Clinical Aniseikonia in Anisometropia and Amblyopia

Abstract

Purpose: Clinically, aniseikonia (a perceived difference in shape and image size between the eyes) is often neglected in anisometropic amblyopia due to assumed measurement difficulties. Therefore, we currently lack evidence on whether correction of aniseikonia is beneficial. This study aimed to determine whether subjective aniseikonia is measurable in anisometropia with or without amblyopia. Methods: Participants (15-52 years) with Anisometropic Amblyopia (n = 7), Anisometropia without amblyopia (n = 6) and Isometropic Controls (n = 6) were recruited. Subjective aniseikonia was measured using three clinical techniques: Robertson Technique (RT) (penlight and Maddox rod), Aniseikonia Inspector Version 3 (AI3), and the New Aniseikonia Test booklet (NAT), and a psychophysical adaptive method, the Contrast-balanced Aniseikonia Test (CAT), where dichoptic contrast adjustments compensate for any suppression. Results: Eighteen participants completed all tests, one Anisometropic Amblyopia participant could only complete the CAT and NAT due to fusion loss. The Anisometropic Amblyopia group exhibited the most aniseikonia (range-1.50-+10.50%) followed by Anisometropic Controls (range-3.30-+4.50%) and Isometropic Controls (range-1.50-+3.28%). There was a significant trend of more subjective aniseikonia with increasing amounts of anisometropia across all four tests (AI3 r = 0.630, p = 0.005; NAT r = 0.542, p = 0.017; RT r = 0.499, p = 0.035; CAT r = 0.440, p = 0.059. Bland Altman analysis demonstrated clinically significant levels of variability between the tests. Conclusions: Subjective aniseikonia can be reliably measured in patients with anisometropia and suppression. Subjective aniseikonia measurement is recommended as four of the most commonly used clinical tests did not support the 1% per dioptre rule of thumb.

Evaluation of Aniseikonia in Patients with Successfully Treated Anisometropic Amblyopia Using Spatial Aniseikonia Test

“…This finding supports the optical approximation and empirical rule of 1% aniseikonia per 1.00D of anisometropia [1,[42][43][44][45]. In contrast, other earlier studies reported that aniseikonia per 1.00 D of anisometropia was less than 1.0%/D [20,46]. These earlier studies evaluated aniseikonia using direct comparison methods, such as New Aniseikonia Tests (HANDAYA Inc., Tokyo, Japan) and Aniseikonia Inspector (Optical Diagnostics, Culemborg, The Netherlands).…”

“…The direct comparison method underestimates aniseikonia because of the influence of peripheral fusion and sensory adaptation to cancel out image differences caused by aniseikonia in binocular vision [24][25][26][27]. South et al showed that the amount of aniseikonia in the patients with anisometropic amblyopia had significant variation [20]. Moreover, El-Abedin Rajab et al reported that the direct comparison method in axial anisometropia did not produce indications of significant aniseikonia [47].…”

“…Previously, patients with anisometropic amblyopia hardly complained of anisometropic symptoms because of the effects of adaptation and suppression in the cerebral cortex [3]. South et al reported that patients with anisometropic amblyopia perceived aniseikonia with significant variety; the amount of aniseikonia also varied significantly [20]. This result can be considered to have two causes.…”

Measuring aniseikonia and investigating neuroplasticity and image factors in amblyopia (MAGNIFY): study protocol for a randomised clinical trial

“…Aniseikonia is likely to be present in those with anisometropic amblyopia [ 27 , 28 ]. The difference in images sizes could potentially hinder binocular vision.…”

The development of active binocular vision under normal and alternate rearing conditions

“…Since little is known about the effects of aniseikonia on visual development or the potential benefits of correction (South et al, 2020), we conducted a series of experiments to simulate the effects of aniseikonia. We achieve this by simply scaling up the right image by a certain factor and cutting the edges so left and right images retain the same size.…”