Purpose. Aniseikonia has been traditionally measured using the New Aniseikonia Test (NAT) based on red/green anaglyphs. This study was designed to establish whether the NAT is a valid and reliable test.
Methods. The NAT was tested on three groups of subjects: a control group (n = 45) and two groups of participants at risk of experiencing aniseikonia, those with anisometropia greater than or equal to 1.00 D (n = 29) and those with bilateral pseudophakia (n = 26). The validity of the test was established by comparing the measured aniseikonia with that simulated with size lenses in a double-blind study. Repeatability was evaluated by comparing the results obtained at two different time points.
Results. Our results indicate that the NAT underestimates aniseikonia and more so in the horizontal than in the vertical direction. Repeatability was poor, although biases were clinically insignificant. However, the 95% limits of agreement were around ±2%. The behavior of the test was similar in the three groups of subjects.
Conclusions. We conclude that the repeatability of the NAT is not very high and recommend that clinicians be cautious when interpreting the results of this test.