Tenon capsule ,Sclera and limbus : subash

anatomy and its applied anatomy of Tenon-capsule, sclera and limbus

1. THE FASCIA BULBI - thin fibrous sheath which envelops the globe from the margin of the cornea to the optic nerve. Has two surfaces: The inner surface :well defined and is in contact with the sclera, connected to it by fine trabeculae . The outer surface : is in contact with the orbital fat posteriorly from which it is separated with difficulty

2. Anteriorly : firmly attached to sclera about 1.5mm posterior to corneoscleral junction Posteriorly : fuses with the meninges around the optic nerve and with the sclera around the exit of optic nerve Inferiorly : thickened to form a sling or hammock which supports the globe as the suspensory ligament of Lockwood where it is pierced by the tendons of extra ocular muscles.

3. MAIN FUNCTION To position and support the globe within the orbital cavit y To permit the actions of extrinsic muscles to produce movement of eyeball .

4. APPLIED ANATOMY OF FASCIA BULBI During enucleation of the eyeball the fascial sheath should be preserved to serve as a socket for the prosthesis Close relationship exists between the suspensory ligament of lockwood and the inferior rectus and the inferior oblique muscle making operations on these muscles very difficult.

5. CONTD… Even after extensive removal of maxilla , eyeball does not sag down because the suspensory ligament is strong enough to provide the eyeball with adequate support from below. Extension of the fascial sheath through the orbital fat to the bony walls of orbital cavity assists the orbital septum in preventing herniation of fat into the lids.

6. EMBRYOLOGY OF SCLERA The human sclera differentiates from neural crest and mesoderm 7 week The majority of the sclera differentiates from neural crest that surrounds the optic cup of Neuroectoderm a small temporal portion of the sclera differentiates from mesoderm

7. SCLERA Forms Posterior five-sixth part of eyeball normally white in adults visible anterior Portion: white of the eye.

8. consists almost entirely of the collagen( chiefly with type 1 and moderately with type 3) within a lesser amount of the ground substance and scanty fibrocytes . Viscoelastic relatively avascular thicker in males than in females

9. Scleral collagen fibrils are highly variable in their diameter, lamellae vary in thickness, irregular with respect to neighbouring lamella water content of the sclera 68 %

10. DIMENSIONS roughly spherical. Coronal diameter: 22-24mm Antero-posterior diameter: 16-17mm at birth : 22.5mm at 3yrs Attains the adult size 22-24mm by the age of 13yrs

11. THICKNESS

12. SPECIAL REGION OF SCLERA Both the internal and external aspects of sclera at the sclerocorneal junction project more anteriorly than the main body of sclera- concave cirumferential groove - Internal scleral sulcus (occupied by trabecular meshwork) Just posterior to the limbus and lying within the sclera is circular running canal called the canal of schlemn .

13. SCLERAL SPUR Circular flang of the anterior most part of sclera lies deep to Schlemm’s canal Meridional fibres of ciliary muscle attached to SS.

14. LAMINA CRIBOSA thin, sieve-like portion of sclera at the base of the optic disc through which optic nerve passes. Concave at intraocular aspect Holes in the network remain relatively aligned with each other providing unobstructed passage for bundle of nerve fibers

15. MICROSCOPIC STRUCTURE Episcleral tissue Scleral proper 3. Lamina fusca

16. INSERTION T he medial rectus: 5.5mm The inferior rectus: 6.5mm The lateral rectus: 6.9mm The superior rectus: 7.7mm The insertion of the superior and the inferior oblique are posterior to the scleral equator .

17. APERTURES Sclera is pierced by two potential openings Anterior scleral foramen : where sclera meets and anatomically converges with cornea Posterior scleral foramen : Provides an exit for the optic nerve

18. EMISSERIA Channels through which vessels and nerves pass through the sclera . Anterior emissari a M iddle emissaria : P osterior emissaria :

19. BLOOD SUPPLY Anteriorly by the anterior cilliary artery. Posteriorly by short ciliary artery Episcleral plexus Underlying choroid

20. NERVE SUPPLY Anterior portion : two long ciliary nerves Posterior portion: many short ciliary nerves

21. APPLIED ANATOMY Profuse sensory innervation of sclera results in dull aching pain associated with inflammations of sclera. The pain is worse during ocular movement Emissaria provides pathway for extraocular spread of intraocular tumors. Most common site for extension is along optic nerve

22. CONT… Scleral rupture following blunt trauma can occur at a number of sites: -in a circumferential arc parallel to the corneal limbus opposite the site of impact, -at the insertion of rectus muscles or at the equator of the globe. -The most common site is the superonasal quadrant near the limbus .

23. CONT… As the scleral is thin the strabismus and retinal detachment surgery require careful placement of the suture. In infantile glaucoma, the viscid slow stretch in response to changes in IOP results in buphthalmic globe .

24. CONT.. Progressive Myopia is characterized by scleral thinning and ocular elongation. Defects in scleral ECM remodeling lead to myopia In glaucoma the raised IOP causes lamina cribrosa to bulge outwards – resultant cupping of disc in chronic glaucoma

25. CONT… change in colour of sclera with age and with disease In elderly - yellowish colour In jaundice - yellow discolouration In osteogenesis imperfecta , Ehlers- Danlos syndrome , Pseudoxanthoma elasticum and other collagen diseases thin and blue

26. EPISCLERITIS Immununologically mediated recurrent inflammation of the tissue that lies between the deep conjunctival stroma and superficial scleral lamellae Presence of deep hyperemia is benign, short-lived not associated with tenderness, ciliary pain or flare and cell in the anterior chamber Caused by allergy to food, airborne allergen.

27. SCLERITIS Immunologically mediated inflammation of the sclera always associated with the secondary inflammation of the episclera deep hyperemia, tenderness, ciliary pain, photophobia and flare and cells in the anterior chamber Causes: auto-immune collagen vascular disease like SLE, Scleroderma, granulomatous diseases like syphillis , tuberculosis, gout. 50% is idiopathic

28. PIGMENTATIONS Nerve loop of Axenfeld : branch of long ciliary nerve accompanying the anterior ciliary artery form a loop in the sclera; often carry some pigments producing blue black spot in superficial sclera.

29. OCULAR MELANOCYTOSIS slate gray patches of scleral and episcleral pigmentations, usually associated with nevus of ota / oculodremal melanocytosis ( ipsilateral hyperpigmentation of the iris, fundus and periocular skin).

30. STAPHYLOMA An ectasia of the outer coats(cornea, or sclera or both) of the eye with an incarceration of the uveal tissue.

31. THE LIMBAL TRANSITION ZONE Junctional zone between the cornea and sclera. 1.5mm wide in horizontal plane and 2mm wide in vertical plane Internal edge; corneal limbus External edge; scleral limbus

32. Scleral limbus Defined by a line perpendicular to the surface passing through the scleral spur. Corneal Limbus demonstrated by the line joining the termination of Bowman’s layer to the termination of Descemet’s membrane

33. AT THE LIMBUS The corneal epithelium becomes continuous with the epithelium of bulbar conjunctiva Bowman's membrane becomes continuous with the lamina propria of the conjunctiva and tenon's capsule. Stroma becomes sclera Descemet's membrane becomes schwalbe's line. Endothelium lines the trabecular meshwork and becomes continuous with the anterior surface of the epithelium Pallisades of Vogt :folds of epithelial cells that run radially into the cornea

34. THE ANATOMICAL LIMBUS The anatomical limbus takes up an arc as it traverses the tissues in an anterior to posterior manner Schwalbe’s line marks the posterior limit to the anatomical limbus .

35. SURGICAL LIMBUS 2mm wide circumcorneal transition zone between the clear cornea and opaque sclera

36. THE CATARACT INCISION & THE SURGICAL LIMBUS Anterior limbal incision - At blue limbal zone -traverses Descemet’s membrane,may cause stripping Clear corneal incision - infront of the anterior limbal line - chances of induced astigmatism and Descemet’s membrane stripping

37. Scleral incision - posterior to the posterior Limbal border -excessive bleeding and hyphaema Posterior limbal incision - at white limbal zone -injures trabecular meshwork Mid- limbal incision - at mid limbal line -corresponds to schwalbe’s line -safest

38. REFERENCES Anthony J Bron, Ramesh C Tripathi, Brenda J Tripathi, Wolff’s Anatomy of the eye and orbit, 8th edition External Disease and Cornea,Basic and Clinical Science Course, American Academy Of Ophthalmology Practical Ophtahlmology , A Manual For Beginning Residents, American Academy of Ophthalmology Snell, Richard s. and Michael A. lemp , Clinical Anatomy of the eye, 2 nd Edition, India:Blackwell science,1998. Jack J kanski, Brad Bowling, Clinical Ophthalmology, 7th edition A.K. Khurana Anatomy and Physiology of eye ( third edition) Internet Resources: www.oculist.com : www.eophtha .com