The cornea consists of three layers - epithelium, stroma, and endothelium. Its primary functions are to maintain transparency and protect the intraocular contents. Transparency is determined by the peculiar arrangement of corneal lamellae, its avascularity, relative dehydration, metabolism, and higher refractive index difference with air. The stroma is composed of collagen fibers set in mucopolysaccharides that form a regular hexagonal lattice, leading to destructive interference of scattered light rays below 200nm that maintains transparency. Corneal avascularity and dehydration are maintained by genes, nutrients from the atmosphere, perilimbal capillaries, and aqueous humor pumps in the epithelium and endothelium.

1. CORNEAL
TRANSPARENCY
JAYADEVI.A

2.  Primary physiological functions of the cornea is
to maintain its transparency and protect the
intraocular contents
 Cornea consists of three layers
epithelium
stroma
endothelium

3. 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

4. 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

5. 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

6. 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.

7.  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

8. •

9.  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

10.  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

11.  Recent studies suggested that corneal
keratocytes contain two water soluble
proteins
transketolase
aldehyde dehydrogenase
class 1A1