corneal transparency
TRANSCRIPT
CORNEAL TRANSPARENCY
JAYADEVI.A
Primary physiological functions of the cornea is to maintain its transparency and protect the intraocular contents
Cornea consists of three layers epithelium stroma endothelium
FACTORS DETERMINING TRANSPARENCY Peculiar arrangement of corneal lamellae
Avascularity
Relative state of dehydration
Metabolism of cornea
Higher difference between refractive index of cornea and air
STROMA
Transparency of cornea is related to the regularity of stromal components
Stroma is composed of type1 collagen fibers set in ground substance of mucopolysaccharides
This ribbon like bundle formation gives the laminated appearance
Collagen fibers are spaced equidistantly and form the hexogonal lattice
LATTICE THEORY Lattice formation leads to interfibrillar
spacing of less than the wave length of light.
so that tangential rows of fibers acts as a diffraction grating resulting in destructive interference of scattered rays
GOLDMAN AND BENEDEK THEORY It is based on dimension of refractive
elements in corneal stroma. There is least scattering of light till
spatial dimension of variations in refractive index remains <200 nm.
Corneal avascularity is maintained by PAX6 GENE & DESTRIN
The main source of nutrition is atmospheric air-oxygen perilimbal capillaries aqueous humor The relative state of corneal dehydration is
mainly due to epithelial and endothelial pumps
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Atmospheric oxygen dissolved in pre corneal tear film
perilimbal capillaries & aqueous provides solutes
Deeper parts of cornea obtains nutrition from aqueous
Endothelium needs oxygen and glucose for metabolic activity & proper functioning of pump
Cornea derive their energy requirements from phosphorylation of carbohydrates and auto oxidative system
Glucose enters cornea either by simple diffusion or active transport
Breakdown of glucose in cornea occurs by aerobic & anaerobic process into carbondioxide & lactic acid
Recent studies suggested that corneal keratocytes contain two water soluble proteins
transketolase aldehyde dehydrogenase class 1A1
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