2020–2021 BCSC Basic and Clinical Science Course™
2 Fundamentals and Principles of Ophthalmology
Part IV: Biochemistry and Metabolism
Chapter 10: Lens
Transparency and Physiologic Aspects of the Lens
Transparency of the lens depends on the precise organization and maintenance of its elements. This is accomplished structurally by the orderly spatial distribution of the lens fibers and by the tight connections formed between them via specialized interdigitations (Fig 10-2). Light scatter is reduced by the minimized space between cells. Scatter is also diminished by the loss of nuclei and organelles as the lens fibers elongate and approach the visual axis. Light scatter alters lens transparency, thereby affecting vision. Loss of transparency can have beneficial effects. In the aging lens, accumulation of yellow chromophores protects the retina from shorter wavelengths of light.
The cornea and aqueous humor protect the retina from wavelengths below the visible spectrum. The visible spectrum refers to the part of the electromagnetic spectrum that is perceived as light, with wavelengths normally considered to range from 400 nm to 700 nm. Wavelengths shorter than 400 nm are referred to as UV light. Wavelengths of 300 nm or below are blocked by the cornea and by ascorbate (vitamin C), which is present at high levels in the aqueous humor. Wavelengths of 360 nm or below are blocked by the lens (Fig 10-3).
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.