eye disorders
Overview of Refractive Disorders
Causes of Refractive Disorders
The lens and cornea may not bend light rays to focus them on the retina correctly for several reasons. Nearsightedness(myopia) occurs when the eyeball is too long for the refractive power of the cornea and lens. Because of the corneal curvature and relatively long size, light is focused in front of (rather than directly on) the retina, and the person has trouble clearly seeing distant objects. In children, nearsightedness frequently increases until children stop growing. Farsightedness(hyperopia) occurs in some people when the eyeball is too short for the refractive power of the cornea and lens. Because of the relatively short size, light is focused behind the retina. Children and young adults who are mildly farsighted may be able to see clearly if their lens is flexible enough to properly refocus light on the retina. However, with aging, the lens stiffens. Thus, as farsighted adults age, seeing near objects clearly becomes more difficult and seeing distant objects also becomes more difficult. Blurring of nearby objects is worse in dim light. What Is Astigmatism? None Inanisometropia,people have a significant difference between the refractive errors of the eyes. Presbyopiaoccurs as people age. As people reach their early or mid 40s, the lens becomes increasingly stiff. The lens does not change shape easily, so it cannot focus on nearby objects. Thus, as adults age, they often notice difficulty seeing nearby objects. is the absence of a lens resulting from a birth defect, eye injury, or eye surgery for removal of a cataract. If a person has had a lens removed to treat Cataract but has not had a lens implant, objects look blurred at any distance. 