Refraction of the eye along any line except the visual axis (or line of sight) therefore representing the refraction of any extrafoveal region. Example: if an eye is emmetropic along the visual axis, at 40 degrees of temporal retinal eccentricity the allometropia will be about plano −2.50 ✕ 90º and at 50 degrees, +0.50−3.50 ✕ 90º. See oblique astigmatism.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann