this video is only meant for educational purpose .

1. Anatomy & Physiology
of Human Eye Lens
BY. HASHIM SALEEM KHAN
(OPTOMETRIST)

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.