The limbus serves as the junction between the cornea and sclera, facilitating aqueous humor outflow and hosting stem cells essential for corneal epithelium renewal. Limbal epithelial stem cell deficiency can lead to serious corneal issues, necessitating grafting or alternative stem cell therapies for repair. The sclera encases the eyeball, providing structural support and attachment for muscles, and is composed of three layers with vascular and nerve supplies that contribute to its function and sensitivity to inflammation.

3. LIMBUS…
• The limbus forms the border between the transparent cornea and
opaque sclera, contains the pathways of aqueous humour outflow,
and is the site of surgical incisions for cataract and glaucoma

5. Anatomical Limbus: Circumcorneal transitional zone of the
conjunctivocorneal & corneoscleral junction
Conjunctivo-corneal junction:
• Bulbar conjunctiva is firmly adherent to underlying structures
• Substantia propria of the conjunctiva stops here but its epithelium
continues with that of the cornea.
Sclero-corneal junction:
• Transparent corneal lamellae become continuous
• With the oblique, circular and opaque fibres of sclera

12. CONTINUE….
• In the area near limbus, the conjunctiva, tenon’s capsule & the
episcleral tissue are fused into a dense tissue which is strongly
adherent to corneo scleral junction.It is preferred site for obtaining a
firm hold of the eyeball during ocular surgery.
• The limbus is a common site for the occurrence of corneal epithelial
neoplasm.
• The Limbus contains radially oriented fibrovascular ridge known as
the palisades of Vogt that may harbour a stem cell population. The
palisades of Vogt are more common in the superior and inferior
quadrants around the eye

13. CONTINUE…
• Limbal epithelial stem cells reside in the basal layer of the epithelium,
which undulates at the limbus.
• Daughter transient amplifying cells (TACs) divide and migrate towards
the central cornea to replenish the epithelium, which rests on
Bowmans layer .
• The stroma of the limbal epithelial stem cell niche is populated with
fibroblasts and melanocytes and also has a blood supply.

17. • LESC deficiency can occur as a result of primary or acquired insults.
Partial or full LESC deficiency leads to deleterious effects on corneal
wound healing and surface integrity .
• Deficiency can arise following injuries including chemical or thermal
burns and through diseases such as aniridia and Stevens Johnson
syndrome .
• As a result of LESC deficiency conjunctivalisation , neovascularization ,
chronic inflammation, recurrent erosions, ulceration and stromal
scarring can occur causing painful vision loss .

18. • Long term restoration of visual function requires renewal of the
corneal epithelium, through replacement of the stem cell population
has traditionally been achieved by grafting limbal auto- or allografts .
• Recently it has been demonstrated that other stem cell populations
including human embryonic stem cell and hair follicle stem cell can be
driven towards a corneal epithelial-like phenotype.
• These exciting data may lead to alternative therapeutic strategies in
the future for patients blinded by ocular surface disease cause by
failure of LESC function.

21. SCLERA

22. INTRODUCTION
• The sclera forms the posterior opaque 5/6 part of the external fibrous
tunic of the eyeball.
• Its whole outer surface is covered by tenon’s capsule and also by the
bulbar conjunctiva in the anterior part.
• Its inner surface lies in contact with the choroid with a potential
suprachoroidal space in bertween.
• Sclera is thickest posteriorly(1mm) and gradually becomes thin when
traced anteriorly.

24. Special regions of sclera
Scleral sulcus
• It is an indentation(furrow) on the inner surface of the anterior most point
of the sclera near the limbus.
Sclera spur
• It is a circular flang of the anterior most part of the sclera which lie deep to
schlemm’s canal.
• It appears wedge-shaped in section.
Lamina cribrosa
• It is a sieve-like sclera from which the fibres of the optic nerve pass.

25. Scleral apertures(emissaria): Sclera has three sets of apertures
1. Posterior aperture : situated around the optic nerve.
2. Middle apertures: situated 4-7mm posterior to the equator.
3. Anterior aperture: situated 3-4mm away from the limbus

27. Microscopic structure
• Histologically, sclera consist of following three layers:
1. Epicleral tissue
2. Sclera proper
3. Lamina fusca

28. Episcleral tissue
• It is a thin, dense vascularised layer of the connective tissue which
covers the sclera proper.
• Anteriorly it becomes continuous with the tenon’s capsule

30. Sclera proper
• It is an avascular structure which consist of dense bundles of
collagens fibres crossing each other in all direction.
• Variability in collagen fiber diameter, interlacing in bundles of
collagen, and relative deficiency in water-binding substances accounts
for the scleral dull-white color.
• This arrangement makes the sclera opaque in contrast to cornea.
• Mucopolysaccharides are present in the interfibrillar space of the
collagen fibre.
• Few fibroblasts are also present in this layer.

31. Lamina fusca
• It is the innermost part of sclera which blends with suprachoroidal
and supraciliary lamina of the uveal tract.
• It is brownish in colour owing to the presence of pigment cells.

32. Blood supply
• The episclera receives its blood supply from the anterior ciliary arteries,
anterior to the insertions of the rectus muscles and the long and short
posterior ciliary arteries.
Nerve Supply
• The sclera is supplied by the branches from the long ciliary nerves
anteriorly and short ciliary nerves behind the equator. Rich in nerve supply
so causes pain- inflammation, stretching due to oedema and movement of
eye

33. Function
• Protects intraocular components from trauma, light, and mechanical
displacement
• Withstands the considerable expansive force generated by the
intraocular pressure maintaining the shape of the globe
• Provides attachment sites for the extraocular muscles.

34. • Inflammations of sclera
1. Episcleritis (superficial)
2. Scleritis(deep)