Helmholtz's Light Refraction Accommodation Theory
One of the most known theories that explain the mechanism of accommodation is the theory of Hermann Helmholtz which was introduced in 1855. According to his theory, light refraction, getting on a retina, is carried out through a crystalline lens. It is composed of fibers. It depends on it what subject will be visible legibly. Not only the crystalline lens, but also radial and circular muscles regulate a crystalline lens tension. The crystalline lens is not a solid body – it’s elastic allows to change light refraction angle. It is the making component of the mechanism of a dynamic refraction. The essence of process consists that at absence on a retina of a sharp image of a subject (a poor or excessive tension of a crystalline lens); the signal …show more content…
And if the ciliary muscle is contracted, the diameter of this ring‐shaped muscle is decreased, and there is no more pulling action on the lens via the zonular fibers and therefore the focus is set to "near object". Although Helmholtz's theory has been widely accepted since 1855, its mechanism still remains controversial. Alternative theories of accommodation have been proposed by others, including L. Johnson, M. Tscherning, and Ronald A. Schachar. When the eye is viewing an object at a far distance (such that parallel rays of light are entering the eye), the ciliary muscle within the ciliary body relaxes. The ciliary processes pull on the suspensory ligaments (or zonules), which in turn pull on the lens capsule around its equator. This causes the entire lens to flatten or to become less convex, enabling the lens to focus light from the far-away object. Conversely, when the eye views an object at a near distance, an “accommodative demand” is created. As a result, the ciliary muscle works or contracts, causing tension to be released on the suspensory ligaments and, subsequently, on the lens capsule. This causes both (front and back) lens surfaces to become more convex and the eye to be able to focus at near. The ciliary fibers have circular, longitudinal (meridional) and radial
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