Progression pattern of non-amblyopic Anisomyopic eyes compared to Isomyopic eyes

This study aimed to determine the progression pattern of non-amblyopic anisomyopic children from ages 6 to 16 years. This retrospective study analyzed the electronic medical records of 8680 myopic children who visited Sankara Nethralaya, Chennai, India over eight years (2009 to 2017). A total of 711 records were retrieved based on inclusion criteria. In addition, 423 records out of 711 had consecutive follow-up for three years (baseline plus three follow-up visits) and were considered to determine the progression pattern. The cycloplegic sphero-cylindrical refraction was taken for analysis and converted to vector notation of M (SE), J0, and J45. Anisomyopia referred to the interocular difference of myopic SE of ≥ 1 D whereas isomyopia referred to the interocular difference of myopic SE of < 1 D. Based on the refraction of the less ametropic eye, anisomyopes were further categorized into bilateral anisometropic myopia (BAM) and unilateral anisometropic myopia (UAM). The isomyopic cohort showed a mean annual progression of -0.49 ± 0.54 D (median [IQR] -0.38 D [{-0.75}-0.00]). In BAM, the mean annual progression of the more myopic eye was -0.45 ± 0.55 D (median [IQR] -0.38 D [{-0.75}-0.00]), and the less myopic eye was -0.37 ± 0.55 D (median [IQR] -0.25 D [{-0.63}-0.00]). This difference was significant (t (212) = -2.14, p < 0.05). In UAM, the myopic eyes (-0.39 ± 0.51 D; median [IQR] -0.25 D [{-0.75}-0.00]) showed a statistically significant higher mean annual progression compared to emmetropic eyes (-0.22 ± 0.36 D; median [IQR] 0.00 D [{-0.44}-0.00]; t (96) = -3.30, p < 0.001). In terms of progression trend, in the BAM group, the rate of change of mean SE between the more myopic and the less myopic eyes were similar (-1.12 ± 1.20 D; median [IQR] -1.13 D [{-2.00}-{-0.38}] vs. -1.05 ± 1.25 D; median [IQR] -0.88 D [{-1.75}-{-0.13}]; t (138) = -0.64, p > 0.05). However, the more myopic eyes of UAM showed a higher myopic trend compared to the emmetropic eyes (-1.37 ± 1.06 D; median [IQR] -1.32 D [{-2.13}-{-0.50}] vs. -0.96 ± 1.11 D; median [IQR] -0.75 D [{-1.56}-{-0.25}]; t (61) = -2.74, p < 0.05).   Conclusion: Children with BAM and UAM eyes exhibit different progression patterns from each other. While the rate of the refractive shift in myopic eyes of UAM is similar to isomyopic eyes, BAM eyes present a slower rate of progression than isomyopic eyes. What is Known: • The rate of change of refraction in anisomyopes is higher compared to isomyopic children. • Less myopic eyes tend to shift towards more myopia while more myopic eyes show stable refraction. What is New: • The progression pattern of bilateral anisometropic myopia and unilateral anisometropic myopia differ from one another. • While the rate of the refractive shift in myopic eyes of unilateral anisometropic myopia is similar to isomyopic eyes, bilateral anisometropic myopia eyes present a slower rate of progression than isomyopic eyes. • The pattern of change in the interocular difference of anisometropia depends on the laterality (bilateral or unilateral ametropia), and degree of spherical equivalent in the more ametropic eye.