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EMBRYOLOGY , ANATOMY ,
ANATOMY OF LENS
BY Dr. Rahul
MODERATOR Dr. Monica
Embryology of lens
Formation of crystalline lens begins very early in
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
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
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
As the lens pit continue to invaginate ,the stalk of cells
that connects it to surface ectoderm consticts and
The resultant sphere is called lens vesicle
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
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
These cells are primary lens fibres
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
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
Lens sutures and fetal nucleus
Lens fiber grows anteriorly and posteriorly ,these
fibers meet with each other,this pattern known as
Y shaped are recognizable at about 8 weeks of
An erect Y suture appearing anteriorly and inverted y
Only during fetal life Y sutures formed.
Later on pattern of lens suture s becomes increasingly
At birth lens weighs 90 mg and increases in mass at
rate of 2mg per yr
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
It is fully developed at 9 weeks of gestation disapper
shortly after birth
lens placode in surface ectoderm
invaginates as lens vesicle
supplied by hyaloid artery
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
Its weight varies from 135 mg (0-9 years) to 255 mg
(40-80 years of age).
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).
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.
Lens - Anatomy
Histologically lens consists of three major
1. Capsule –
It is a thin, transparent, hyaline membrane
surrounding the lens
which is thicker over the anterior than the posterior
The lens capsule is thickest at pre-equator regions (14
thinnest at the posterior pole (3 μ).
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.
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
As the lens fibres are formed throughout the life,
these are arranged compactly as nucleus and cortex of
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
Depending upon the period of development, the different
zones of the lens nucleus include
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.
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-
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.
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:
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.
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
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
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:
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
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.
The crystalline lens is a transparent structure playing main
role in the focussing mechanism for vision.
Its physiological aspects include :
Metabolic activities of the lens, and
Factors that play significant role in maintaining out
standing clarity and transparency of lens are
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.
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.
Anomalies of accommodation are not uncommon.
(2) Insufficiency of accommodation,
(3) Paralysis of accommodation
(4) Spasm of accommodation