The importance of the relationship between the position of the correcting lens principal planes (H'1-H'2) and principal planes (H1-H2) of the optical eye system--aphakic correction.

In the clinical refraction of the eye, aniseikonia and anisometropia are inevitably used terms. Image formation and its retinal size is the function of the power of the dioptric eye system. However, the correcting lens in front of the eye and the eye optical system represent a unique optical afocal system, in which the distance between correcting lens and corneal vertex is of utmost importance, since it determines the size (together with appropriate correcting lens) of the retinal image. In the case of a monoculus, the size of the retinal image is not important. But, when correcting one eye while the other is emmetropic, it is important to correct it in the way that the image of the corrected eye does not produce considerable aniseikonia as a consequence of anisometropia. The authors hereby present mathematical calculation proving that if the principal point of the correcting lens P'2 is in the F1 of the emmetropic eye, meaning that? is equal to the front focal length of the emmetropic eye, there is no change in the refractive eye system, i.e. it becomes emmetropic and there is no change in the size of the retinal image. It means that an ideal position of the correcting lens in front of the eye guarantees no aniseikonia even in the extreme case of monocular aphakic spectacle correction.