on, the growth of the lens suture is irregular
Thus newly formed sutures have dendritic pattern
Increasing geometrical complexity of suture
pattern in adult human lenses results in better
optical properties

64. BIOCHEMISTRY

65. WATER
Low amount of water to maintain the refractive index
Lens dehydration maintained by active sodium pump
Cortex more hydrated than nucleus
PROTEIN
Water soluble (80%) :-crystallin –alpha(32%), beta(55%) and
gamma(1.5%)

66. FUNCTION OF CRYSTALLIN
Refractive function
Change of shape during cell differentiation
Stress-resistant & oxidative properties
Chaperone-like functions
Prevent insolubilization of heat denatured proteins
Facilitate the renaturation of proteins that have
been chemically denaturated

67. Main site –lens epithelium
Main Aims
1.Lens transparency
2.Accommodation
3.Carbohydrate metabolism
4. Regulation of lens electrolyte balance to maintain
normal hydration of the lens
5. Protection of the lens from oxidative damage
LENS PHYSIOLOGY

68. LENS TRANSPARENCY
Normally transmits 80% light energy
Result of:-
1.Single(thin) layer of Epithelial cells
2.Semi permeable lens capsule
3.Highly packed structure of lens fibers(zones of
discontinuity much smaller than the wavelength of
light)

69. 4. Characteristic arrangement of lens protein
5. Pump mechanism of lens fibers(which regulates the
electrolyte and water balance)
6. Avascularity
7. Auto-oxidation (ensuring integrity of membrane
pumps)

70. ACCOMMODATION
Accommodation is a change in refractive state of eye
d/t alternation of curvature of the crystalline lens as a
result of the action of the ciliary muscle on the zonular
fibers
Purpose: Focus and maximize spatial contrast of the
foveal retinal image.

71. ACCOMMODATIVE APPARATUS
Ciliary body and Ciliary muscle fibers
Lens capsule
Zonules

72. CILIARY BODY & CILIARY MUSCLE FIBEES
Forward continuation of choroid at ora serrate
3 types of ciliary muscle fibres
1.Circular Fibers
2.Longitudinal/ Meridional Fibers
3.Radial Fibers
Function :-Slacken the suspensory ligaments of lens
& thus helps in accommodation

73. MECHANISM OF ACCOMMODATION IN HUMAN
Explained by relaxation theory
In unaccommodated state
Ciliary muscle relax
Suspensory ligament is at its greatest tension
Lens takes flattest curves &
Retina is conjugate with far point

74. Ciliary muscle is constricted
Zonules of zinn relaxes
Allows the lens to make a more convex form &
Retina is conjugate with near point
In Accommodated state

75. CHANGES IN OCULAR DIMENSION
➢Decrease in equatorial diameter of the lens (by 0.4 mm from 10
to 9.6mm)
➢Pupil constricts
➢Pupillary margin of iris & ant surface of lens move forward
➢Decrease in radius of curvature of ant. (by 5.5 mm from 11-
5.5mm) and post. lens surface
➢Forward movement of lens (reduced anterior chamber)
➢Increased lenticular thickness (by 0.5 mm from 3.5-4mm)
➢Lens sinks downward
➢Choroid moves forward
➢Optically each of these changes increases refractive power of
the eye i.e. eye accommodates

76. CHANGES IN ACCOMMODATIVE POWER
AT BIRTH: 14-15 D
AT 50 YEARS: 1-2 D
AT 25 YEARS: 7-8 D
Amplitude = 4X4 -(age/4)

77. METABOLISM
Lens requires a continuous supply of energy
(ATP) for :
Active transport of ions & amino acids
Maintenance of lens dehydration
Continuous protein synthesis

78. Source of nutrient
Avascular structure
Takes nutrients from two sources by diffusion
1. Aqueous humour (main source)
2. Vitreous humour

80. APPLIED ANATOMY
CATARACTOGENESIS
Disturbance in transparency of lens
leads to its opacification
Occurrence of an optical discontinuity in
the lens of such magnitude as to cause a
noticeable dispersion of light
May be congenital or acquired

81. ACQUIRED CATARACT
AGE RELATED CATARACT
Commonest type of cataract
Usually above 50 years
Usually bilateral
Multifactorial

82. Nuclear sclerosis
Exagerration of normal ageing
changes
Increased yellowish hue
Cortical cataract
Involves anterior, posterior or
equatorial cortex
Spokes like opacities

83. Subcapsular cataract
Anterior subcapsular
Lies directly under the lens capsule
Fibrous metaplasia of lens epithelium
Posterior subcapsular
Lies in front of posterior capsule
Vacuolated, granular or plaque like

84. REFERENCES

85. THANKYOU