We read, with great interest, the paper by Topouzis and associates. The authors should be congratulated for their work, because population-based studies are needed to provide accurate information about the prevalence of any disease in the general population. In this sense, the conclusions the authors reach about the prevalence of pseudoexfoliation (PEX), pseudoexfoliative glaucoma (PEXG), and primary open-angle glaucoma (POAG) in the Greek population are sound. Nevertheless, Topouzis and associates also analyze the influence of IOP in the development of glaucoma. For this kind of analysis, it is mandatory to evaluate the untreated IOP of the population studied. In fact, this is what the authors do, but as the prevalence of both PEXG and POAG in the general population is relatively low, and because some of their patients were already under therapy, the number of untreated PEXG eyes they analyzed was low (17 eyes).
Despite this evident limitation, they found a significant difference in the untreated IOP levels between PEXG and POAG. They found that PEX has higher association with glaucoma (compared to no PEX) for the same untreated IOP level, but this association was found only for IOP level > 20 mm Hg. The authors also state in their paper that “there is only 1 previous report in which a direct comparison between newly diagnosed POAG and PEXG was performed.” This statement is not correct, in my mind, for 2 main reasons. First, Futa and associates study patients at their first visit to the clinic, but some of them were already under medical treatment (timolol and/or pilocarpine), so conclusions about the untreated IOP cannot be obtained from this paper. Second, there is a paper (we published years ago) specifically designed to evaluate the untreated IOP in PEXG and POAG. Our study evaluated the correlation between the untreated IOP and the visual field defect in both POAG (31 eyes) and PEXG (31 eyes). Interestingly, we obtained similar results to Topouzis and associates; ie, PEXG eyes seem to have an increased vulnerability to high IOP, compared to POAG eyes. We found that in newly diagnosed PEXG, the higher the untreated IOP level at diagnosis, the higher the mean defect (MD) of the visual field, with a quite high correlation coefficient between both parameters (r = 0.68). On the contrary, we found no significant correlation between IOP and MD in POAG.
The conclusion is that in PEXG the main risk factor that explains almost all of the visual field damage is IOP, and that PEX eyes seem to have a quite homogeneous optic nerve vulnerability to increased IOP. On the other hand, POAG eyes seem to show a quite heterogeneous vulnerability to IOP; although the risk to develop POAG increases with high IOP levels, this increase in risk is much lower than in PEXG. A possible explanation could be that in POAG, risk factors other than IOP, such as genetic predisposition, vascular factors, etc, may play a significant role in glaucoma development.