Dynamic aniseikonia measurement: prismatic effect appears on the hess chart.
PURPOSE: To determine if aniseikonia appears on the Hess [Screen] Chart and if it can be measured thereby; and to compare such measurement to the standard Awaya New Aniseikonia Test in both artificial and pathologic aniseikonia. SUBJECTS AND METHODS: Twenty normal subjects with 20% artificial induced aniseikonia (Group 1) and 21 patients with pathologic aniseikonia (Group 2) were examined with the New Aniseikonia Test (NAT) and the Hess Chart. Group 2 was divided into three subgroups: Group 2-1, 13 patients with aphakia, whose operated eyes were more hypermetropic that their better eyes; Group 2-2, 3 patients with myopic anisometropia more than 5 diopters; and Group 2-3, 5 patients who had received macular translocation surgery (MTS). RESULTS: In normals, measurement of the 20% artificial aniseikonia ranged from 10% to 21% (mean 15%) using the NAT, and from 16% to 39% (mean 27.1% vertically and 24.6% horizontally) using the Hess Chart. In the 21 patients with pathologic aniseikonia, the NAT measurements ranged from 0% to 24% (upper limit of the NAT) and the Hess Chart measurements ranged from 0% to 65%. A large amount of the aniseikonia that appeared on the Hess Chart disappeared or was significantly reduced by changing the spectacle correction to a contact lens or intraocular lens. CONCLUSION: The aniseikonia that appeared on the Hess Chart was dynamic aniseikonia, due to rotational magnification inherent and unavoidable in the execution of the aniseikonia measurement on the Hess Chart. Aniseikonia, not due to refractive errors brought on by retinal surgery such as MTS, is difficult to correct with iseikonic lenses or other optical means.