Knapp’s Law states that a lens placed before an eye with axial ametropia will produce an image that is the equivalent of an emetropic eye. A contact lens, on the other hand, will create magnification, which would be desirable for the treatment of refractive aniseikonia. However Knapp’s Law is imperfect and many feel that it’s not quite appropriate for actual clinical use. It’s difficult to tell whether the ametropia is completely axial or refractive, or a combination of the two. Knapp’s Law does also not apply to aniseikonia caused by the layout of the retina’s receptors.

In an attempt to help equalize image size, a style of lens fabrication is used to create an iseikonic lens. In the design of an iseikonic lens, the magnification can be manipulated without affecting the lens’ refractive power. The determining factors in spectacle magnification are 1) base curve 2) vertex distance 3) thickness. With these three factors, the designer can adjust each of these values to determine the best design. But first we must determine the difference in image size.

http://www.opticourier.com/1webmagazine/2006/02feb/content/lens_corner/index.asp

this gives us an idea to have different base curve and thickness (vertex distance can't be differ from two lenses as they are on the same frame) between two lenses can gives Tom equal image size in both eyes. So.. that's what we can do to treat his aniseikonia...