Sclera PDF

Sclera Karen Gil MD, MHSN. Sclera Development • Begins in week 7 • Develop from the periocular mesenchymal cells (a derivate of neural crest cells) • Third month extends in the posterior pole to form the lamina cribosa Sclera • Forms posterior 5/6 • Protective connective tissue coat of the globe...

Sclera Karen Gil MD, MHSN. Sclera Development • Begins in week 7 • Develop from the periocular mesenchymal cells (a derivate of neural crest cells) • Third month extends in the posterior pole to form the lamina cribosa Sclera • Forms posterior 5/6 • Protective connective tissue coat of the globe • Maintains the shape of the globe • Provides an attachment to EOM insertions • Composed of – Episclera – Stroma – Inner lamina fusca Scleral Layers • Episclera • Scleral Stroma • Lamina Fusca Sclera • Thickness varies • EOM rectal muscles insertion is the thinnest area of the sclera 0.3mm • Posteriorly has the lamina cribosa that is the weakest area • His thickest area is at the posterior pole of 1.0 mm Episclera • Loose, vascularized connective tissue layer • Outer to the sclera • Larger episcleral vessels are visible through the conjunctiva • Branches of the anterior ciliary arteries form a capillary network in the episclera just anterior to the rectus muscle insertions and surrounding peripheral cornea • Attached to the Tenon’s capsule • Thinner at the back of the eye Sclera • Tick, dense connective tissue layer • Continuous with the corneal stroma • Collagen fibers type – 80% type I – 5% type III – minor amounts type V and VI • Collagen fibrils arranged in irregular bundles that branch and interlace (25 to 230 nm) • Fibrils run parallel to the surface inner regions run in all directions (give strength) FIGURE 1-17. (A) Schematic diagram of the isolated sclera and structures that blend with it (muscle tendons and optic nerve dura) or traverse its substance. (B) The scleral layers. (C) The pattern of orientation of the collagen bundles in the scleral stroma in relation to the extraocular muscle tendinous insertions. (D) Collagen bundles in sclera. Original magnification: D, × 7000 (Part D courtesy of Dr A. Thale, from Thale and Tillmann, 1993.) Sclera Sclera • Stromal Ground surface is similar to the cornea but contains fewer fibroblasts and GAGs • Innermost aspect merges with the choroidal tissue (suprachoroid layer) Scleral Spur • Circular oriented band of collagen bundles • Ring shape • Posterior edge blend with oblique scleral fibers • Posterior scleral spur is the origin of the longitudinal ciliary muscle fibers • Most of the trabecular meshwork sheets attach to its anterior aspect Scleral Opacity • Depends: – number of GAGs – Amount of water – Size and distribution of the collagen fibrils • Contains ¼ amount of GAGs in the cornea, so sclera is more dehydrated (68%) Scleral color • White in healthy • Newborn has a bluish tint in more transparent and uvea shows through • Connective tissue diseases appear blue due to scleral thinning • Yellow – presence of fatty deposits (age) – Liver disease (build up metabolic wastes) Scleral foraminas • Anterior scleral foramen – area occupied by the Cornea • Posterior scleral foramen – Optic nerve passes through – Bridged by a network of scleral tissue called Lamina cribosa (weakest area of sclera) Scleral Canals • Canals carry nerves and vessels(possible routes by which diseases enter o exit the eye) • Posterior apertures – located around the posterior scleral foramen – Passage for the posterior ciliary arteries and nerves Scleral Canals • Middle apertures – 4mm posterior to the equator – Carry the vortex veins • Anterior apertures – Near limbus at the muscle insertions – Passage for the anterior ciliary vessels (branches muscular arteries) Scleral Blood Supply • Minimal blood supply • Number of vessels pass through the sclera • But the sclera is considered avascular – no contains capillary bed • Nourishment is furnished by – Small branches form • the episcleral (anterior ciliary arteries branches) • choroidal vessels (short posterior ciliary arteries branches) • And branches of the long posterior ciliary arteries Scleral Blood Supply • Episcleral Plexus – Superficial – Deep Scleral Innervation • Branches of the short cilliary nerves supply sensory innervation to the posterior sclera • Medial and anterior sclera by branches of the long ciliary nerves Clinical Application • Epiescleritis – Episcleral network become congested – benign inflammatory condition generally of unknown cause – Approximately 30% of cases have been associated with collagen diseases, herpes zoster, gout, syphilis, erythema nodosum, etc. Episcleritis vs Scleritis Clinical Application • Scleritis – is a potentially destructive inflammatory process that may be the presenting sign of severe systemic disease – endogenous origin – leading to granulomatous inflammation of the scleral collagen or vasculitis involving the superficial and deep vessels – Associated systemic diseases: – connective tissue disorders (polyarticular rheumatoid arthritis, ankylosing spondylitis, Reiters' disease, Wegener's granulomatosis) – microbial infection (herpes zoster ophthalmicus, syphilis, tuberculosis, Pseudomonas) – other metabolic conditions • gout, erythema nodosum Clinical Application • Scleral ectasia – Progression of myopia caused by axial elongation in high myopic eye – scleral thinning – Posterior pole is the most affected – Sclera thins and the tissue bulge outward causing scleral ectasia