When the eye does not provide the correct amount of power for its size, more specifically the axial length, a refractive error results. When the eye provides too much power, the person is nearsighted or myopic. When the eye does not provide enough power, then the person is farsighted or hyperopic. If you are still confused it may help you to know that the eye requires more power to see things at near so an eye with too much power (myopic) would see things better at near, while an eye with too little power (farsighted) would see better at far. People who are nearsighted (eye is too strong) have spectacle lens prescriptions that start with a minus (-) sign. Their glasses subtract power from the optical system of the eye. For farsighted or hyperopic patients, the opposite is true. Their prescriptions start with a plus (+) sign because they must add power to an eye that is optically weak.
This term denotes the specific optical character of the eye. The eye is like a camera. The focusing elements of the eye are the cornea and the lens. The film is the retina. When light enters the eye it is bent by the cornea and the lens and focused on the retina (film) to create a clear image. If light is not exactly focused on the retina due to a mismatch in the power of the cornea and lens, a blurred image results. Eyeglasses are an optical device used to correct this defocused image. The following terms describe the various refractive states of the eye: Emmetropia, Myopia, Hyperopia, Astigmatism.
Deviations from the average or standard indices of refraction of the eye through its dioptric or refractive apparatus.
Vision problems caused by an imperfect optical system, most commonly myopia, hyperopia and astigmatism.
Eye problems which can be corrected through glasses, contact lenses, or, in some cases, surgery.
hyperopia, myopia, and astigmatism.
Astigmatism, farsightedness, and nearsightedness that can be helped with prescriptive glasses.
imperfections in the focusing power of the eye.