The present invention provides a single stranded nucleic acid molecule represented by the following formula (I):(I) (SEQ ID NO: 1) 5′-uagcaccauuugaaaucaguguucc-P- ggaacacugauuucaaauggugcuauu-3′ wherein —P— shows a proline derivative linker represented by the following formula (Ia):an agent for treating corneal diseases such as ocular surface disorders and the like, comprising the single stranded nucleic acid molecule as an active ingredient.