If monofocal cataract surgery has been performed on the first (dominant) eye with a +12.0 dioptres IOL implanted, what should be the dioptres for the other eye, for an overall optimum refractive outcome?

Your question does not, unfortunately, supply enough information for a meaningful response. It is certainly understandable to want to think of the eye as a "camera" that uses a lens of a particular power (prescription) as in glasses or contact lenses, to achieve an optimal focus post-operatively. But the eye is not a camera. Setting aside for the moment the issues of pupil size, contrast sensitivity, and presbyopia, it is useful to realize that the eye has two anatomically distinct "lenses:" the natural lens that has clouded up (the cataract) and the other, more important and stronger one: the cornea.

The 1) curvature (i.e. focusing power) of the cornea, 2) the distance from the front to the back of the eye, 3) the pre-op glasses prescription, and the 4) distance between the cornea and the natural lens are all important variables that need to be measured and entered into a regression analysis formula to determine the ideal power for the new IOL.

_Written by J. Trevor Woodhams, M.D. - Chief of Surgery, Woodhams Eye Clinic