A method of treating a retinal disease that leads to photoreceptor loss or outer-retina degeneration, includes administering a compound of formula (Ia) or a pharmaceutically acceptable salt thereof to a patient having the retinal disease so as to be delivered to an eye of the patient in an amount effective to treat the retinal disease:wherein A is an 5-oxazolyl residue or a pyridine-4-yl residue, R1 is selected from the group consisting of methoxy, fluoro and chloro； R2, R3, R4, R5 and R6 of the phenyl ring B are independently from each other selected from the group consisting of hydrogen, a linear or branched alkyl having 1 to 4 carbon atoms, trifluoromethyl, 2,2,2-trifluoroethyl, methylsulfanyl, ethylsulfanyl, methylsulfonyl, ethylsulfonyl, difluoromethoxy, trifluoromethoxy, fluoro, bromo, chloro, methoxy, ethoxy, propoxy, butoxy, hydroxy and amino； and at least two of R2, R3, R4, R5 and R6 are hydrogens.
