The virtual prism represents the decentration component of the first-order term in a Fourier series of the corneal refractive power.

The aim of this study is to prove that the first-order term in a Fourier series of the corneal refractive power, a decentration component, is identical to a prismatic refractive component. A model using a thin round wedge prism, similar to one of the Risley prisms, is constructed. The prismatic refractive power PDφ at an angle φ in an arbitrary oblique section is formulated using geometrical optics. The discrete Fourier transform is applied to data calculated from complex equations for prisms made of glass or corneal tissue to approximate this relationship based on the amplitude, frequency, and initial phase. The approximated equation is represented by PDφ ≈ -|PD0|⁎cosφ, where |PD0| is the nominal power of the prism, which is identical to the first-order term in the Fourier series of the corneal refractive power. I term the prism with this power profile the virtual prism. These results prove that corneal refractive power has a prismatic refractive component, which is the first-order term in the Fourier series of the corneal refractive power. These findings suggest that strabismus of corneal origin exists and that the decentration component, a type of aberration that was previously thought to be uncorrectable, can be treated with some methods.