Crystalline lens - by Ashith Tripathi

This ppt covers anatomy, dimensions, microscopic structure, arrangement of lens fibers, ciliary muscles, Nucleus development, accommodation and its theories etc...
It is useful for optometry students, educational purposes etc..
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1. U.P.U.M.S. Paramedical Vigyan Mahavidhyalaya

2. Represented by - Ashith Tripathi Submitted to – Gaurav sir Crystalline lens

3. introduction The lens of the eye is a transparent, biconvex, elliptical, semi solid, avascular body of crystalline appearance located between the iris and the vitreous . Weight of lens varies with age .

4. Equatorial diameter 6.5 mm at birth, increases to 9 to 10 mm in the second decade and then remain almost constant.

5. Thickness (axial or anterioposterior diameter ) varies with age between 3.5 mm (at birth ), about 4 mm at 40 years and increase slowly to 4.75 to 5 mm in extreme old age . The weight is approximately 260 mg at 70 - 80 years of age . In males, the lens weight more than the aged matched females, with a mean difference of 7.9 to 2.47 mg.

6. surfaces Lens has two surface- Anterior surface Posterior surface

7. It is less convex than the posterior surface. The anterior surface is the segment of a sphere whose radius average 10 mm. The center of anterior surface is known as the anterior pole, and is about 3 mm from the back of the cornea. Anterior Surface

8. It is more curved than the anterior and present a radius of about 6 mm (4.5-7.5) . The centre of posterior surface is called as posterior pole. It lies in a fossa lined by the hyaloid membrane on the front of the vitreous. Posterior surface

9. Refractive index The refractive index of the lens is 1.39 ( nucleus 1.42, cortex 1.38 ) , which is slightly more than that of the aqueous ( 1.336 ) and vitreous humor ( 1.3349 ). The refractive power is about 16 – 17 dioptres, out of a total of about 60 diopters for the normal eye.

10. Accommodative power is 15 - 16 diopters, diminishing to half of this at about 25 years of age and to 2 diopters or less at age 50 years.

11. Structure The lens consists of – The lens capsule The lens epithelium and The lens cells or fibers Structure

12. Lens capsule It is a thin, transparent, hyaline collagenous membrane which surrounds the lens completely . The lens capsule is highly elastic but does not contain any elastic tissue.

13. Characteristics of the lens capsule The capsule completely envelops the lens and the cells of origin are completely contained in it . The capsule is the basement membrane of the lens epithelium and is the thickest basement membrane of the body .

14. It is much thicker in front than behind and the anterior and posterior portions are thicker towards the periphery ( equator ) just within the attachment of the suspensory ligament than at the poles.

15. The thickness at the posterior pole is 2.8 – 4 microne meter and at anterior pole is 15.5 microne meter. Capsule thickness increase anteriorly with age. Under the light microscope the capsule appears transparent, homogenous. On microscopes

16. However, on ultramicropic examination, it shows a lamellar appearance . Under electron microscope the capsule appears to have a relatively amorphous appearance . There are up to 40 lamellae each of which is 40 mm thick.

17. The lens epithelium The lens epithelium consists of a single shut of cuboidal cells spread over the front of the lens, deep to the capsule and extending outwards to the equator. There are about 500,000 cells in the mature lens. There cells contain all the organelles found in a typical epithelium cell .

18. Almost all the metabolic, synthetic and transport process of the lens occur in this layer. equator

19. Zones of lens epithelium There are 3 zones in the lens epithelium. The central zone represents a stable population of cells. The intermediate zone is peripheral to central zone and its cells are smaller. The germinative zone is the most peripheral and is located just pre equatorially.

20. Features of lens epithelium The highest metabolic rate occurs in the anterior lens epithelium, because the content of ATP and enzymes is highest in this area of lens.

21. The lens fibres The epithelial cells elongate to form the lens fibres are formed from the posterior epithelium which runs from posterior to anterior to fill the lens vesicle. But later on, the lens fibres are derived from the cells of the equatorial region of the anterior epithelium. These cells divide, elongate and differentiate to produce long, thin, regularly arranged the bulk of the lens .

22. Mature lens fibres have no organelles or nuclei.

23. Zonal arrangement of lens fibres The lens fibres are formed throughout life and are arranged in zones that describe the various development periods of the lens. Nucleus Cortex Nucleus – I t is central part containing the oldest fibres. It consists of different zones. Embryonic nucleus is its innermost part. (formed at 1 to 3 months of gestation )

24. Fetal nucleus (corresponding to lens from 3 months of gestation till birth ) Infantile nucleus ( corresponding to lens from birth to puberty ) Adult nucleus (corresponding to the lens in adult life) b) Cortex – it is peripheral part of the lens substance which lies just outside the adult nucleus. It include the youngest lens fibres.

25. The ciliary zonules The ciliary zonules ( zonules of Zinn or suspensory ligament of lens ) consists essentially of a series of fibres which run from the ciliary body and fuse into the outer layer of the lens capsule around the equatorial zone . Thus, they hold the lens in position and enable the ciliary muscle to act on it.

26. accommodation Accommodation is the ability to increase the refractive power of eye by changing the shape of the crystalline lens. Accommodation is the process by which one can focus the object at differences in a bid to have a clear vision. In humans the process of accommodation is achieved by a change in the shape of the lens.

27. ashith tripathi Directed by - Guided by - Mr. Gaurav dubey

28. Special thanks Gaurav sir Thanks Aman Tiwari Himanshu Yadav Shiv pratap Dadhesh mathur Rajat bansal

29. Design and animated by - Ashith tripathi Aman Tiwari Videos from – U tube