Cornea1a.ppt

Functions: Lens – therefore curved Window – therefore transparent Protection – therefore strong Properties: Isolated from blood supply Avascular Temperature 38ºC  1 ºC Diameter : 10.6mm (vertical) 11.7mm (horizontal) Thickness : 0.52mm (central) 0.67mm (peripheral) Radius of Curvature : 7.7mm-8.1mm...

Functions: Lens – therefore curved Window – therefore transparent Protection – therefore strong Properties: Isolated from blood supply Avascular Temperature 38ºC  1 ºC Diameter : 10.6mm (vertical) 11.7mm (horizontal) Thickness : 0.52mm (central) 0.67mm (peripheral) Radius of Curvature : 7.7mm-8.1mm (anterior) 5.81mm-6.65mm (posterior) Refraction : about 65% of total power of eye (~ 48D anterior; ~ -6.3D posterior) Refractive index : 1.376 Anatomy of the Cornea Five layers: Epithelium Bowman’s layer Stroma Descemet’s membrane Endothelium Mostly stroma! Epithelium Most anterior layer 5-6 cells thick 50m thick Most regular squamous stratified epithelium in body With tear film provides optically smooth front surface to cornea Squamous- a stratified epithelium that consists at least in its outer layers of small 3 TYPES a) Squamous b) Wing c) Basal Under go 10 day cycle 1 Basal 2 Wing 3 Squamous Programmed cell death – apoptosis Different to cell death from infection or injury Cells bound together Desmosomes Epithelium is a passive barrier Stops water entering the stroma below Basal cells have gap junctions Continual loss of cells from surface. Only basal cells capable of division. Repair by means of basal cells and limbal stem cells BOWMAN’S LAYER Modified portion of stroma No cells; Narrow collagen fibrils; 12m thick Some species – no Bowman’s layer! Corneal Stroma Provides: strength elasticity form of cornea Comprised of collagen Triple alpha Helix? Alpha helical coiled coil collagen fibril structure Collagen fibrils withstand radial tension Proteoglycans withstand compression along AB B A Lamellae are arranged parallel to corneal surface Corneal lamellae Contain parallel collagen fibrils Run at various angles from limbus to limbus Typically 1.5-2.5m thick Human stroma contains about 200 lamellae in its thickness Posterior lamellae don’t interweave Anterior lamellae do interweave Human Superior stroma More collagen this way than this Important for mechanical strength Inferior way Keratoconus (conical cornea) = keratocyte Keratocytes Mostly between lamellae Flattened cells with long pseudopodia in contact with each other Occupy about 10% of stromal volume Responsible for slow turnover Prooduce collagen fibres and help maintain fibril order Important in wound healing Composition of the bovine corneal stroma (from Maurice, 1984) Substance % Water 78 Collagen 15 Other proteins 5 Proteoglycans 1 Salts 1 Proteoglycans: long repeating sulphated disaccharides highly negatively charged – attract water attached to protein core act as collagen spacers 6-12m thick Descemets Membrane Structureless band – gives mechanical strength and a base for endothelium 6m thick Endothelium Most posterior layer One cell thick 4-8m thick Source of endothelial pump 3500 cells/mm2 in 10 to 19 year-olds Hexagonal cells 2300 cells/mm2 in 80 to 89 year-olds Cells do not usually divide, so cover a larger area by spreading during growth or following injury PUB QUIZ TIME! Who won the FA cup in 1956 ? What was the score ? Manchester City The beat Birmingham city 3-1 (1) (1) 1 Name the two lobes of the lacrimal gland What seperates them ? 2 Where are the goblet cells ? What do they produce ? 3 Where are the meibomian glands ? What do they produce ? 4 To widen palpebral fissure the upper tarsal plate is pulled up by which two muscles ? 5 Name the different types of cell in the epithelium of the cornea How long to they take to complete a cycle? 6 The lacrimal gland is under the influence of which part of the brain? What are the three classifications of nerves which innervate the lacrimal gland? 7 What is the structural form of a collagen molecule ? What is the contribution (in %) of the cornea to the total refractive power ? 8 What is the plica semilunaris ? What is ptosis ? Which is the main muscle involved in ptosis ? 9 Classically, what are the three layers of the tear film? What percentage of tears are produced by the accessory glands? 10 What mechanism is thought to drive the drainage system of tears ? Dr Regini belongs to which rowing club ? 1 Name the two lobes of the lacrimal gland What seperates them ? Orbital and Palpebral (2) Levator aponeurosis tendon (2) 2 Where are the goblet cells ? What do they produce ? Conjunctiva Mucus (1) (1) 3 Where are the meibomian glands ? What do they produce ? Inside the tarsal Plates (1) Oil/lipids (1) 4 To widen palpebral fissure the upper tarsal plate is pulled up by which two muscles ? levator aponeurosis (2) superior tarsal muscle (Müller’s) (4) 5 Name the different types of cell in the epithelium of the cornea How long to they take to complete a cycle? Basal, Wing & Squamous (3) 10 Days (1) 6 The lacrimal gland is under the influence of which part of the brain? What are the three classifications of nerves which innervate the lacrimal gland? hypothalamus (1) Sensory, parasympathetic & sympathetic (3) 7 What is the structural form of a collagen molecule ? What is the contribution (in %) of the cornea to the total refractive power ? Trippel alpha helix (2) 65% (1) 8 What is the plica semilunaris ? What is ptosis ? Which is the main muscle involved in ptosis ? vestigial “third eyelid” (1) Droopy upper eye lids (1) levator aponeurosis (2) 9 Classically, what are the three layers of the tear film? What percentage of tears are produced by the accessory glands? lipid, aqueous & mucous layers (3) 10% (1) 10 What mechanism is thought to drive the drainage system of tears ? Dr Regini belongs to which rowing club ? Pressure gradients (2) Llandaff RC (10) Limbus The Limbus nourishment of peripheral cornea Corneal wound healing Immunosurveillance Contains pathways of aqueous humour outflow Contains circumferential or tangential collagen fibrils Site of surgical incisions The sclera Outer coat of eye Contains collagen, proteoglycans and elastic fibres Relatively avascular Thickness: 1mm (posterior) 0.4mm behind muscle tendon insertions Variable fibril diameter Corneal stroma Scleral stroma Corneal nerves Derived from ophthalmic division of trigeminal nerve Branches radiate to anterior cornea from limbus Nerves loose myelin sheaths in cornea Terminal axons very sensitive to pain and temperature Endothelium in human not innervated Corneal touch threshold (CTT) Soft (low CTT) Medium Stiff (high CTT) Sensitivity (s) = 1/CTT S S Nasal Temporal Inferior Superior