Given the growing body of evidence suggesting long-term intraocular pressure (IOP) fluctuation negatively affects visual parameters in patients with primary open-angle glaucoma (POAG) or primary angle-closure glaucoma (PACG), researchers recently set out to uncover which factors contribute to fluctuating pressure.

In a prospective study, they analyzed a total of 426 eyes from 269 patients, including 274 eyes with PACG and 152 eyes with primary angle closure (PAC) or PAC suspects (PACS). The study excluded eyes with laser or surgical IOP-lowering treatments, as these could significantly change the angle status or IOP within the two-year study period. Patients were followed every three months and evaluated with Goldmann applanation tonometry, as well as visual fields and SD-OCT imaging every six months.

Results of the multivariate analysis show higher baseline IOP, number of IOP-lowering medications, previous trabeculectomy, age, sex, diabetes and smoking are all significantly associated with IOP fluctuation over two years in primary angle-closure disease (PACD).

They also found other ocular characteristics such as the extent of peripheral anterior synechiae and central corneal thickness—commonly thought as significant risk factors for diurnal IOP fluctuation—were not associated with long-term IOP fluctuation in the study population. More research is necessary to better understand this finding, the study says.

Other associations of particular note include being on multiple IOP-lowering drugs at baseline and previous trabeculectomy. For the former, study authors speculate “the larger IOP fluctuation in these eyes may have resulted in a greater chance of additional IOP-lowering drugs being added on, and the additional drug(s) being continued, by doctors during clinic consultations.” As for previous trabeculectomy, which might appear contrary to previous findings, the results could be due to the study population and design. “Trabeculectomy is often reserved for relatively more advanced glaucoma eyes that have been on multiple IOP-lowering drugs for extended periods, because of the insufficient surgical operative capacity,” the authors say. In addition, “any filtration failure or decrease during the study period may be registered as long-term IOP fluctuation in a study of this design.”