To investigate the change in axial length (AL) in highly myopic adults using partial coherence interferometry, and to identify the factors associated with the increase in AL.

Medical records of highly myopic adults (≥ −6 diopters [D] or AL ≥ 26.0 mm) were retrospectively reviewed. The AL of each patient was measured using partial coherence interferometry at least three times over 2 years, and the yearly change in AL was calculated. Associations between age, AL, choroidal thickness, and the rate of AL change were evaluated using multiple regression analysis.

In total, 24 patients (4 males, 20 females) and 44 eyes were included in this study. The mean age was 54.9 ± 10.4 years, the initial AL was 29.335 ± 2.006 mm, the choroidal thickness was 72.7 ± 41.80 µm, the average spherical equivalent was −11.86 ± 3.85 D (−5.1~−22.0 D), and the mean follow-up period was 2.2 ± 0.5 years. A significant increase in AL of ≥0.05 mm was observed in 38 eyes (86.4%) at 2 years. The mean AL was significantly increased, to 29.409 ± 2.007 mm ( p < 0.001), at 1 year and to 29.476 ± 2.028 mm ( p < 0.001) at 2 years. The average rate of AL change was 0.071 ± 0.049 mm (−0.01~0.19 mm) per year. None of the included factors showed an association with the rate of AL change in multiple regression analysis.

In this study, an increase in AL in highly myopic adults was more frequent than in previous reports using A-scan. Periodic measurements are therefore recommended for the early detection of complications.