This document provides information on the embryology, anatomy, and physiology of the lens. It discusses the developmental stages of the lens from the lens placode to the formation of the lens vesicle and fibers. The anatomy sections describe the layers and structures of the lens including the capsule, epithelium, fibers that make up the nucleus and cortex. The physiology section explains how the lens maintains transparency and focuses light through accommodation using active transport mechanisms and crystalline proteins. It also discusses metabolic pathways and anomalies that can affect accommodation.

1. EMBRYOLOGY ,
ANATOMY and
PHYSIOLOGY OF LENS
By Dr.Kaushik DS
Moderator :Dr.Mohan kumar

2. EMBRYOLOGY OF LENS
Age in days Developmental events
2 Embryo is at two-cell stage
3 Morula is formed
4 Blastocyst is formed
8 Bilaminar disc is formed
14 Procordal plate and
primitive streak is seen
16 Intra-embryonic mesoderm
is formed /disc is now three
layered
QUICK RECAP OF
EVENTS

3. Age in days Developmental events
17 Notochord process
appears. Heart tube is seen
in cardiogenic area
19 Intra-embryonic mesoderm
is being formed
21 Neural groove is seen.
23 Closure of the neural tube
is seen

4. DEVELOPMENT OF LENS
LENS PLACODE AND
VESICLE
• 25 days of gestation, 2 lateral out
pouching( optic vesicles) forms from
forebrain.
• Optic vesicles enlarge, become
closely apposed to surface ectoderm.
• Cell surface ectoderm that overlies
optic vesicles become columnar at
about 27 day of gestation.
• The area of thickened cells of
surface ectoderm, is called lens
plate or lens placode.

5. • Initially the lens placode remains attached to
the surface ectoderm of the lens stalk
• The vesical sinks into the orifice of the cup
and zone of extreme attenuation and necrosis
develops in the lens stalk.
• By about 33 days of gestation , the separation
is complete and spherical lens vesicle,
approximately 0.2mm in diameter, comes to
lie inside the eye.

6. • The apices of the cuboidal cells are directed
towards the central cavity of the lens vesicle,
• basal surface is outwards and applied to the
original basal lamina that envelops the vesicle
completely.
• With continued synthesis and secretion by the
lens cells the basal lamina thickness and forms
the lens capsule.

7. • Lens vesicle closes.The rate of DNA synthesis of the cells subjacent to the
neutral retina decreases and their content of cytoplasmic organelles
reduces.
• At the same time they begin to synthesize crystalline
• Cells increase in length , extends towards the anterior surface of the lens
vesicle, its lumen is obliterated by 45 days of gestation.

8. • These primary lens fibers attach firmly to the
apical surface of the anterior lens epithelial cells,
through fascia adherens tight junctions.
• Cell nuclei eventually disintegrate and disappear
• At about 7 week of gestation, the lens epithelium
in the area of equator begin to multiply and
elongate rapidly and forms secondary lens fibers.

9. THE LENS BOW
• The epithelial cells in the pre-equatorial
region retain their mitotic and proliferative
activity throughout life.
• The secondary lens fibers formed are
displaced inwards, they elongate axially
towards 2 poles, encircling and covering the
primary lens fibers.
• The nuclei of the newly formed fibers,
migrate progressively towards the anterior
lens surface and , on sectional view, give
rise to the distinctive configuration known
as the lens bow.

10. • With successive internalization of fibers and
consequent increase in lens volume, new lens
fibers can no longer extend from one pole to
other.
• They meet at radiating lines or sutures that
appear as an erect Y anteriorly and and inverted
Y posteriorly.
• Y sutures , 1st seen at about 35mm stage( aprox
8.5weeks) persists through the entire thickness
of the fetal nucleus, and remain throughout life
as a hallmark of lens development.
• In the infantile and adult nucleus the sutures
become more complex.

11. CHANGES IN LENS SHAPE
• Initially its elongated in anterior posterior diameter.
• 18 to 22 mm stage its spherical
• 26mm stage secondary lens fibers appear and lens becomes
wider at equatorial diameter.
• At birth lens is almost spheroidal being slightly wider at the
equatorial plane.
• Factors that govern these changes are unknown partly
related to zonular traction and dehydration of lens which
starts inutero.

12. ZONULAR FIBRILS
• zonular fibrils are synthesized by ciliary epithelial cells,
and zonules increases in number, strength and
coarseness.
• By 5th month the zonules have reaches the lens and
merge with both the anterior and posterior capsule.

13. TUNICA VASCULOSA LENTIS
 As lens develops, nutritive support structure,the tunica vasculosa lentis from around it.
 At about 1 month of gestation , hyloid artery gives rise to small capillaries that from
anastomotic net covering posterior aspect.
 These small capillaries grows towards equator of lens where they anastasomose with
choroidal veins and form capsulopupillary portion of tunica vasculosa lentis
 Branches of long ciliary arteries anastomose with branches of capsulopupillary portion to
form anterior vascular capsule
 It is fully developed at 9 weeks of gestation disappear shortly after birth

15. CONGENITAL ANOMALIES
 Congenital aphakia
 Lenticonus and lentiglobus
 Lens coloboma
 Mittendorf dot
 Peters anomaly
 Marfans syndrome

16. CONGENITAL
APHAKIA
LENTI CONUS
bulging of the lens capsule and the underlying cortex.
waardenburg syndrome
Lowe syndrome

17. LENS COLOBOMA
Coloboma of the lens is characterized by notching of the equator of the
lens. The cause of the condition is faulty development of the zonule

18. MITTENDORF DOT
Involutional defect of the anterior
terminus of anterior hyaloid artery.
PETERS ANOMALY
Development of the anterior segment is
abnormal, leading to incomplete separation
of the cornea from the iris or the lens

19. MARFANS SYNDROME

20. ANATOMY OF LENS
• The lens is 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 than
posterior surface.

21.  Its diameter is 9-10mm and thickness varies with age from 3.5mm(at
birth) to 5mm(at extreme if age)
 Its weight varies from 135mg(0-9 years) to 255mg(40-80 years)

22.  It has got two surfaces
 The anterior surface is less convex(radius of curvature 10mm) than the posterior (radius of
curvature 6mm)
 These two surfaces meet at the equtor
 Its refractive index is 1.39 and total power is 15-16D
 The accommodative power of lens varies with age, 14-16D(at birth), 7-8D(at 25 years of age)
and 1-2 D( at 50 years of age)

23.  Capsule
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 region and
thinnest at the pole.
 Anterior epithelium
It is a single layer of cuboidal cells which lies deep to anterior capsule.
In the equatorial region these cells become columnar , are actively dividing and elongating
to form new lens fibers 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 lens.

24. Lens fibres
 The epithelial cells elongate to form lens fibres which may 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

25.  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 .

26. BIOMICROSOPIC
STRATIFICATION OF LENS
• Capsule
• Superficial cortex –
3 zones-
C1α,C1β,C2
• Deep Cortex- C3
and C4
• Nucleus

27. EMBRYONIC NUCLEUS
 It is the inner most part of nucleus which corresponds to the lens upon
the first 3 months of gestation.
 It consists of primary lens fibers which are formed by elongation of
cells of posterior walls of lens vesicles.
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 and rest of the life.

28. 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
 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.

29. Suspensory ligaments of lens(zonules of zinn)
 Also called as ciliary zonules
 These consist essentially of series of
fibres passing from ciliary body to lens
 These hold the lens in position and
 enable the ciliary muscle to act on it

30. Zonular fibres are arranged in 3 groups
 The fibres arisisng from pars plana and anterior part of ora serrata
pass anteriorly to get inserted anterior to equator.
 The fibres originating from comparatively anteriorly placed ciliary
process pass posteriorly to be inserted posterior to the equator.
 The third group of fibres pass from the summits of the ciliary process
almost directly inward to be inserted at the equator.

31. LENS PHYSIOLOGY
Lens function is dependent on the metabolism of glucose to produce
energy, protein synthesis and complex antioxidant system. Glutathione is
found in high concentration in lens and helps protect its structure form
oxidative damage.
Biochemical components of lens
 Lens water-65%
 Protein- 34%
 Lipids
 Carbohydrates and derivatives(ascorbic acid, glutathione)
 Amino acids

32. Lens proteins
Water soluble
(intracellular proteins)
Water insoluble
Alpha crystalline
Beta crystalline
Urea soluble
(most cytoskeletal
proteins)
Urea insoluble
(most lens fiber
membrane
protein; includes
major intrinsic
protein(MIPS)
Gamma
crystalline

33. LENS- CRYSTALLINE
 Lens fibres contain high concentrations of crystalline.
 Crystallins represent the major proteins of the lens
 (constitute 90% of the total protein content of lens)
 The concentration of gamma crystallins in the lens increase steadily throughout fetal
life and reaches 23% of the total protein just before birth. Its synthesis ceases just
before birth.
 It accounts for greater transparency of most of the central region of the lens.

34. FUNCTION OF LENS
 The crystalline lens is transparent structure playing main role in the
focusing mechanism for vision,
 Its physical aspects include
Lens transparency
Metabolic activities of lens, and
Accommodation

35. LENS TRANSPARENCY
Factors that play significant role in maintaining out standing clarity and
transparency of lens are
 Avascularity
 Tightly-packed nature of lens cells,
 Single layer of epithelial cells which is not thick
 The arrangement of lens proteins
 Semipermeable character of lens capsule,
 Pump mechanism of lens fibre membrane that regulate the
electrolyte and water balance in the lens, maintain relative
dehydration of lens.
 Glutathione in the lens maintains the lens proteins ,in a reduced
state and ensures the integrity of the cell membrane pump.

36. METABOLIC ACTIVITIES OF LENS
Glucose from the aqueous and vitreous diffuses into the lens and is
rapidly metabolized through four main pathways.
1.Anaerobic glycolysis
2.Krebs cycle
3.Hexose monophosphate shunt
4.Sorbital pathway

38. OIL DROP CATARACT
(GALACTOSEMIA )
SNOW FLAKE
CATARACT(DM)

39. PERMEABILITY AND TRANSPORT
MECHANISMS OF LENS
 Active transport mechanism
Amino acid,potassium,taurine,inositol and extrusion of sodium.
 Passive exchange
Water, ions and waste products of metabolism

40. PUMP–LEAK THEORY
 The combination of active transport and membrane permeability is
often referred to as the pump–leak system of the lens .
 According to the pump–leak theory, potassium and various other
molecules, such as amino acids, are actively transported into the lens
anteriorly via the epithelium.
 They then passively diffuse out with the concentration gradient
through the back of the lens, where there are no active-transport
mechanisms.

41. The pump–leak hypothesis of pathways of solute
movement in the lens. The major site of active-transport
mechanisms is the anterior epithelium, whereas passive
diffusion occurs over both surfaces of the lens.

42. ACCOMMODATION
 In an emmetropic eye , parallel rays of light coming from infinity are
brought to focus on the retina, with accommodation being at rest.

43. ANOMALIES OF ACCOMMODATION
 Presbyopia
 Insufficiency of accommodation
 Paralysis of accommodation
 Spasm of accommodation

44.  Presbyopia is when your eyes gradually lose the ability to see things clearly up
close . After age 40, the lens becomes more rigid. It cannot change shape as
easily. This makes it harder to read, thread a needle, or do other close-up tasks.

45.  Accommodative insufficiency (AI) involves the inability of the eye to focus properly on
an object. In this condition, amplitude of accommodation of a person is lesser compared
to physiological limits for his age.
 In paralysis of accommodation, amplitude of accommodation is either markedly
reduced or completely absent (cycloplegia). It may occur due to ciliary muscle paralysis
or oculomotor nerve paralysis. Parasypatholytic drugs like atropine will also cause
paralysis of accommodation.
 Spasm of accommodation refers to prolonged contraction of the ciliary muscle, most
commonly causing pseudo myopia to varying degrees in both eyes by keeping the lens in
a state of short sightedness.

46. BIBLIOGRAPHY
 Wolff’s Anatomy of the eye and the orbit 8th edition
 Anatomy And Physiology Of Eye by Khurana AK 3rd Edition
 Jakobic’s principle and practice of ophthalmology 3rd edition volume 1
 American academy of ophthalmology (https://www.aao.org/Assets/71992e38-
b728-468b-b862-179fe92be214/637153832340430000/l10-pdf?inline=1)