OCT-based myopic index: a biological predictor for the progression of high myopia

BACKGROUND: The growth of axial length (AL) can lead to high myopia and ocular deformation, especially causing microstructural changes in the fundus, which cannot be fully quantified by AL alone. We propose an optical coherence tomography (OCT)-based modified AL (Myopic Index) to represent the extent of fundus deformation caused by AL elongation and to explore its clinical significance in myopic progression prediction. METHODS: A deep learning model was trained using 27 539 cases of OCT images and referred ocular biometric data to evaluate the Myopic Index. By comparing the Myopia Index with the Measured AL, the difference of two AL indices (DAL) was calculated. We further prospectively employed 2866 cases of OCT images, which were categorised into short AL (Measured AL<22 mm), normal AL (22 mm≤Measured AL<26 mm) and long AL (≥26 mm), to evaluate the model ability of myopic progression prediction. The attention regions of images were also analysed. RESULTS: The Myopia Index was closely correlated with Measured AL (all p<0.001, R²=0.804 in all eyes). Specifically, the Myopia Index was closer to the Measured AL in eyes with long ALs, whereas in eyes with short and normal axial lengths, the Myopia Index clustered around 23-24 mm. The visualisation model demonstrated that for eyes with short and normal ALs, attention regions were primarily concentrated on the retina; conversely, for eyes with long ALs, the choroidal layer and the retinal pigment epithelium layer received more attention. Moreover, DAL was significantly correlated with AL increment (p=0.038). CONCLUSIONS: The Myopia Index reflects the real status of fundus microstructures through fundus microstructures, with a particular focus on the choroid. The Myopia Index demonstrates good predictive capabilities for high myopia progression.