Sir,

Wang et al1 should be commended for their effort to investigate the effects of phacoemulsification on the intraocular pressure (IOP) and ultrasound biomicroscopic image of filtering bleb in eyes with cataract and functioning filtering blebs. UBM is a good method used worldwide to observe the internal structure of filtering blebs.2 IOP is important for evaluating the filtering function of the eyes with filtering blebs. However, Wang et al claim that, unlike our results,3 the IOP increased after phacoemulsification at each follow-up visit.

In the discussion, Wang et al compared their results with the studies of Klink et al4 and Rebolleda et al.5 In all, 70.4% of the patients in Wang’s study were those with angle closure glaucoma compared with no patient in Klink’s study and only 6 of the 49 patients in Rebolleda’s study. Comparison of different types of glaucoma may make their study underpowered and of limited value.

We noticed in Wang’s study that the IOP before phacoemulsification ranged from 4.0 to 19.7 mm Hg. No patient required glaucoma medication. A 4 mm Hg IOP without antiglaucoma medicine was too low for most glaucoma patients. We wonder whether such patients have complications such as choroidal detachment, chronic hypotony or overfiltering bleb. Choroidal detachment may have its own natural evolutionary course, and hence after choroidal reattachment the IOP may increase. Phacoemulsification has been used to treat overfiltering blebs6 and chronic hypotony,7 and hence the IOP increase after phacoemulsification was not difficult to understand.

Visibility of the route under the scleral flap and reflectivity inside the bleb are two important aspects that can be help evaluate the UBM image of a filtering bleb. The authors claim that eyes with an invisible route under the scleral flap and stronger intrableb reflectivity in UBM image before phacoemulsification had greater postoperative antiglacuoma failure.

We believe that the status before phacoemulsification is indeed important, but the change occurring after phacoemulsification might be even more important because it may reflect the effect of the surgery. Our study showed that the increase in reflectivity inside the bleb after phacoemulsification might be a risk factor of IOP control failure.3 Unlike our study, Wang et al claim that the visible route under the scleral flap became invisible or narrower, and the low reflectivity inside the bleb increased in most eyes, but the changes before and after phacoemulsification did not have statistical significance. It would be of particular interest if the authors could do a further subgroup analysis to analyse why this happened.