Accommodation is the process by which the vertebrate eye changes optical power to maintain a clear image or focus on an object as its distance varies. In this, distances vary for individuals from the far point—the maximum distance from the eye for which a clear image of an object can be seen, to the near point—the minimum distance for a clear image.
Accommodation usually acts like a reflex, including part of the accommodation-vergence reflex, but it can also be consciously controlled. The main ways animals may change focus are:
Changing the shape of the lens.
Changing the position of the lens relative to the retina.
Changing the axial length of the eyeball.
Changing the shape of the cornea.
Focusing the light scattered by objects in a three dimensional environment into a two dimensional collection of individual bright points of light requires the light to be bent. To get a good image of these points of light on a defined area requires a precise systematic bending of light called refraction. The formed from millions of these points of light is what animals see using their retinas. Very even systematic curvature of parts of the cornea and lens produces this systematic bending of light onto the retina. Due to the nature of optics the focused image on the retina is always inverted relative to the object.
Different animals live in different environments having different refractive indexes involving water, air and often both. The eyes are therefor required to bend light different amounts leading to different mechanisms of focus being used in different environments. The air/cornea interface involves a larger difference in refractive index than hydrated structures within the eye. As a result, animals living in air have most of the bending of light achieved at the air/cornea interface with the lens being involved in finer focus of the image. Generally mammals, birds and reptiles living in air vary their eyes' optical power by subtly and precisely changing the shape of the elastic lens using the ciliary body.
This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.
The ciliary muscle is an intrinsic muscle of the eye formed as a ring of smooth muscle in the eye's middle layer, uvea (vascular layer). It controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humor into Schlemm's canal. It also changes the shape of the lens within the eye but not the size of the pupil which is carried out by the sphincter pupillae muscle and dilator pupillae. The ciliary muscle develops from mesenchyme within the choroid and is considered a cranial neural crest derivative.
In optics, optical power (also referred to as dioptric power, refractive power, focusing power, or convergence power) is the degree to which a lens, mirror, or other optical system converges or diverges light. It is equal to the reciprocal of the focal length of the device: P = 1/f. High optical power corresponds to short focal length. The SI unit for optical power is the inverse metre (m−1), which is commonly called the dioptre (symbol: dpt). Converging lenses have positive optical power, while diverging lenses have negative power.
A dioptre (British spelling) or diopter (American spelling), symbol dpt, is a unit of measurement with dimension of reciprocal length, equivalent to one reciprocal metre, 1 dpt = 1 m−1. It is normally used to express the optical power of a lens or curved mirror, which is a physical quantity equal to the reciprocal of the focal length, expressed in metres. For example, a 3-dioptre lens brings parallel rays of light to focus at metre. A flat window has an optical power of zero dioptres, as it does not cause light to converge or diverge.
La modélisation numérique des solides est abordée à travers la méthode des éléments finis. Les aspects purement analytiques sont d'abord présentés, puis les moyens d'interpolation, d'intégration et de
Delves into the resolution power of the human eye and how it distinguishes between sources, with a practical application yielding a minimum resolution distance of 820 meters.
Delves into the resolution power of the human eye and how it distinguishes between sources, with a practical application yielding a minimum discernible distance of 820 meters.
Covers the principles and applications of Optical Coherence Tomography in various fields, including medical diagnostics and materials science.
Designing architectural façades that allow sufficient daylight to create visually comfortable and pleasantenvironments is a challenging aspect of building design. It requires accounting for visual comfort anddiscomfort glare risks and understanding the fac ...
EPFL2023
, ,
Human embryonic stem cell-derived retinal pigment epithelial cells (hESC-RPE) are a promising cell source to treat age-related macular degeneration (AMD). Despite several ongoing clinical studies, a detailed mapping of transient cellular states during in v ...
CELL PRESS2022
, ,
Designing architectural façades that allow sufficient daylight to create visually comfortable and pleasant envi- ronments is a challenging aspect of building design as it requires to account for visual comfort and discomfort glare risks, and understand the ...