دانلود کتاب The Artisan lens: effects on vision quality, the corneal endothelium and vision-related quality of life

Refractive errors are the most frequent disorders of the eye. In the ideal refractive state, emmetropia, an image is focused directly on the retina, resulting in the perception of a sharp image in a healthy visual system. Such eyes do not require glasses or contact lenses to see sharply. Most eyes, however, have some degree of refractive error, although correction is not always required. In myopia (nearsightedness), the image appears focused anterior to the retina, producing a sharp image at near and a blurred image at distance. A concave lens (minus Diopter) is required to sharpen the image. The reverse is true in hypermetropia (also known as hyperopia or farsightedness), where the image is projected posterior to the retina, producing a blurred image at near and a sharper image at distance. A convex lens (plus Diopter) is required to produce a clear image. Astigmatism (cylindrical error) is the result of two different refractive powers between two perpendicular meridians. A cylindrical correction can correct this problem. Extreme cases of all these refractive errors can cause severe visual loss. Anisometropia is the presence of two significantly different refractive errors. In these situations, simple spectacle correction is not always suitable due to aniseikonia (different sized images) resulting from the different powers in the lenses; other options such as contact lenses or surgery can then be considered. When refractive errors and anisometropia are not corrected aptly, diminished binocular vision and/or amblyopia could result.  Read more...