A refractive error, or refraction error, is an error in the focusing of light by the eye and a frequent reason for reduced visual acuity (the capacity of the eye to see fine detail). The word “ametropia can be used interchangable with “refractive error”. Types of ametropia include myopia, hyperopia and astigmatism.
An eye that has refractive error when viewing distant objects is said to have ametropia or be ametropic. This eye, cannot focus parallel rays of light (light from distant objects) on the retina.
They are frequently categorized as spherical errors and cylindrical errors: