A computer-assisted method of calculating intraocular lens (IOL) power using formulas according to Gaussian optics is described. The method is more exact than current theoretical formulas, especially in calculating corneal power and in dealing with principal planes, and tends to give somewhat higher values for IOL power. One advantage of the theoretical approach is that the eye can be analyzed optically in a conventional manner, not only for the IOL power of emmetropia but also for the power of the biological lens, the total refractive power of the eye, and the magnification of the entire system. The relation to other theoretical formulas is discussed.