What Are Refractive Errors?
Refractive error means that the shape of your eye does not bend light correctly, resulting in a blurred image. The main types of refractive errors are myopia (nearsightedness), hyperopia (farsightedness), presbyopia (loss of near vision with age), and astigmatism.
Myopia (nearsightedness) is a most common vision condition , where near objects can be seen clearly than distance objects and can be corrected easily using prescription glasses especially designed to counter act the effect. A concave lens (minus powered) is placed in front of a myopic eye, bending the light to refract properly on retina to clarifying the vision.
Hyperopia (farsightedness) is less common vision condition where distant objects may be seen more clearly than near objects, hyperopic person may experience symptoms differently some people may not notice any problems with their vision especially when they are young. It can be corrected by a convex lens (plus powered) by placing it in front of a hyperopic eye, diverging light to focus properly.
Astigmatism is common and usually minor vision condition that caused blurred or distorted vision, it occurs when the cornea or crystalline lens isn’t perfectly curved shape, many people who wear glasses have some degree of astigmatism. It can be corrected by a compound convex or concave lens by placing it in front of a astigmatic eye, lining up light on both meridians.
Presbyopia is a natural part of aging process and caused by changes to the lens inside the eye ball. As people age, the lens became harder and less elastic making it more difficult for the eye to focus on close objects. It is a type of refractive error along with myopia, hyperopia and astigmatism. It can be corrected using single vision, bifocal and progressive lens.