Objective  To investigate morphological change of uveoscleral outflow pathway after travoprost and pilocarpine are given alone or in combination.

  Methods  Of 28 normal albino rabbits, 4 were randomly selected as the control group (treated with normal saline for one day), and the remaining 24 rabbits were divided into three parallel groups and treated with 2% pilocarpine (3 times per day), 0.004%travoprost (per night), and their combination. On the 7th, 14th, and 24th day of the treatment, 2 rabbits in each drug-treated group were executed. Two rabbits in the control group were executed after treated with normal saline for one day. Eyeballs taken from these rabbits were fixed, and then the pathological specimens were prepared with hematoxylin-eosin (HE) staining and smooth muscle antibody (SMA) immunohistochemical staining. The morphological changes of ciliary smooth muscle and intracellular space were observed with optical microscope. Two normal rabbits from the control group were executed after normal saline treated for 1 day and 2 normal rabbits in each drug-treated group were executed after 24 days of treatment. All eyes of these rabbits were taken and emission electronic microscope specimens were made to observe the microstructure of ciliary muscle and extracellular matrix (ECM).

  Results  Specimens of pilocarpine group showed the contraction of ciliary muscle. Specimens of travoprost group showed the relaxation of ciliary muscle, enlargement of the extracellular space, and decompose of ECM. Specimens of the combination group showed the contraction of anterior 1/3 part of ciliary muscle but the relaxation of posterior 2/3 part of ciliary muscle. Decomposition of ECM was more distinct in combination group than those of individual groups.

  Conclusions  Compared with pilocarpine alone or travoprost alone, the combination of these two drugs does not increase the resistance of uveoscleral outflow pathway and probably can promote the aqueous fluid outflow by increasing the decomposition of ECM.