cornea Anatomy , physiology, corneal breaks and emergencies By MAIS IBRAHIM M.D SYPERVISED BY RASHA GAZALI M.D Anatomy • Vertical diameter : 12 mm • Horizontal diameter : 11 mm • Radius of curvature : ant, 7.8mm – post, 6.5mm • Thickness : 1mm peripherally – 0.5 mm centrally Anatomy • Five layers : • 1- Epithelium • 2-Bowman • 3- Stroma • 4-Descemet Membrane • 5-Endothelium anatomy Epithelium • 50 micro m (5-10% ) • 1- basement membrane • 2- columnar basal cells (single layer) • 3-wing cells (2 to 3 layers ) • 4- surface cells • Stem cells at the limb Epithelium • Superficial cells : microvilli and microplicae coated with “glycocalyx” • Glycoprotein : stability of tear film and wetting of cornea • Sugar residues of plasma membrane glycoprotein and glycolipids : wound healing ,attachment of microbes Epithelium • Penetrating the epithelium : uncharged molecules • Penetrating stroma : charged • It should be able to dissociate at physiologic PH and temperature (biphasic) Bowman layer • Collagen fibers type I and type V • 8-10 micro m • Acellular and packed distribution ; prevent keratocytes from growth factor • PRK and LASEK ; corneal haze • Can not regenerate • Scar tissue after injury PRK LASIK flap Stroma • 90% of the cornea • 1- keratocytes (2.4 millions) • 2- ground substances ( proteoglycans) • 3- collagen lamellae Stroma • Collagen fibers ; center to center • Collagen type I ; 70% of stroma • Type III ; wound healing • Type V , VI , VII , XII , XIV PROTEOGLYCANS • 10% • Hydrophilic properties • 1-keratan sulfate 60% • 2-chondroitin sulfate • 3-dermatan sulfate 40% • Regulation of spacing between collagen fibrils MMPs • Degradation of the components of the extracellular matrix • MMT-2 ; normal cornea • MMT-1 , MMT-3 , MMT-9 after injuiry Descemet membrane • True membrane • 10-12 micro M • Increases with age • Secreted by endothelium • Type IV is the most one • Ending peripherally at shwalbe line Descemet membrane • Anterior banded zone – posterior nonbanded zone • Resistance to the flow of solvent Descemet defects • 1- descemet folds • 2-haab’s striae • 3-vogt striae • 4- hydrops Descemet folds • Inflammation: infection • Inflammation after surgery : normal or complicated surgery, retained lens fragments, RD, endo • Inflammatory conditions: belpharitis, phlyctenulosis, episcleritis, scleritis • Trauma , injury Descemet folds Haab’s striae • In primary congenital glaucoma • Breaks in descemet membrane • Stretching of the cornea • Horizontal in CG • Vertical or oblique : descemet’s tears in birth trauma Haab’s striae Vogt striae • Vertical • Keratoconus • Disappear with compression Vogt striae Vogt striae Corneal hydrops • Acute onset of corneal edema • Break in descemet membrane • Advanced keratoconus • Air or gas into AC may help recovery • Scars, corneal flattening may occur Hydrops Endothelium • Mono layer of polygonal/hexagonal cells • 3000/mm • Decreases with age 0.6% per year • 500/mm === EDEMA Endothelium function • 1- permeability barrier • 2- pump to maintain dehydration state • 3-negative hydrostatic pressure After injuries • Endothelium cells become fibroblastic • Synthesize retrocorneal fibrous membrane (RCFM ) • Decrease in VA • Express type I RCFM Dua’s layer • 15 micro m • Strong and impervious to air • Type II air bubbles • Optical and electron microscopy • May improve outcomes for patients will have grafts and transplants CORNEAL INNERVATION • Long posterior cilliary nerves (branches of V1 the ophthalmic division of cranial nerve V) • Cold and pain CORNEAL NERVES Corneal nerves CORNEAL NUTRITION • Oxygen : tear film, eyelid vasculature, AH • Glucose : Stroma; AH , carrier mediated transport through the endothelium Epithelium; tear film and limbal blood vessels Endothelium ; AH Corneal nutrition • Glucose metabolized : • 1-tricarboxylic acid (TCA) cycle • 2-anaerobic glycolysis • 3-hexose monophosphate (HMP) shunt • Epithelium and endothelium : HMP (35-65)% • Keratocytes : little glucose via this way cuz they lack 6-phosphogluconate dehydrogenase • Endothelium : TCA more than epithelium • Pyruvic acid : TCA ; aerobic • Lactic acid : anaerobic .. Accumulation ; edema; affect VA (contact lenses) Emergences • Chemical burns • Trauma • Foreign body • Corneal erosions Chemical burns • Alkali, acid, alcohol . • Alkali worse ; increased penetrating • First aid: irrigation Chemical burns - signs • Epithelial defect • Cloudy cornea • Conj. Hyperaemia • Caution : if cornea limbus is blanched Chemical burns Chemical burns Chemical burns-after recuvery Chemical burns-management • Irrigation • Topical antibiotics, steroids, citrate and ascorbate ( buffer alkali and inhibit proteinase enzymes, support new collagen from keratocytes) • vitamins A Trauma • Laceration, perforation • Full thickness , urgent surgery • SEIDEL TEST • No drops • History, ct Corneal foreign body Foreign body removing FB after recovery Corneal abrasion/erosions/welding flash burn • Large or small • Chloramphenicol • Contact lenses ? Flashing weld burns Erosions THANKS FOR LISTENING .