Refraction defects, known as eye disorders among the people, are visual disorders that occur as a result of the inability of the image to focus on the retina-retina layer. They can be corrected with glasses, contact lenses, laser methods and various surgeries.

In order for our eyes to see clearly, the rays coming into the eye must be refracted (refraction) and focused on the retina at the back of the eye, called the retina. This refraction of light is provided by the cornea (the outermost transparent layer of the eye) and the lens (the lens of the eye). If the eye can focus rays coming from different distances on the retina, the refractive function of the eye becomes normal and this condition is called emmetropia . In eyes with refractive errors, the rays cannot focus on the retina and a blurred or distorted image occurs.