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

Abstract

Anisometropic amblyopia is decreased visual acuity in one eye, and treatment consists of wearing complete corrective spectacles. Aniseikonia occurs with complete correction of anisometropia using spectacles. Aniseikonia has been ignored when treating pediatric anisometropic amblyopia because of the prevailing belief that anisometropic symptoms are suppressed by adaptation. However, the conventional direct comparison method for evaluating aniseikonia significantly underestimates the degree of aniseikonia. This study investigated whether the adaptation occurs due to long-term anisometropic amblyopia treatment in patients who have had successful amblyopia treatment using a spatial aniseikonia test with high accuracy and repeatability compared with the conventional direct comparison method. The amount of aniseikonia was not significantly different between the patients with successful amblyopia treatment and individuals with anisometropia without a history of amblyopia. In both groups, the aniseikonia per 1.00 D of anisometropia and the aniseikonia per 1.00 mm of aniso-axial length were comparable. The repeatability of the amount of aniseikonia using the spatial aniseikonia test did not differ significantly between the two groups, indicating a high degree of agreement. These findings suggest that aniseikonia is not adapted to amblyopia treatment and that aniseikonia increases as the difference between spherical equivalent and axial length increases.

Keywords: amblyopia; aniseikonia; anisometropia; anisometropic amblyopia; binocular vision.

Figure 1

The spatial aniseikonia test (SAT). (a) The SAT has +8.00 D lenses built into the left and right barrels, and a monitor is built in at the focal point of the lens (125 mm). (b) Each subject viewed the targets displayed on the SAT under subjective best-corrected visual acuity with an optic lens.

Figure 2

SAT target. (a) The target consists of an oblique red line and a white vertical line on a black background. (b) In aniseikonia, the retinal image of one eye is perceived as larger than that of the other eye, the target is enlarged, and the distance between the two white vertical lines is wider than that in the absence of aniseikonia. (a′) In the absence of aniseikonia, all lines appear parallel to the frontal plane. (b′) In aniseikonia, the eye with the enlarged retinal image perceives the white vertical line as being farther away than the other eye. For example, if the image presented to the left eye appears larger than that of the right, the white vertical line of the left eye appears to recede. SAT, spatial aniseikonia test; LE, left eye; RE, right eye.

Figure 3

Amount of aniseikonia in the amblyopic and anisometropic groups. Red and blue box plots with dots indicate aniseikonia in the amblyopic and anisometropic groups, respectively. Aniseikonia was insignificantly different between both groups.

Figure 4

Aniseikonia per 1.00 D of anisometropia. Red and blue box plots with dots show aniseikonia per 1.00 D of anisometropia in the amblyopic and anisometropic groups, respectively. There were insignificant differences between both groups.

Figure 5

Aniseikonia per 1.00 mm of aniso-axial length. Red and blue box plots with dots indicate aniseikonia per 1.00 mm of aniso-axial length in the amblyopic and anisometropic groups, respectively. There were insignificant differences between both groups.

Figure 6

Relationship between aniseikonia and the difference of SE. Red and blue dots indicate the amblyopic and anisometropic groups, respectively. The solid red and blue lines indicate the regression lines for the amblyopic and anisometropic groups, respectively. Both groups showed a significant positive correlation between aniseikonia and the difference of SE. SE, subjective spherical equivalent.

Figure 7

Relationship between aniseikonia and the difference of AL. Red and blue dots indicate the amblyopic and anisometropic groups, respectively. The solid red and blue lines indicate the regression lines for the amblyopic and anisometropic groups, respectively. Both groups showed a significant positive correlation between aniseikonia and the difference of AL. AL, axial length.

Figure 8

Relationship between aniseikonia and stereoacuity. Red and blue dots indicate the amblyopic and anisometropic groups, respectively. The solid red and blue lines indicate the regression lines for the amblyopic and anisometropic groups, respectively. Both groups showed a not significant correlation between aniseikonia and stereoacuity.