Nearsightedness or Myopia is a vision condition in which near objects are seen clearly, but distant objects do not come into proper focus. Nearsightedness occurs if your eyeball is too long or the cornea has too much curvature, so the light entering your eye is not focused correctly.
Minus lenses, which have thicker edges and thin centers, are used to correct nearsightedness. In addition to the regular benefits of AR, the coating is recommended because it makes the edges appear thinner.
Hyperopia, also known as farsightedness or long-sightedness, is a defect of vision caused by an imperfection in the eye (often when the eyeball is too short, cornea is too flat or when the lens cannot become round enough), causing an inability to focus on near objects or close reading, and in extreme cases causing a sufferer to be unable to focus on objects at any distance. As an object moves toward the eye, the eye must increase its power to keep the image in focus on the retina.
Plus lenses are used to correct farsightedness and are thicker in the center and thinner of the edges. An AR coating is recommended to reduce the appearance of magnification.
Astigmatism is a vision condition that causes blurred vision due either to the irregular shape of the cornea, the clear front cover of the eye, or sometimes the curvature of the lens inside the eye. An irregular shaped cornea or lens prevents light from focusing properly on the retina, the light sensitive surface at the back of the eye. As a result, vision becomes blurred at any distance.
Lenses with a "compound prescription" are used to correct astigmatism. These lenses have a spherical power to correct nearsightedness or farsightedness, and a cylinder power to correct the blurriness caused by astigmatism.
Presbyopia is a vision condition in which the crystalline lens of your eye loses its flexibility, which makes it difficult for you to focus on close objects.Symptoms of Presbyopia are difficulty reading fine print, particularly in low light conditions, eyestrain when reading for long periods, blur at near or momentarily blurred vision when transitioning between viewing distances.
Presbyopia is generally corrected with progressive lenses, lined bifocal lenses, trifocal lenses, or simple reading glasses.
Because the effects of Presbyopia continue to change the ability of the crystalline lens to focus properly, periodic changes in your eyewear may be necessary to maintain clear and comfortable vision.