Field-Dependent Aniseikonia Associated with an Epiretinal Membrane: A Case Study
Received 13 January 2005; accepted 3 October 2005. published online 12 December 2005.
Purpose
Aniseikonia is a binocular anomaly in which the two eyes perceive images of different sizes and/or shapes. It is usually assumed to be constant as a function of visual field angle (VFA) (i.e., angular distance from the line of sight). This is correct for optically induced aniseikonia, such as the aniseikonia that is associated with anisometropia and probably also pseudophakia. The purpose of this article is to show that if the aniseikonia is of retinal origin, then the aniseikonia may no longer be constant as a function of VFA (i.e., field-dependent aniseikonia).
Design
Case report, with the patient having a unilateral epiretinal membrane.
Methods
The aniseikonia was measured in vertical and horizontal directions with a customized version of the Aniseikonia Inspector software. The VFA was made variable by changing the dimensions of the comparison targets in the direct comparison procedure.
Main Outcome Measure
Aniseikonia as a function of VFA.
Results
The patient exhibited good repeatable aniseikonia, ranging from 23% to 2.5% for VFAs ranging from 0.36° to 5.7°. Higher angles had lower aniseikonia. A control subject did not show this field-dependent aniseikonia.
Conclusions
Aniseikonia may vary with VFA due to a retinal cause such as an epiretinal membrane. The problem with field-dependent aniseikonia is that it cannot be corrected fully with conventional optics, which exhibit an approximately constant magnification as a function of VFA. Nevertheless, by correcting 5% to 10% aniseikonia, which showed up in the VFA measurement range at 2° to 3°, our patient had improved visual comfort, especially for reading.
Reprint requests to Gerard de Wit, Optical Diagnostics, Eikvaren 19, 4102 XE Culemborg, The Netherlands.
Manuscript no. 2005-43.
Dr Muraki has no proprietary interest in any of the products discussed in the article. Dr de Wit is the owner of Optical Diagnostics and the developer of the Aniseikonia Inspector, the device that was modified for this research.
ABSTRACT