2 anatomy(Ant.segment-2) .pptx
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The limbus is the transition zone between the cornea and sclera that provides some nourishment to the peripheral cornea. It is also the site of the aqueous humor drainage system. The sclera is a collagenous and relatively avascular outer layer of the eye. The lacrimal gland and accessory glands including glands of Wolfring, Zeis, and Meibomian glands all contribute to tear production. The tear film consists of an inner mucous layer, middle aqueous layer, and outer lipid layer that is spread across the eye by blinking. Tears drain from the medial canthus aided by the scissor-like closing motion of the eyelids.
2 anatomy(Ant.segment-2) .pptx
- 1. Contact Lens Anatomy of Anterior Segment of the Eye -II
- 2. LIMBUS Transition zone between cornea and conjunctiva/sclera An anatomical reference for surgical procedures, bio microscopy and contact lens fitting.
- 3. 1mm Depth 1.5 Width (horizontal) 2.5 Width (Vertical) LIMBUS - Dimensions
- 4. Provides limited nourishment to the peripheral cornea via the limbal vasculature. Site of the aqueous humor drainage system including Schlemm’s canal. This system is important for the maintenance of the intraocular pressure. LIMBUS - Functions
- 5. LIMBAL VASCULATURE Terminal arteries – Peripheral Cornea Arcades Recurrent arteries – Peripheral Conjunctiva Arcades
- 6. SCLERA Approximately spheroidal Collagenous Relatively avascular Relatively inactive metabolically Durable and tough
- 7. SCLERA - Composition 65% H2O (c.f. cornea 72-82%) Dry weight figures: 75% Collagen 10% other protein *Irregular arrangement of collagen results in an opaque tissue *In older eyes, fatty deposits may produce a yellowing of the sclera.
- 8. Sclera - Dimensions Approximately spheroid 22 mm diameter >80% of eye external surface Thickness - 0.8 mm at limbus - 0.6 mm at front of rectus muscle tendon - 0.3 mm behind rectus muscle insertions - 0.4-0.6 mm at equator of globe - 1.0 mm at optic nerve head
- 9. Lacrimal Gland Located under supero-temporal orbit Sits in Lacrimal Fossa Divided by Levator Palpebrae Superioris into: Orbital portion (larger, upper) Palpebral portion (smaller, lower)
- 10. Lacrimal Gland The lacrimal gland has up to 12 ducts two to five from the upper (orbital) portion six to eight from the lower (palpebral) portion. The ducts open onto the superior palpebral conjunctiva.
- 11. Accessory Lacrimal Glands GLANDS OF WOLFRING Similar in structure to the lacrimal gland. Situated near the upper border of the tarsal plate in the upper lid. Supplying the aqueous phase of basal tears.
- 12. Accessory Lacrimal Glands GLANDS OF ZEIS Sebaceous glands Associated with lash follicles Partially supply lipid layer of tears
- 13. Accessory Lacrimal Glands Meibomian Glands: Sebaceous glands Main supply of lipid layer of tears 25 in upper lid, 20 in lower lid (shorter) Oil on the lid margins prevents tear overflow
- 14. ACCESSORY LACRIMAL GLANDS GOBLET CELLS Unicellular sero-mucous glands In epithelium of conjunctiva Provides mucoid layer of tears
- 15. TEAR FILM
- 16. By eyelid action By movement of the globe Helps form lacrimal lake Each blink ‘resurfaces’ tear film Tear Distribution
- 17. TEAR FLOW Tear flow aided by: capillary action Gravity blinking
- 18. Distribution of Tear Volumes Pre-corneal: 1 μL Tear meniscus: 3 μL Cul-de-sac: 4 μL
- 19. Tear Film Stability Mucin layer spread by lid action enhances wettability of epithelium. Evaporation leaves an oil and mucin admixture. Admixture does not ‘wet’ epithelium causing a break-up of tear film
- 20. MECHANICS OF TEAR FILM SPREADING Upward lid movement draws aqueous component over the surface Lipid layer spreading over surface increases film thickness and stability
- 21. TEAR FLOW: LID CLOSURE MOVEMENT TOWARDS THE MEDIAL CANTHUS Lid closure is scissor-like towards the nose Tears move towards the medial canthus
- 22. The compressive force of blinking on the tears combined with the scissor-like action of lid closure, gives a directional flow towards the medial canthus.
- 23. Tear Drainage
- 24. EYELIDS
- 25. Modified folds of skin Protect eyes from foreign bodies and sudden increases in light level Spread tears over the ocular surface Lid margins are shelf-like and about 2mm wide EYELIDS
- 26. EYELIDS 4-LAYERED STRUCTURE 1.Cutaneous layer (the skin) 2.Muscular layer (mainly orbicularis oculi) 3.Fibrous tissue layer (tarsal plates) 4.Mucosal layer (palpebral conjuctiva)
- 27. EYELIDS-GLANDS ZEIS GLANDS •Sebaceous glands associated with lash follicle, They contribute to the lipid layer of the tears MOLL’S GLANDS •Modified sweat glands open into Zeis glands, lash follicles, lid margins MEIBOMIAN GLANDS •Sebaceous glands in the tarsal plate, main source of the tear lipid layer.
- 28. EYELIDS-GLANDS
- 29. EYELIDS: BLOOD VESSELS Supply oxygen to the cornea via palpebral conjuctival vessels.