corneal transparency

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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