Topical Review: Retinally Induced Aniseikonia.

SIGNIFICANCE: We review retinally induced aniseikonia, an underrecognized condition resulting from common retinal conditions that has a significant effect on quality of life. Optometrists can influence the timing of surgical intervention to mitigate the damage from delaying surgical intervention in patients whose other findings do not meet a surgeon's treatment threshold.Aniseikonia due to optical differences between the eyes occurs in 1 to 3.5% of the population and can hinder the quality of binocular vision. The less noted retinally induced aniseikonia is due to mechanical distortion and displacement of the retinal photoreceptors and occurs with disorders such as epiretinal membrane, reattached retinal detachment, macular hole, and macular edema. Despite that it was first reported in 1950 and its incidence continues to rise in the aging population, many eye care practitioners are unaware of this condition, which can persist or even be exacerbated after treatment as a contributing cause of binocular vision symptoms. The purpose of this report is to allow more eye care practitioners to become familiar with retinally induced aniseikonia. The review of the literature includes demographics and epidemiology, etiology, pathogenesis, diagnosis, results of treatment, prognosis, and case examples.

The influence of aniseikonia on the VEP by random-dot stereogram.

Static random-dot stereograms were employed to evaluate the unequal input between two eyes, both objectively by VEP and psychophysically. In subjects with normal binocular function, different levels of artificial aniseikonia (from 2% to 15%) were established by placing several levels of size lenses in front of one eye. Binocular summation in amplitude in the VEP was observed below 5% aniseikonia, and the binocular inhibition took place above 5% aniseikonia. Psychophysically, perception of stereopsis could be maintained between 3% and 5% aniseikonia, but disappeared above 5% aniseikonia. Electrophysiological findings of binocular interaction caused by aniseikonia corresponded to the psychophysical findings, and stereoscopic perception was obtained only in the case of binocular summation in the VEP. In the present study, the amount of tolerable aniseikonia in order to maintain stereopsis was considered to be below 5%.

Horopter shifts due to a magnification change.

Both the equidirection ( nonius ) and the equidistance horopter criteria were used on a group of subjects with and without the application of a 5% overall magnifier before the right eye. For three of six subjects, shifts in the equidirection horopter induced by this afocal lens could not be predicted on the basis of the magnification properties of the lens and the assumption that corresponding points are fixed. Equidistance horopter plots showed reasonably systematic reductions in slope between the predicted and the measured values for all subjects. Irregularities in all data were accounted for by shifts in the vergence angles during the experiment.

Meridional size disparity as a function of compressed inferior visual space: a case in point.

This case report describes a very unusual form of aniseikonia which was eventually documented to be variable within the total field of vision and limited to vertical space perception. Initially the condition could be partially relieved by monocular occlusion, visual training procedure, and the use of isoikonic lenses. Ultimately, the greatest improvement was produced by the introduction of prismatic properties to the lenses which directly addressed the patient's problem of meridional space perception.