Objective:To observe the contribution of Borneolum syntheticum to the intervention effect of Liuwei Dihuang Pill(六味地黄丸,LDP) on experimental retinal degeneration,and initially investigate the mechanism of Borneolum syntheticum as meridian-lead-in drug.Methods:A total of 180 sodium iodateinduced retinital degeneration rats were randomly divided into three groups,including distilled water group,LDP group,and LDP+Borneolum syntheticum (LDP+BS) group.Twenty normal rats were fed regularly without any treatment as normal control.On day 7 and 14 after treatment,histopathological study and transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) test were performed to evaluate the retinopathy.Claudin-5 expression at blood-retina barrier (BRB) was detected by Western blot at different time points from 0.5 to 8 h after gavage.Results:On day 7 and 14 after treatment,the retinal lesion grades were significantly different among the three groups (P＜0.05).The grade in the LDP+BS group was significantly less than the LDP and distilled water groups (both P＜0.05),no significant difference was observed between the LDP and distilled water groups (P＞0.05).The apoptosis rates in the LDP+BS group was significantly less than the distilled water and LDP groups (both P＜0.05),while there was no significant difference between LDP and distilled water groups (P＞0.05).Expression of claudin-5 in LDP+BS group was significantly less than the other two groups at 0.5,1 and 2 h after gavage (P＜0.05).There was no apparent difference among the three groups at 4 and 8 h after gavage (P＞0.05).Conclusion:Borneolum syntheticum could strengthen the effect of LDP on experimental retinal degeneration,indicated that Borneolum syntheticum might play the role of meridian-lead-in drug in the formula.The mechanism may be due to Borneolum syntheticum could promote the physiologically openness of bloodretina barrier through transiently affecting the expression of claudin-5.