Biology: The Lens and Accommodation

Higher protein concentration

To allow the eye to focus at different distances

Cartilaginous fish

To nourish the retina and control vitreous body pH

Biconvex, 10 mm

Spherical

By moving the lens or retina laterally

Lower protein content, more aqueous

Fibrillin, a type of connective tissue with elastic properties

The lens becomes more globular

A layer of collagen fibrils embedded in a glycosaminoglycan matrix

Because the cornea is less dense than water

Hexagonal

The presence or absence of a nucleus

To facilitate metabolic communication

To regulate refractive index

By continually adding new fibres to the central portion

6.5 mm

The process involves the elongation and differentiation of epithelial cells at the equator, where they form columnar cells that become arranged in rows.

The apical surface of the cell grows and pushes anteriorly, while the basal surface grows and pushes posteriorly, eventually meeting opposite fibers at irregular sutures.

Lens bow

Adult lens fibres are secondary lens fibres, whereas embryonic lens fibres are primary lens fibres.

The equatorial region is where epithelial cells elongate and differentiate into lens fibres.

Lens fibres push under the capsule, with the anterior surface pushing anteriorly and the posterior surface pushing posteriorly.

The lens fibres do not meet at the poles, but instead, form irregular lines called sutures. This arrangement allows for a smooth, continuous curvature of the lens, which is essential for its refractive function.

Cortical fibres have a nucleus and organelles, whereas nuclear fibres lack these structures. This difference affects the metabolism and function of the fibres, with cortical fibres being more active and nuclear fibres being more compact and dense.

Lens fibres communicate with each other through a high concentration of gap junctions, which enable metabolic communication and coordination between the fibres. This communication is essential for the maintenance of the lens's integrity and function.

The lens grows throughout life by continually adding new lens fibres to the central portion of the lens, without discarding any of its cells. This growth allows the lens to maintain its function and adapt to changes in the environment.

The lens nucleus has a higher protein concentration than the cortex, with a gradient of 200-300 mg/ml in the nucleus and 100-150 mg/ml in the cortex. This difference in protein concentration creates a refractive index gradient, which is essential for the lens's ability to focus light.

The transparent and biconvex structure of the lens allows it to focus light at different distances, enabling accommodation.

The tight packing and interlocking of lens fibres allows for a compact and rigid structure, which enables the lens to maintain its shape and refractive function. This arrangement also facilitates the transmission of light through the lens.

The lens grows throughout life, with the axis length increasing at a rate of 0.023mm/year.

The zonules of Zinn are fibers that hold the lens in place, and they are composed of fibrillin, a connective tissue with elastic properties.

The equator of the lens is encircled by the ciliary processes of the ciliary body, and lies 0.5 mm from them.

When the ciliary muscles contract, the lens assumes a more globular shape, and the pupil becomes smaller.

The lens is able to change its dioptric power because it can change its shape, allowing it to focus on objects at different distances.

The hexagonal cross-section of lens fibres allows for tight packing and interlocking, which facilitates the lens's function by minimizing space between fibres and reducing light scattering.

Cortical fibres have a nucleus and organelles, whereas nuclear fibres lack them; this difference is significant because it affects protein concentration and refractive index.

Gap junctions enable direct cell-to-cell communication, allowing for metabolic cooperation and coordination between lens fibres.

Lens fibres grow throughout life, with new fibres continually added to the central portion of the lens; this growth is significant because it allows the lens to maintain its function and adapt to changes in the eye.

The alignment of lens fibre nuclei in the cortex enables the lens to maintain its shape and function, allowing it to focus light efficiently.

The nucleus has a higher protein concentration than the cortex, which affects the refractive index and the lens's ability to focus light.

The epithelial cells elongate and form columnar cells, which become arranged in rows. The lens cells elongate and turn, so that their long axis is parallel to the surface of the lens.

The alignment of newly produced lens fibre nuclei in the lens cortex is significant for the structure and function of the lens. This arrangement is known as the lens bow.

Lens fibres grow and push under the epithelium and capsule through a process of cell elongation and multiplication. This process is significant for the growth and development of the lens throughout life.

Gap junctions in lens fibres facilitate communication between fibres, allowing for the exchange of ions and small molecules. This communication is significant for maintaining the homeostasis and osmolarity of the lens.

Adult lens fibres are elongated cells that form the main mass of the lens. They differ from embryonic lens fibres in terms of their structure and function, with adult fibres being more organized and specialized.

The equatorial region is significant for lens fibre formation, as it is the site where epithelial cells elongate and form columnar cells. This region contributes to the growth of the lens by producing new fibres that push under the epithelium and capsule.

The distinct arrangement of lens fibres at the poles allows for efficient transmission of light and facilitates the lens's function in focusing light.

Lens epithelial cells transform into lens fibres through a process of fibre formation, which involves cell elongation, nucleus migration, and fibre differentiation; this process is crucial for the growth and development of the lens.

Lens fibres grow throughout life through the process of fibre formation and differentiation, which allows the lens to accommodate for near and far vision; this growth is significant for maintaining proper vision.

The high concentration of gap junctions in lens fibres allows for direct cell-to-cell communication and coordination of fibre function, facilitating proper lens function.

The alignment of newly produced lens fibre nuclei in the lens cortex allows for proper fibre organization and facilitates the lens's function in focusing light.

Lens fibre growth is influenced by the capsule, which provides a framework for fibre organization and differentiation; this relationship is crucial for proper lens development.