  A large-scale labeled dataset is a key factor for the success of supervised
deep learning in computer vision. However, a limited number of annotated data
is very common, especially in ophthalmic image analysis, since manual
annotation is time-consuming and labor-intensive. Self-supervised learning
(SSL) methods bring huge opportunities for better utilizing unlabeled data, as
they do not need massive annotations. With an attempt to use as many as
possible unlabeled ophthalmic images, it is necessary to break the dimension
barrier, simultaneously making use of both 2D and 3D images. In this paper, we
propose a universal self-supervised Transformer framework, named Uni4Eye, to
discover the inherent image property and capture domain-specific feature
embedding in ophthalmic images. Uni4Eye can serve as a global feature
extractor, which builds its basis on a Masked Image Modeling task with a Vision
Transformer (ViT) architecture. We employ a Unified Patch Embedding module to
replace the origin patch embedding module in ViT for jointly processing both 2D
and 3D input images. Besides, we design a dual-branch multitask decoder module
to simultaneously perform two reconstruction tasks on the input image and its
gradient map, delivering discriminative representations for better convergence.
We evaluate the performance of our pre-trained Uni4Eye encoder by fine-tuning
it on six downstream ophthalmic image classification tasks. The superiority of
Uni4Eye is successfully established through comparisons to other
state-of-the-art SSL pre-training methods.
