Understanding The 4 Refractive Errors
The eye focuses light like a camera. The cornea and lens of the eye focus light onto the macula, a part of the retina.
If an eye is too long, the image is focused in front of the macula, resulting is myopia, or nearsightedness. A nearsighted eye will have clearer vision at near than in the distance.
If the eye is too short, light is focused behind the macula, resulting in hyperopia, or farsightedness. A farsighted eye may be blurry at all distances, but distance vision is usually clearer than near.
Astigmatism results when the cornea has two different curvatures, like a football. Astigmatism degrades vision at all distances, making vision blurry at both distance and near.
Presbyopia occurs when an eye loses its ability to focus on near objects. This happens to all people by their mid-40s. Reading glasses or bifocals are commonly used to manage presbyopia.