3. Introduction
• Bi convex structure
• Behind posterior
chamber and pupil
• Cornea and lens are
principle refractive
element of eye
• Divides eye into
anterior and posterior
segments
5. Primary fiber formation
• The thickening of surface ectodermal cells
to form the lens placode (yellow).
• The invagination of the lens placode toward
the developing optic cup (blue). .
• The elongation of posterior lens vesicle
cells as they terminally differentiate to form
primary lens fibers.
6. Secondary fiber formation
Zones Area of anterior
lens
Role
Central zone 80% Not differentiated into fibers
Pre germinative zone 5% Daughter add to the lens epithelial
population
Germinative zone 10% Daughter cells are selected to
terminally differentiate into
additional fibers.(secondary fibers)
Transistional zone 5% Nascent fibers
The lens epithelium- basal layer
7. Fiber elongation
• Lens epithelial cells differentiate into
secondary fibers.
• As these cells migrate posteriorly, their shape
changes from low cuboidal to high columnar
and finally to elongate, crescent fiber.
• However, it is most important to note that the
in addition to a crescent curvature, the ends
of most secondary fibers have additional
curvature in opposite directions but within
growth shells.
8. Fiber elongation
• A view through a lens split along its
anteroposterior or visual axis reveals
concentric growth shells and/or radial cell
columns
• All primary and secondary fibers formed are
retained and must be supported for a
lifetime.
9. • Primary lens fibres—forms emryonic
nucleus
• Secondary lens fibres - includes all other
nucleus
• Lens capsule-produced by anterior
epithelial cells
• Lens zonules—from neuroectoderm in
ciliary area(3rd – 5th month)
10. Lens suture
• Y suture of fetal nucleus
• Star sutures of juvenile and adult nuclei
and cortex
• Sutures and optical lens quality
11. Y suture of the fetal nucleus
• End of fibres latitudinal arc segments
12. Formation of Y sutures during fetal development.
•After the primary fiber mass (dark gold embryonic
nucleus) has been formed, six straight fibers normally
positioned equidistantly around the equator, separate
growth shells into equal sextants composed of S-
shaped fibers.
•The ends of the S-shaped fibers touch and overlap to
form suture branches (blue lines) that extend to
confluence at the poles.
•The end result is an upright Y anterior suture and an
inverted posterior Y suture
13. The three anterior suture branches are normally oriented at 120 longitudinal
degrees to one another to form a Y suture pattern. The three posterior suture
branches are also normally oriented at 120 degrees to one another but because
of opposite-end curvature are offset 60 degrees to the anterior suture branches
to form an inverted Y suture pattern.
Anterior suture
Erect Y suture
Posterior suture
Inverted Y suture
14. STAR SUTURES OF THE JUVENILE AND ADULT
NUCLEI AND CORTEX
Structural elements in the production of a primate
lens six branch star suture formed from birth through
infancy
•At birth there are three Y suture branches.
•In successive growth shells, additional straight fibers
form additional suture branches.
•By the end of the infantile period, 12 straight fibers,
positioned equidistantly around the equator, separate
growth shells into equal groups of S-shaped fibers with
ends that touch and overlap to form a simple star suture.
15. Key structural elements in the production of
discontinuous suture planes in human lenses.
•From birth through infancy no uniform shape
•12 suture branches form “discontinuous” suture planes
throughout the juvenile nucleus.
•18 suture branches constituting the star suture of the
adult nucleus continue to form discontinuous suture.
•the 24 suture branches constituting the complex star
suture of the cortex continue to form discontinuous
suture planes extending from the adult nucleus to the
lens periphery.
16. SUTURES AND LENS OPTICAL
QUALITY
• In the Y suture light rays passing would
repeatedly encounter fiber membrane,
cytoplasm with crystallins, extracellular
space, causing a reduction in lens
sharpness of focus.
• However, as lenses grow and age and
light rays pass through the lens, they
encounter fewer above mentioned
structures.
17. Lens anatomy
• The radius of curvature of anterior surface is
10 mm and that of posterior surface is 6 mm..
• Most fibers are hexagonal in cross section
with two broad and four narrow faces.
• The relative sizes of the cortex
and nucleus in a newborn
(upper) and middle-aged (lower)
human lens..
21. Structure of lens
• Histologicaly composed of three
structures
• Lens capsule
• lens epithelium
• Lens fibers
22.
23. Lens capsule
• Transparent covering that surround the
entire lens.
• Histologically it is a basement membrane.
• The capsule is produced anteriorly by the
lens epithelium and posteriorly by the
elongating fiber cells.
• It is composed of type IV collagen fibers
and sulphated glycosaminoglycans.
• It is highly elastic in nature because of
lamellar or fibrillar arrangement of fibers.
• Lens capsule is thickest near equator and
thinnest at posterior pole.
This extreme thinness of the posterior
capsule makes it more vulnerable for
posterior capsular tear or rent during
cataract surgery.
24. Lens epithelium
• Simple cuboidal epithelium and is
found only in the anterior surface of the
lens.
• secrete the anterior lens capsule
throughout the life.
• Near the equator it becomes columnar
• There is no posterior lens epithelium
because the cells originally located
there have elongated into primary
fibers of the lens
25. Lens fibers
• Transitional zone cells continue to
elongate and differentiate, they turn
meridionally
• The apical end of these cells pass
anteriorly towards the anterior pole and
the basal end are pushed posteriorly
towards the posterior pole.
• New superficial lens fibers are added in
a concentrically arranged lamina, like
the layers of an onion.
26. Zones of lens
• Nucleus occupies 84% of the lens
and cortex occupies 16%.
• The nucleus is further subdivided
into embryonic, fetal, infantile, and
adult nuclei.
• Epinucleus is formed by the zone
between foetal nucleus and cortex.
Hydroseparations
Hydrodissection is the
separation of lens from its
capsule whereas
hydrodelineation is
achieved by injecting fluid
between epinucleus and
nucleus.
27. Lens cortex
• A cortex can be defined as the outer part
or external layers of an internal organ
• The initial growth shells of secondary
fibers comprise the initial external layers of
the lens and are, thus, the original cortical
fibers.
28. Lens nucleus
• The embryonic nucleus is comprised solely of
primary fibers.
• The fetal nucleus is comprised of all the
secondary fibers formed until birth.
• The fibers formed after birth and through
sexual maturation are juvenile nuclear fibers.
• The adult lens nucleus is comprised of all the
secondary fibers formed after sexual
maturation minus the fibers of the cortex.
29. Lens cortex and nucleus
• A normal adult human lens
• The human adult lens nucleus has a uniform
yellow coloration clearly distinct from the
colorless cortex.
• Based on the diameter of the chromatic region,
the average thickness of the cortex in adult
human lenses (age range 49 to 73 years) is
1.13 mm ± 0.15 mm.
• The thickness of the lens cortex does not
appear to change with age.
30. Zonules of lens
• Zonules or suspensory ligament of
lens are a group of radially
arranged,thread like fibres which
helps the lens to held in position
31. Cilliary zonules
Pars orbicularis-
part over pars plana
Zonular plexus- part in
between cilliary process
and pars plicata
Zonular fork- part which
consolidates to zonular
bundles
Zonular limbs
Anterior zonular limb
Equatorial zonular limb
Posterior zonular limb
33. Accomodation
• The eye has the capacity to adjust its focus from distance to
near objects because of the ability of the lens to change
shape, a phenomenon known as accommodation.
• Zonular fibers on the lens capsule is controlled by the action
of the parasympathetically innervated ciliary muscle.
• When cilliary muscles contracts, relaxation of zonular tension
occurs. The lens then assumes a more spherical shape,
resulting in increased dioptric power which helps to bring
nearer objects into focus.
• Ciliary muscle relaxation causes the zonular tension to
increase. As a result, lens flattens, which helps in bringing
more distant objects into view.
34. Presbyopia- at the age of 40-50 yrs, the elasticity of the lens diminishes. The
contractility of the ciliary muscle also diminishes due to the structural changes in the
muscle. As a result lens fails to change its shape sufficiently during accommodation.
35. LENS CELL HOMEOSTASIS
• The size of any tissue cell population is
determined by the cell birth rate(KB) and
the cell loss rate(KL).
• The lens grows throughout life because
KB is greater than KL.
• From fetal development, and continuing
throughout life, the lens produces more
cortical fibers that eventually become
nuclear fibers.
36. LENS EPITHELIAL CELL
HOMEOSTASIS
• GZ KB is greater than GZ KL, and, therefore,
the GZ is a growing cell population
throughout life.
• Consequently, although CZ KB is greater
than CZ KL from birth through adulthood, it is
less from adulthood through old age
• Although the CZ is a growing cell population
throughout adulthood, it is a regressing cell
population for the rest of life.
37. LENS EPITHELIAL CELL
APOPTOSIS
• The lens epithelium eliminates some cells
by apoptosis throughout life.
• The increasingly large and prominent
lysosomal bodies likely represent
breakdown of apoptotic cells and
fragments.
42. References
• Fundamentals and principles of
Ophthalmology,section 2,2014-2015, American
Academy of Ophthalmology
• Duane's Foundations of Clinical Ophthalmology,
Foundation volume 1
• Jack J Kanski, Brad Bowling, Clinical
Ophthalmology, seventh edition 2011
• M.J. Roper- Hall, Stallard’s Eye Surgery, Seventh
Edition, 1989
• Parsons’ Diseases of the Eye, Twentieth Edition
2007
• Internet eophtha
