Abnormalities and irregularities in the optical system of the eye might have a significant impact on the quality of vision, for example worsening of vision in the dark or dusk, double vision etc.
These are optical defects of vision (coma, spherical aberration, trefoil, quatrefoil, secondary astigmatism) that are not correctable with glasses, contact lenses, or with traditional laser surgery. Higher order aberrations can be innate or acquired. The latter develop after surgery on the cornea or lens. Acquired aberrations may also be caused by changes in the shape of the cornea or lens, vitreous opacities and changes in the retina.