Ocular biochemistry
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Ocular Biochemistry Tears, Cornea, Lens, Aqueous, Vitreous, Retina and Rhodopsin. Tear Film Aqueous Humour Cornea Structure of Retina Visual Cycle
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Ocular biochemistry
- 1. Ocular Biochemistry Tears, Cornea, Lens, Aqueous, Vitreous, Retina and Rhodopsin For B.Sc Optometry Students
- 2. Tear Film Functions • Form a smooth optical surface by filling irregularities of corneal epithelium • Keeps the cornea and conjuctiva moist • Serves as a lubricant for lids • Transfer air to the cornea • Prevent infections • Washes away debris and irritants • Provides pathway to WBC in case of injury
- 4. 1 MUCIN LAYER • Deepest layer, 0.02-0.05 μm • Secreted by conjunctival goblet cells, crypts of Henle, gland of • Stabilizes tear film, Semisolid state, highly hydrated • Lubricates ocular and palpebral 2 AQUEOUS LAYER • The middle layer, Secreted by • Macromolecular muco3 LIPID LAYER Tear Film
- 5. 1 MUCIN LAYER • Deepest layer, 0.02-0.05 μm • Secreted by conjunctival goblet cells, crypts of Henle, gland of Manz and also by main Lacrinal gland • Made of glycoprotein, mixed with lipids, anchored by micro villi • Stabilizes tear film, Semisolid state, highly hydrated • Lubricates ocular and palpebral surfaces and reduces friction • Slippery coating over foreign bodies and protecting cornea and conjuctiva against abrasive effects Tear Film
- 6. 2 AQUEOUS LAYER • The middle layer, Secreted by lacrinal glands and accessory glands of Krause and Wolfring • 10 μm, It forms a uniform layer • Lysozyme, lactoferin, tear specific prealbumin and immunoglobulin A • Bicarbonate and proteins give bufffering capacity to tears • Macromolecular muco glycoproteins determine the surface tension of fluid • Provides atmospheric O2 to epithelium • Washes away debris and irritants Tear Film
- 7. 3 LIPID LAYER • Outer most oily layer, derived from Meibomian, Ziess and Moll glands • Contains lipids with low polarity such as wax and cholesterol esters • Fluid layer •Triglycerides, FFA, phospholipids are present in low amounts • Prevents overflow & reduce evaporation of tears Tear Film
- 8. Tear Film Chemical composition Water • Major component, 98.2% • With salts dissolved Na+, K+, Cl-, HCO3-, Ca2+ Proteins • Un-stimulated tears: 2gm/100ml • Stimulated tears: 0.3-0.7 gm/100ml • Group A: 15% of proteins, IgG, Albumin,Transferrin, Alpha-1 antitrypsin, Alpha1-antichymotripsin, beta-2-microglobulins. • Group B: synthesized by tear glands, also known as rapid migrating proteins. Lysozyme, IgA Albumin Tear specific protein (prealbumin) • Acidic protein, exact function is unknown, might be stabilizing thin tear film
- 9. Tear Film Chemical composition Immunoglobulins • IgA is most prominent • Produced by plasma cells in conjuctiva • defense against viral or bacterial antigens. • IgM and IgE are also found. Lysozyme • a proteolytic enzyme, net positive charge • Produced by acinar cells of lacrinal gland • work against bacterial infections • lysis of bacterial cell wall Glycolytic enzymes, lactate dehydrogenase Betalysin: antibacterial agent Mucopoly saccharides Glycoproteins Amino acids Lipids Metabolites: glucose, lactate, pyruvate, urea Electrolytes: Na+, K+, Ca2+
- 10. Aqueous Humour entire volume of fluid in the anterior chamber is replaced 12 times a day, i.e. once every 2 hours
- 11. Aqueous Humour Functions • Maintenance of intraocular pressure • They also have metabolic role 1. Cornea – takes glucose and oxygen, release lactic acid and carbon dioxide 2. lens – use oxygen, glucose, amino acids and potassium and release lactate, pyruvate and sodium • optical function : act as a diverging lens of low power • Clearing functions
- 12. Aqueous Humour Biochemical composition • Water 99.9% • Proteins - colloid content 1. 5- 16mg/100ml (plasma 6-7gm/100ml) because of blood aqueous barrier 2. IgM and IgG but NO IgD and IgA 3. Growth factors like FGF, TGF beta, IGF-1 4. Free amino acids • Non colloidal contents – dissolved solids 1. High vitamin C 2. High Pyruvate and lactate 3. Na, K, Ca, Mg, Cl, HCO3 4. low glucose and urea compared to plasma
- 13. Aqueous Humour Biochemical composition Anterior chamber • Lesser bicarbonate • Higher chloride • Lesser ascorbate • pH 7.6 Posterior Chamber • Higher bicarbonate • Lower chloride • Higher ascorbate • pH 7.57 The difference is due to diffusional exchange across the iris Iris vessels are permeable to anions and non electrolytes
- 14. Aqueous Humour: Biochemistry of formation
- 15. Aqueous Humour: Biochemistry of formation
- 16. Aqueous Humour: Biochemistry of formation
- 17. Aqueous Humour: Biochemistry of formation
- 18. Aqueous Humour: Biochemistry of formation Active transport • Sodium • Chloride • Potassium • Ascorbic acid • Amino acids • Bicarbonate Passive transport across NPE • Water • Chloride • Sodium
- 19. Cornea
- 20. • Water 70% • Enzymes necessary for metabolism • Acetylcholine • Electrolytes (Na+, K+, Cl-) Epithelium • Collagen fibrils 70% • soluble proteins (Ig G, A, M) • Proteoglycans: Keratin sulphate, • Enzymes • Matrix metalloproteinases (MMP-1, MMP-2, MMP-3) • Electrolytes Stroma Cornea
- 21. • Water 70% • Enzymes necessary for metabolism • Acetylcholine • Electrolytes (Na+, K+, Cl-) Epithelium Cornea
- 22. • Lens water – Dehydrated • Soluble Crystallins and insoluble albumiboids • Amino acids • Carbohydrates • Lipids • Electrolytes • Glutathione Lens
- 28. Structure of Retina Fovea centralis Optic Disc Structure of Retina
- 29. Vitamin A (Retinol) Diet Retinol Intestine Blood stream Liver Retinol binding protein + Retinol Retinal pigmented epithelium Photoreceptors
- 30. Change in Retinol Retinol Retinene Rhodopsin Retinine reductase (oxidation) Opsin Inside outer segment of photoreceptors
- 34. Visual Cycle
- 35. Visual Cycle : formation of nerve impulse 1. Rhodopsin changes to metarhodopsin in light 2. Metarhodopsin activates Transducin 3. Transducin activates enzyme phospodiesterase 4. Decreased intracellular cGMP 5. Closure of Na+ channel 6. Hyperpolarisation of rod cells 7. Decreased release of neurotransmitter 8. Response in bipolar cells 9. Signals to optic nerve and then to brain Steps
- 36. • Collagen is the main content of insoluble proteins in vitreous humor • Hyaluronic acid is glycosaminoglycan. It adds viscosity to the gel. It forms a water binding meshwork around collagen fibers • Soluble proteins has mainly glycoprotein and albumin • Sugar • Ascorbic acid • Amino acids • Electrolyte Vitreous Humor