N6-methyladenosine (m6A), the sixth N methylation of adenylate (A) in RNA, is the most abundant transcriptome modification in eukaryotic messenger RNA (mRNAs). m6A modification exists in both coding mRNA and noncoding RNAs, and its functions are controlled by methyltransferase, demethylase, and m6A reading proteins. Methylation modification of m6A can regulate RNA cleavage, transport, stability, and expression. This review summarizes the enzymes involved in RNA m6A methylation and the commonly used detection methods. The role of m6A modification in physiological processes is described, and its impact on tumorigenesis, viral infection, and diabetes is further highlighted. Moreover, up-to-date knowledge of the implications of RNA m6A modification in ocular diseases such as uveal melanoma and diabetic retinopathy is introduced. Clarifying the mechanism of RNA m6A methylation will help elucidate the pathogenesis of various diseases, providing options for subsequent treatment.