Presbyopia

Firstly, presbyopia is not a refractive defect, but only a“side effect” the passing years. The parallel rays coming from infinity are diverted (refracted) from the system cornea/crystalline on a specific portion of the retina that allows the sharp vision: the macula. So an eye that can perfectly converge parallel rays coming from infinity on the macula is an eye emmetropic. In this eye has gone a harmonious and balanced development of its size and its "Refractive system" (Cornea / lens). In Italy, by custom, it is said that the eye has a visual acuity (or visual acuity) of 10/10. Nature has endowed the human eye (and many animal species) the ability to maintain focus the image of an object when it is approaching (that is, the condition of automatically varying the focus). This possibility that : accommodation, is implemented through the contraction of the crystalline (that by varying the curvature of its surfaces and becoming more or less flattened spherical allows to maintain the clarity of the images that reach the the macula. placed at different distances from this. Emmetropic eye then, that is, one whose rays are perfectly focused on the macula, theaccommodation only intervenes in near vision. In the process of accommodating the crystalline lens can vary its form (by lenticular spherical, thus changing its refractive power) by the contraction of a small muscle ring (the ciliary muscle) contracting that precisely determines the increase of the thickness of the lens. The increase of the radii of curvature of the anterior surface and posterior lens allows divergent rays, that originate from near, to be focused on the macula. This mechanism is so fast that the brain does not perceive, unless the eye does not present a significant degree of hypermetropia or until it appears with age, the loss of elasticity of the crystalline, as is the case with the Presbyopia. In fact, generally after 40-45 age, the mechanism of focus for near vision that I described (accommodation), begins to not be as efficient for progressive loss of elasticity of the lens (with the passing of the years has in fact a progressive and physiological loss of accommodative capacity by more than 10 diopters a 8 years 1 diopter in 60-65). At the beginning we realize that we need "more time" to focus in reading, then we begin to remove objects, Finally, when the arms are no longer sufficient we go to the eye doctor. The loss of elasticity of the lens makes it impossible to increase its dioptric power (its ability to take the form spherical) and to return to see clearly we need to add to the front of the eye of converging lenses (positive) such as those of’hypermetropia. The loss of elasticity over the 65 age, may begin to associate the loss of transparency of the crystalline (cataract).