What are refractive errors?
In order for our eyes to be able to see, light rays must be bent or refracted by the cornea and the lens so they may focus on the retina, the tissue that lines the back of the eye. The retina receives the pictures formed by these light rays and sends the image to the brain through the optic nerve.
A refractive error means that the shape of the eye does not refract the light properly, resulting in a blurred image. Intervention in the form of glasses, contact lenses, or refractive surgery is needed to alter the light rays and make them focus on the retina properly. Although refractive errors are called eye disorders, they are not diseases.
What are the different types of refractive errors?
A myopic eye is longer than average or has a cornea that is too steep, causing the light rays to focus in front of the retina. Close objects appear clear, but distant objects are blurred. Myopia may be inherited and is often discovered in children between 8 and 12 years old. During school-age years, when the body grows rapidly, myopia may increase. Between the ages of 20 and 40, however, there is usually little change.
Patients with high myopia have an increased risk of retinal detachment due to the eye’s longer shape. Your eye doctor should discuss this risk with you, along with the warning signs of a retinal detachment. Having LASIK or another refractive procedure will not reduce this risk, as the eye remains elongated after surgery. It is important to have regular eye examinations to monitor for any changes in the retina.
A hyperopic eye is shorter than average or has a cornea that is too flat, causing the light rays to focus beyond the retina. Near objects appear blurred, and sometimes distant objects are blurred as well. Like myopia, hyperopia is often inherited. Babies and young children tend to be slightly hyperopic, but as the eye grows longer, hyperopia lessens. This is why some people wear reading glasses as a young child then grow out of them as they get older.
Astigmatism refers to an irregular shape of either the cornea, the clear covering on the front of the eye, or of the lens inside the eye. This irregular curvature causes light to focus improperly on the retina, and vision may become blurred at any distance. Astigmatism is very common, and most people have some degree of astigmatism. Slight amounts may not affect vision, but larger amounts may cause blurred or distorted vision, eye fatigue, and headaches. Astigmatism is often inherited and present at birth, though it may change over time. It is possible to have astigmatism combined with hyperopia or myopia.
Presbyopia occurs when the natural lens inside the eye loses its flexibility, making it difficult to focus on objects up close. This is a gradual process that takes place over many years, though presbyopia usually becomes noticeable in the early to mid-40s. Presbyopia is a natural part of the eye’s aging process and cannot be prevented. It may be combined with other refractive errors, including myopia, hyperopia, or astigmatism.