1. ANATOMY OF THE
LENS

2. LENS EMBROLOGY
 The development of the eyeball starts around
day 22 of gestation and it is around 2mm in
length.

3.  First, a linear thickening develops on either
side of the neural plate which is going to form
the prosencephalon
 It becomes depressed to form the optic
sulcus.
 Walls of prosencephalon overlying the sulcus
bulge out to form the optic vesicle
 Proximal part of the optic vesicle becomes
constricted to form the optic stalk

5.  Optic vesicle grows laterally and comes in
relation with the surface ectoderm
 At 27th day the overlying surface ectoderm
becomes thickened to form the lens placode
 It slowly sinks below the surface and is
converted into lens vesicle
 Seperates from the surface at 33rd day.

8.  Simultaneously, the optic vesicle gets
converted into optic cup due to differential
growth of its margins
 The optic cup surrounds the upper and the
lateral sides of the lens
 It is deficient in the inferior part known as the
choroidal or fetal fissure. This closes by 6th
week. Failure to fuse leads to typical
colobomas.

10.  The neural tube is surrounded by
mesenchyme which condenses to form the
meninges
 The mesenchyme around the optic vesicles
forms 2 layers-
 Superficial fibrous layer- sclera and cornea
 Deep vascular layer- uvea
 Part of the inner vascular layer is carried into
the cup through the fissure. When fissure
closes, it forms the hyaloid vessels

11.  The hyaloid vessels suppy the lens in the
fetus due to which it grows rapidly.
 Later the hyaloid vessels disintegrate and the
remains forms the central retinal artery and
vein. The lens derives its nutrtion then by
diffusion from the aqeous humor and vitreous
humor.

14. ANATOMY OF THE LENS
 Lens is a tranparent, avascular, biconvex
crystalline structure placed between the iris
and vitreous in the patellar fossa

15.  It has 2 surfaces- anterior surface and posterior
surface.
 These 2 surfaces meet at the equator.
 The centre of the anterior and posterior surfaces
are known as anterior and posterior pole
 The posterior surface is attached to the vitreous
by Wiegert’s ligament.
 Between the lens capsule and the hyaloid face is
a small cavity k.a. retrolental space or berger’s
space.

16. DIMENSIONS--
1. Equatorial diameter- 6.5 mm at birth, 10 mm
in adults
2. AP diameter- 3.5 mm to 5mm
3. Radius of anterior surface- 10mm
4. Radius of posterior surface- 6 mm
5. Wieght- 150 mg- 250 mg

17.  Refractive index- 1.38 ( cortex)
1.42 ( nucleus)
 Refractive power- 16-17 D
 Accomodative power- 14-16 D at birth
7-8 D at 25 yrs
1-2 D at 50 yrs

18. STRUCTURE OF LENS

19. Lens capsule
 It is a thin , transparent elastic membrane which
surrounds lens completely
 Secreted by basal cells of anterior lens epithelium
and basal area of elongating fibres posteriorly.
 Thicker anteriorly than posteriorly
 Thicker at the equator than the poles, thinnest at
the posterior poles

20.  It is made up of type 4 collagen and 10%
glycosaminoglycans

21. Anterior lens epithelium
 Single layer of cuboidal nucleated epithelial
cells.
 Cells contain all the organelles found in a
normal epithelial cell since all the metabolic,
synthetic and transport processes of lens
occur in this layer

22. 3 zones
 Central- cuboidal cells which reduce with
age. Do not mitose normally.
Can undergo mitosis in response to injury like
in uveitis.
Metaplasia of these cells into spindle shaped
myofibroblast like cells can lead to ASC- eg.
Shield cataract in atopic dermatitis,
Glaucomflecken after ACG

23. Intermediate zone
 Smaller and more cylindrical.
 Undergo mitosis occasionally
Germinative zone
 Columnar cells located pre- equatorially.
Actively dividing to form new cells which
migrate posteriorly to become lens fibres.
 Extremely susceptible to radiation
 Dysplasia can lead to PSC in radiation
exposure, myotonic dystrophy and NF-2.

24. Lens fibres
 Form the main bulk of the lens. They are long
thin transparent cells firmly packed with
diameter of 4-7 micron and length upto
12mm
 The cells of the newly formed fibres contain
all the organelles and as the fibres mature the
nucleas disappears.

25.  The cells are linked by gap junctions and
interdigitations that look like ball and socket.
These are fewer in the superficial fibres.

26. FORMATION OF LENS FIBRES
 EARLY LENS VESICLE-
consists of a single
layer of cells covered
by a basal lamina.
 LATE LENS VESICLE-
cells of posterior wall
elongate and get filled
with crystallins which
make them
transparent

27.  EMBRYONIC NUCLEUS-
the apices of these cells grow
towards anterior lens epithelium.
These are PRIMARY LENS FIBRES.
 The nuclei of these cells are
present anteriorly forming nuclear
bow.
 When these cells become attached
to the anterior lens epithelium the
nuclei of the cells disappears.
These fibres are formed upto 3
months of gestation.

28. LAYERS OF LENS NUCLEUS
1. EMBRYONIC NUCLEUS- formed by the
primary lens fibres upto 3rd month of
gestation
2. FETAL NUCLEUS- 3rd month to 8th month
3. INFANTILE NUCLEUS- 8TH month till
puberty
4. ADULT NUCLEUS- after puberty

29.  Primary lens fibres forms the embryonic
nucleus.
 Rest of the nuclei are formed from the
secondary lens fibres. These are the fibres
formed from the anterior epithelium
throughout life .

30.  Initially the fibres of
the fetal nucleas reach
both the anterior and
posterior pole.
 Later they are not able
to extend all the way
and instead meet at
radiating lines which
appear as an erect Y
anteriorly and inverted
Y posteriorly

33.  Later the fibres grow
asymmetrically giving
a complicated dendritic
pattern in the infantile
and adult nucleus

34.  The most newly formed (youngest) lens fibres
are present most peripherally outside the
adult nucleus.
 These form the cortex of the lens.

35. Layers of lens on slit lamp

36. Surgical anatomy