Objective To investigate the therapeutic effect of Vitamin A on the recovery of dry eye that was induced by benzalkonium chloride (BAC) topical medication in the mouse.Methods In this randomized controlled experimental study,50 BALB/c mice were treated with the topical administration of 0.25％ BAC to establish the dry eye condition.Based on the consistency of tear film break-up time (BUT),corneal fluorescein staining scores and inflammation index,the eyes were re-selected and 30 mice were randomly divided into three groups on day 21 after the BAC treatment,with 10 mice (20 eyes) in each group.Group C was set up as a blank control,while groups A and B were treated with 5000 IU/(g·ml) Vitamin A eye drops and microemulsion solvent drops,respectively.BUTs,corneal fluorescein staining scores,inflammation index and tear volumes were evaluated in each group on days 0,1,3,5 and 7 after the therapeutic treatment.Global specimens were collected on day 7.Sections were stained with hematoxylin and eosin (HE) or by periodic acid-Schiff (PAS) assay,and labeled with cytokeratin 10 (K10) antibody.The expression of K10 in the cornea and conjunctiva was quantified by Western Blot.The data were analyzed by one-way ANOVAs.Results On days 0,1,3 and 5,no clinical differences were observed among the groups.On day 7,the BUT values were (4.20±0.89)s,(3.32±1.01)s and (3.28±0.74)s in groups A,B and C,respectively.The BUT in group A was significantly longer than those in groups B and C (F=6.852,P=0.002).The corneal fluorescein staining scores were 3.74±1.31,5.47±1.81 and 5.83±1.54 in groups A,B and C,respectively.The scores in group A were significantly lower than those in groups B and C (F=8.853,P＜0.01).No significant differences were found in the corneal inflammatory index or tear volume among the groups.Corneal morphology showed a loosened corneal epithelium feature in groups B and C,but comeal integrity in group A.PAS assay revealed similar goblet cell numbers between group A and normal eyes,but fewer goblet cells in groups B and C.Cytokeratin 10 was almost negatively expressed in Vitamin A treated groups,while it remained positive in the entire corneal epithelial layer with other treatments.The level of K10 in the cornea was down-regulated in Vitamin A treated groups.Conclusion Vitamin A treatment presented marked therapeutic effects on BAC-induced mouse dry eye,with a more stable tear film,better recovery of epithelial integrity,an increased number of goblet cells,and the elimination of squamous metaplasia,when compared to the treatment of microemulsion solvent eye drops only or without treatment.This experiment show the great potential of Vitamin A in the clinical treatment of dry eye.