Canadian Medical Guide > Diseases > Eye Diseases > Refractive Errors Terms and Definitions

Refractive Errors

Medical Definition:	Deviations from the average or standard indices of refraction of the eye through its dioptric or refractive apparatus.
Guide Notes:	deviations from standard refraction of eye; DF: REFRACTIVE ERR
Also Called:	Ametropia

Refractive Errors Categories.

	Aniseikonia - A condition in which the ocular image of an object as seen by one eye differs in size and shape from that seen by the other.
	Anisometropia - A condition of an inequality of refractive power of the two eyes.
	Astigmatism - Unequal curvature of the refractive surfaces of the eye. Thus a point source of light cannot be brought to a point focus on the retina but is spread over a more or less diffuse area. This results from the radius of curvature in one plane being longer or shorter than the radius at right angles to it. (Dorland, 27th ed)
	Hyperopia - A refractive error in which rays of light entering the eye parallel to the optic axis are brought to a focus behind the retina, as a result of the eyeball being too short from front to back. It is also called farsightedness because the near point is more distant than it is in emmetropia with an equal amplitude of accommodation. (Dorland, 27th ed)
	Myopia - A refractive error in which rays of light entering the eye parallel to the optic axis are brought to a focus in front of the retina, as a result of the eyeball being too long from front to back. It is also called nearsightedness because the near point is less distant than it is in emmetropia with an equal amplitude of accommodation. (Dorland, 27th ed)
	Presbyopia - The normal decreasing elasticity of the crystalline lens that leads to loss of accommodation.

Refractive Errors Medical Definitions and Terms

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