physiology of cornea
Post on 16-Apr-2017
117 views
Embed Size (px)
TRANSCRIPT
CORNEAL PHYSIOLOGY -Riddhi Solanki B.OptomAditya Jyot Institute Of Optometry
*
Layers of cornea
8.bin
Primarily concerned with:The sources of energy which fuel the corneas metabolic activity.Corneal transparency & its maintenance.
Corneal PermeabilityWater Endothelium> EpitheliumOxygen Derived from atmosphereCarbon dioxide Permeability is 7times more than oxygen
Corneal permeability & other substancesSodium- endothelium > epithelium 100 timesGlucose & amino acids:metabolically activeAssociated molecules fluorescein
Low sodium permeabilityRelatively impermeable to water,lactic acid,amino acid, glucose,& large moleculesRelatively impermeable to associated and fat soluble entities
Role of cell junctionsCommunication Electrical couplingBarrier to - electrolytes
- fluid - macromolecules
General classification of junctionsOccluding or tightAdheringEach is further divided into shape & size of cell contact - zonulae(belts) - fasciae (bands) - maculae(focal)
9.bin
FibronectinCell surface glycoproteinInvolved in cell adhesion to surfacesReleased beneath generating epitheliumSynthesized by corneaFound in basal & apical surface of cultured endothelium cells.
Oxygen supply to corneaIt is the most important metaboliteDrives the supply from several surfaces
- atmosphere via tear film - capillaries of the limbal region - aqueous humor via corneal endothelium - capillaries of palpebral conjunctiva
Carbon dioxide effluxOpen eye
from cornea & aqueous humor into tear film Closed eye
into the aqueous humor
10.bin
Metabolism corneal energy by carbohydrate metabolismGlucose enters cornea from aqueous humorEnergy:ATP
anaerobic:breakdown of glucose into lactic acid aerobic: breakdown of glucose by TCA cycle into carbon dioxide & water
Sources of glucose to corneal epitheliumAqueous humor (90%)Limbal blood vessels & tears(less than 10%)
11.bin
Glucose consumption30-90mg /hr40-60% of total consumption is by the epithelium
Glucose metabolic pathwayEMBEDEN-MAYERHAOFF PATHWAY produces lactate (anaerobic)+2ATPTRICARBOXYLIC ACID CYCLE aerobic HEXOSE MONOPHOSPHATE SHUNT aerobic produces NADPH,CO2,H2O& 6ATP
Lactic acidNot metabolized by corneaRemoved by diffusion into aqueous humorAccumulation results in epithelial & stromal oedemaHypoxia doubles lactic acid concentration resulting in an osmotic gradient
CORNEAL TRANSPARENCYFactors Affecting Corneal Transparency:
Corneal Epithelium and Tear Film Arrangement of Stromal LamellaeCorneal VascularisationCorneal Hydration
*
Corneal transparency: stromaTransmits 90% of incident lightPotentially a non-transparent layerFibrils: n=1.47Ground substance: n=1.37Regular fibril spacing :60 m
Diffraction theory of MauriceDepends on ordered arrangement of collagen fibrilsTransparency is maintained if the disruption is less than few wavelengthScattering effect increases as swelling increases(fibrils become larger optically)
Corneal swellingLactate & metabolite accumulation- osmotic gradient causes water imbibitionHydrophilicity of GAGs causes a natural water imbibitionSwelling sleep is due to : hypoxia (50%) lower water osmolarity increased temperature & humidity
It effects:Change in refractive index of intra & extracellular spacesSattlers vielhaloes
Histochemical examination has shown presence of the endothelium of enzymes needed for glycolysis & krebs cycle
The endothelial pump
Drug Permiability Across CorneaLipid And Water Solubility Of The DrugMolecular SizeWeight And Concentration Of The DrugsIonic Form Of The Drugs
**