Anatomy & physiology of human eye lens

this video is only meant for educational purpose .

1. Anatomy & Physiology of H uman Eye Lens BY . Hashim Saleem Khan (optometrist)

2. HUMAN EYE

3. ANATOMY OF LENS DEFINITION Lens – Transparent , Biconvex , crystalline structure Location – PATELLAR FOSSA – saucer shaped depression Position of Lens in Eye Ball : Lens lies between post surface of iris & the vitreous in a saucer shaped depression c/a patellar fossa. Post surface of lens is in contact with vitreous attached to it in a circular area with Wiegert’s ligament. There is a potential space between post lens capsule &Wiegert’s ligament c/a Berger’s space.

4. Dimension of Lens : Equatorial diameter of lens in adult is 9-10mm. During birth approximately 6.5 mm & attains max diameter in 2nd decade of life . -Axial diameter (Thickness) - A birth about 3.5mm - At extreme of Age 5mm Weight : 135 mg = 0 – 9 years. 255 mg = 40 – 50 years

5. Surfaces of Lens : Two Surfaces – ( i ) Anterior (ii) Posterior The ant. Surface is less convex & is a part of sphere having radius of 8 to 14mm. The post surface is more convex & is a part of sphere having radius of 4.5 to 7.5 mm. The two surfaces meet at the equator. Equator is almost circular and has an undulated appearance .

6. Poles of Lens : Ant . Pole lies in centre of ant surface and is about 3mm from the back of cornea. Post pole lies in centre of post surface . Refractive Index : R/I of Lens is 1.39 R/I of Cortex – 1.38 R/I of Nucleus – 1.42

7. Ref Power : About 16 – 17 D. Accommodative Power :- varies with age At Birth - 14 to 16 D At 25 years - 7 to 8 D At 50 years - 1 to 2 D Colour :- varies with age Colourless in infant & young adult Yellow tinge after 30 years Amber coloured in old age

8. Structure 1. Lens capsule : Thin, transparent hyaline Membrane. Thick at anterior than posterior 2. Anterior epithelium: Single layer of cuboidal cells become columnar Dividing & Elongating to form new lens fibres throughout Life. 3. Lens fibres: The epithelial cells elongate to Form lens fibres. 4. Suspensory ligaments ( Zonules of Zinn ): Also cilliary zonules consist series of lens fibres passing from cilliary body to lens , hold the lens in position & enable thee cilliary muscle to act on it.

9. Lens transparency Avascularity, Tightly-packed nature of lens cells, The arrangement of lens proteins, Semipermeable character of lens capsule, Pump mechanism of lens fibre membranes that regulate the electrolyte and water balance in the lens, maintaining relative dehydration and Auto-oxidation and high concentration of reduced glutathione in the lens maintains the lens proteins in a reduced state and ensures the integrity of the cell membrane pump .

10. Metabolism Lens requires a continuous supply of energy ( ATP) for active transport of ions and amino acids Source of nutrient supply : chemical exchanges with the aqueous humour Pathways of glucose metabolism 80 % glucose is metabolised anaerobically by the glycolytic pathway, 15 percent by pentose hexose monophosphate (HMP) shunt and a small proportion via oxidative Kreb's citric acid cycle. Sorbitol pathway is relatively

11. CATARACT: Development of an opacity in the lens is known as cataract . A. Etiological classification B . Morphological classification

12. A:Etiological classification (1)Congenital and developmental cataract (2) Acquired cataract 1 . Senile cataract 2 . Traumatic cataract 3 . Complicated cataract 4 . Metabolic cataract 5 . Electric cataract 6 . Radiational cataract 7 . Toxic cataract e.g., i Corticosteroid-induced cataract ii. Miotics-induced cataract iii. Copper (in chalcosis) and iron (in siderosis) induced cataract. 8 . Cataract associated with skin diseases (Dermatogenic cataract). 9 . Cataract associated with osseous diseases. 10 . Cataract with miscellaneous syndromes

13. B. Morphological classification 1. Capsular cataract. It involves the capsule and may be: i . Anterior capsular cataract ii . Posterior capsular cataract 2. Subcapsular cataract. It involves the superficial part of the cortex (just below the capsule) and includes: i . Anterior subcapsular cataract ii . Posterior subcapsular cataract 3. Cortical cataract. It involves the major part of the cortex. 4. Supranuclear cataract . It involves only the deeper parts of cortex (just outside the nucleus). 5. Nuclear cataract . It involves the nucleus of the crystalline lens.

14. THANK YOU