A substance having the following formula is provided. Wherein R1 and R2 are selected from a group consisting of &agr; -Ara, &bgr; -Ara and &bgr; -Xyl. The substance has an effect of accelerating a phagocytosis of RPE.本發明提供一種具有如式一結構的物質, 式一;其中R1與R2分別選自α-阿拉伯糖(α-Ara)、β-阿拉伯糖(β-Ara)以及β-木糖(β-Xyl)其中之一。