| Myopia (nearsightedness) means that the eye is too long for the focusing power (curvature) of the cornea, such that light rays are bent too much and therefore focused in front of the retina. The light rays continue onto the retina where they form a blurry image. |
Hyperopia (farsightedness) means that the eye is too short for the focusing power of the cornea, such that light rays are not bent enough and therefore focused behind the retina (if that were actually possible). Light rays arriving at the retina are not yet focused so they form a blurry image. Symptoms of hyperopia often do not show up until later in life. In youth, the up-close focusing mechanism (accommodation) is used to bend the light rays more and thus make the vision clear. With aging, accommodation fatigues and the blurriness from hyperopia will then become apparent. |
Astigmatism usually results from the cornea being shaped more like part of a football rather than part of a basketball, so that incoming light rays are focused at multiple points in the eye rather than on the retina; at the plane of the retina, they’re almost all out of focus. Astigmatism is often combined with myopia or hyperopia. |
Presbyopia (the need for reading glasses) will ultimately affect everyone due to the loss of accommodation as a result of the decrease of lens flexibility that occurs with aging. With presbyopia, the vision up close becomes blurry and usually requires people aged 40 and older to wear bifocals or reading glasses (or if they are a little nearsighted, take off their glasses and use their nearsightedness to read). Since vision correction surgery cannot reverse this aging process, presbyopia cannot be directly corrected surgically. However, there are surgical and non- surgical techniques available which can effectively reduce symptoms associated with presbyopia. |
