We developed a new dichoptic training method for amblyopia using polarising films. When two sheets of polarising film are stacked to create a perpendicular absorption axis, only the overlapping portion of the polarising film prevents light from passing through and occludes the vision (Fig. 2). One sheet of polarising film was attached to the target used for the training; the target was not limited to electronic devices such as televisions and tablet terminals, but also included paper media such as picture books. Using a clip, another polarising film with the absorption axis rotated 90°was attached to the training glasses on the side of the patient’s healthy eye (Fig. 3). As a result, the healthy eye was unable to see the portion to which the polarising film was attached at the target, which could only be seen with the amblyopic eye (Fig. 4). This method therefore made dichoptic training for amblyopia easy and affordable without limiting the targets that could be used. For each patient, one polarising film attached to eyeglasses and five polarising films of different sizes attached to the target were provided (60 × 106 cm, 40×71 cm, 30×53 cm, 20×36 cm, and 7x12 cm). If the size of the polarising film did not fit, the patient was instructed to cut and attach the polarising film according to the fit.
The study included patients diagnosed with anisometropic amblyopia visiting our hospital between April 2019 to April 2021. The following selection criteria were applied: patient age ≥ 3 and ≤ 8 years with anisometropia of at least 2.00 diopter at equivalent spherical power under accommodation paralysis and a maximum visual acuity of a logMAR value of 0.1 or less in the affected eye. The exclusion criteria were as follows: astigmatism of at least 1.50 diopter, heterophoria of at least 15Δ, strabismus, a history of amblyopia treatment, and difficulty in performing the examination. This study was approved by the Ethics Review Board of Kitasato University School of Medicine/Hospital and was performed in accordance with the tenets of the Declaration of Helsinki. Informed consent was obtained from all participants and a legal guardian. The participants underwent either occlusion therapy using an eye patch or dichoptic training for amblyopia using polarising films and were free to choose between the two methods.
Training for amblyopia using eye patches (eye patch group) was performed on 34 of the 58 participants (4.7 ± 0.1 years, 3–7 years). In addition, dichoptic training for amblyopia using polarising films (polarising film group) was performed in 24 cases.
All patients were instructed to use fully refraction-correcting spectacles prescribed for accommodation paralysis with cyclopentolate hydrochloride. The eye-patch group was instructed to undergo occlusion therapy using an eye patch for two hours per day. During the training for amblyopia, there were no restrictions on watching videos, reading books, or playing other games. The polarising film group was instructed to undergo dichoptic training for amblyopia using polarising films for two hours per day. During the training for amblyopia, the patients were instructed to watch TV, use tablet terminals and smartphones, and read books, with a poliarising film. All patients were instructed to record the duration (minutes) of training for amblyopia performed per day (adherence). We compared the visual acuity improvement two months after the start of training for amblyopia, the adherence rate [(training implementation time/training instruction time)×100] for the amblyopia training, and the correlation between visual acuity improvement and adherence rate.
The Mann-Whitney U test was used to compare the eye patch group and the polarising film group. The Kendall rank correlation coefficient was used to correlate the visual acuity improvement values with the adherence rate. The normality of the data was confirmed using the Kolmogorov-Smirnov test. Statistical significance was set at P < 0.05.