Most old fibres of the lens are located in the -
Ans. is 'b' i.e., Centre o There are three structural elements that make up lens -1) Lens capsule# A transparent membrane surrounding the lens like a pocket. It is thicker over the anterior surface than the posterior surface. It is thickest at pre- equator region and thinnest at the posterior pole. When an artificial lens replaces the natural lens in cataract surgery (IOL implantation), it is placed in this same capsule.2) Lens epithelium# It is a single layer on the anterior (front) surface of the lens. There is no epithelium on posterior surface. The epithelial cells distribute fluid, ion and glucose through the entire lens. They also create new fibers throughout a person's life.3) Lens fibres# These are long protein fibers that are closely packed and parallel. They make up most of the lens volume and are laid horizontally, front to back, and concentrically like layers of an onion. As the lens fibres are formed through out the life, these are arranged compactly as nucleus and cortex of the lens.a) Nucleus: - It is the central part containing the oldest fibres, it consists of different zonesi) Embryonic nucleus:- Formed at 1-3 months of gestation, therefore consists the oldest primary fibres.ii) Fetal nucleus: - Lies around the embryonic nucleus and is formed from 3 months of gestation till birth.iii) Infantile nucleus:- Corresponding the lens from birth to puberty and surrounds the fetal nucleus.iv) Adults:- Corresponds to the lens fibres formed after puberty to rest of the life.b) Cortex:- It is the peripheral part containg the youngest fibres.
Periphery
Centre
Superior portion
Inferior portion
Miscellaneous (Lens)