corneal physiology

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  1. 1. By Sinchana S Kumbar
  2. 2. Cornea It is considered the main refractive surface of the eye. Its power about +43 diopters. Protection of the intraocular structures of the eyes. Passage of images of objects to the retina.
  3. 3. Corneal Function 1. Forms the anterior 1/6 of the outer tunic . 1. Completely transparent. 2. Avascular. 3. It has smooth anterior and posterior surfaces . 4. Acts as a refractive medium.
  4. 4. Corneal epithelium 1. To form a smooth refractive surface . 2. Protects the cornea and intra ocular structures from infection by pathogens. 3. It contains 5-6 layers of cells mitosis occurs in basal cell layer , and moves upward by differentiating themselves into wing cells, flattend cells and finally superficial cells .
  5. 5. 4. Epithelium maintainance >processs of cell migration - migration of new basal cells into cornea from limbus. - migrate centripetally at about 120mm/week - originate from stem cells in limbal Epithelium. 5.Any injury to this layer renders extereme pain due to i. Exposure and ii. Stretching of nerve endings.
  6. 6. Bowmans membrane 1. Next to corneal epithelium . 2. Composed of - Fibrous sheet of interwoven collagen fibrils randomly arranged in a mucoprotein ground substance. 3. It cannot regenerate once destroyed scar. 4. Highly resistant to injury / infection . 5. Does the barrier function to micro organisms .
  7. 7. Corneal Stroma 1.It constitutes about 90% of total corneal thickness. 2.It appears homogenous. 3.It is comprised of i. collagen fibrils ii. Keratocytes iii. Ground substance
  8. 8. Theories that explain the arrangement of collagen fibres in stroma i. Maurice theory (1957) It states that collagen fibers are arranged in regular lattice , separated by less than a wavelength of light so that unscattered light is destroyed by mutual interference . ii. Goldmann theory States that cornea is transparent because fibrils are small in relation to light and dont interfere with the light transmission .
  9. 9. Lamellae- 1. Arranged through out stroma uniformly . 2. Cornea has a higher risks of crosslinking on damage and is more rigid, helping to maintain corneal curvature. 3. Its arrangement also helps in corneal transparency. Keratocytes 1. Flattened cells , present between lamellae 2. When stroma is injured , inflamed - they produces collagen fibers . 3. It plays a major role in maintaining transparency and wound healing . Ground substance Extra cellular matrix made up of ground substances such as - GAG : Keratin Sulphate and Chondroitin Sulphate .
  10. 10. Descemets membrane 1. It is strong , homogenous membrane . 2. Composed of collagen fibrils and glycoprotein . 3. It is highly resistant to trauma , proteolytic enzyme . 4. Even when whole of the stroma is slaughed off descemets can maintain the integrity of the eye ball . 5. It can be regenerated if the cells are lost . 6. Tense membrane
  11. 11. Endothelium 1. Innermost layer of cornea . 2. Polyhedral shaped cells endothelial mosaic model. 3. These cells do not divide or replicate . 4.Cell density goes on decreasing normally with age. 5.Disruptions to the endothelial mosaic can include endothelial cell loss or an increase in the variability of i. Cell shape (pleomorphism) ii. Cell size (polymegathism)
  12. 12. Specular Microscopy
  13. 13. Corneal Hydration . Corneal transparency Corneal metabolism are the important processes that occur in cornea
  14. 14. Remington AL .Clinical Anatomy and Physiology of the Visual System.3rd ed .Elsevier:Duncan L ;2012. REFERENCE