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THE SCLERA

  • This is also known as:
  • Fibrous
  • Outercoat
  • White of the eye
  • Greek – scleros
  • hard
  • The Sclera is continuous with:
  • Dura matter
  • Cornea
  • Origin: Mesoderm

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  • The sclera consist of the:
  • Posterior 5/6 of the outercoat
  • Cornea – consist of the anterior 1/6 of the outercoat

CHARACTERISTICS

  • Opaque
  • Dense collagen
  • Interspersed with elastic fibres
  • Thinnest at the equator and where it is pierced by the recti muscle.
  • Weakest at lamina cribrosa (sieve like).

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  • COVERINGS:
  • Richly vascular episclera
  • Fascia Bulbi (Tenon Capsule)
  • The conjunctiva
  • If a sustained increase of IOP occurs POAG, the lamina cribrosa:
  • yields
  • Bulges cupping (posteriorly at disc)

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LAYERS OF SCLERA

  • Episclera
  • Scleral
  • Lamina fusca

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EPISCLERA

  • Superficial aspect of sclera
  • Bundles of collagen circumferentially arranged
  • Rich blood supply anteriorly
  • Thickness to the rectus muscle insertions and becomes progressively thinner towards the back of the eye.

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SCLERA STROMA

  • Bundles of collagen intermingled with fibroblasts, melanocytes, elastic fibres, proteoglycans and glycoproteins.
  • Variability in collagen fibres diameter, interlacing in bundles of collagen, and relative, deficiency in water – binding substances

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accounts for the sclera dull – white colour.

  • The sclera stroma derives it’s nutrition from the episclera and choroidal vascular network
  • Anterior to the insertion of the recti muscle is the anterior ciliary arteries which forms dense episclera plexus.

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  • These vessels become congested in ciliary injection
  • Small branches of the posterior ciliary arteries supply the sclera stroma posterior to the recti muscle

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LAMINA FUSCA

  • Brown colour due to the melanocytes
  • Grooves for the passage of ciliary vessels, nerves (emissary canals)
  • Attached to the choroid by fine collagen fibres

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BLOOD SUPPLY

  • Episclera – anterior and posterior ciliary arteries
  • Sclera stroma:
  • Relatively a vasculature structure

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VENOUS DRAINAGE

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  • Episclera/collecting vein
  • Anterior ciliary veins
  • Vortex veins

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NERVE SUPPLY

  • Rich in nerve supply
  • Anterior sclera:
  • Long posterior ciliary nerves
  • Posterior sclera:
  • Short posterior ciliary nerves
  • Pain-
  • Inflammation, streching due to oedema and movement of the eye.

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NB: The sclera is white because of:

  • Variable diameter
  • Irregular arrangement of the collagen fibres of the stroma
  • Because of the scathering of all wave length of light by dense irregular bundles of collagen in the sclera

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