Myopia is an irreversible visual disorder. Its pathogenic mechanism is not completely determined. This lack of understanding has led to difficulties in its early detection and prevention. Herein, it is reported that the content of dopamine (DA) inside tears is related to myopia diopter. Changes in DA are detected by the use of a wearable corneal biosensor. The biosensor is prepared by electrodeposition of the enzyme tyrosinase and poly (3,4-ethylenedioxythiophene) functionalized sulfur-doped graphene onto a self-designed corneal microelectrode. This leads to a high-performance biosensor with a high sensitivity (of 12.9 ��A ����10���3��m���1 cm���2), a good detection limit (of 101������10���9��m), excellent selectivity, and long-term stability. In vivo sensing tests on rabbits confirm a linear relationship between DA added to the animal eyes and the current response of the biosensor. Further tests on human tears sourced from defocus-induced myopia patients who have various myopia diopters show that the biosensor outputted a sensitive current signal that is related to the number of myopia diopters. This suggests there is an underlying relationship between myopia diopters and DA content in tears. It may provide a novel approach to a better understanding of myopia formation and its prevention.