We refer to the article by Tomsak1 on perspectives of PDE5 inhibitors (PDE5i) and permanent visual loss. Most statements in this paper are correct as separate observations, but the overall impression that (a) PDE5i increase the chances of developing nonarteritic anterior ischemic optic neuropathy (NAION) and (b) that patients prescribed PDE5i should be screened for ‘disc-at-risk’ do not follow from the separate statements.
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a)
Pfizer believes that, currently, there are no solid data to suggest a causal association between NAION and the use of PDE5i. Based on two large long-term observational studies2, 3 of approximately 32 000 men receiving a sildenafil prescription followed for more than 38 500 person-years of observation and more than 13 400 patients and 13 300 person-years of observation in 103 clinical trials with sildenafil for erectile dysfunction (ED), only one confirmed case of NAION has been identified, which is well within the estimated range of the annual incidence rate of NAION in the general adult population over the age of 50 years (i.e., 2.3–10 per 100 000 men per year). The author speculates how PDE5i could result in NAION and considers two possibilities: an effect on systemic blood pressure and a direct negative effect on optic nerve blood flow autoregulation. These are unlikely potential causative mechanisms for NAION secondary to sildenafil because effects of sildenafil on ocular circulation have been investigated in a number of clinical studies and all studies have shown either a neutral or even a positive effect on ocular blood flow, even when systemic blood pressure is lowered.4 A recent study looking at effects of sildenafil on ocular hemodynamics in men with ED following 3 months of regular use concluded that oral sildenafil had no effect on hemodynamic parameters.5
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b)
Although many ophthalmologists believe that a ‘disc-at-risk’ represents a risk factor for NAION, there is confusion around this concept. First, there is wide variability in the disc and cup sizes within the general population, such that there is no absolute cutoff between normal discs and ‘discs-at-risk’. Second, there are no good data on the prevalence of a ‘disc-at-risk’ in the general population or among men taking PDE5i. Third, it is not known for sure how a ‘disc-at-risk’ predisposes one to developing NAION since the actual pathophysiology is still unclear or how this might be affected by a PDE5i. Finally, if one accepts that the majority of people who have a ‘disc-at-risk’ never develop NAION (again, either with or without a PDE5i being involved), it is unclear what value screening for a ‘disc-at-risk’ would accomplish. In light of these facts, we are interested to know how the author would use screening information to make decisions about whether or not to prescribe a PDE5i.
Pfizer believes that, currently, there are no solid data to suggest a causal association between NAION and the use of PDE5i. Based on two large long-term observational studies2, 3 of approximately 32 000 men receiving a sildenafil prescription followed for more than 38 500 person-years of observation and more than 13 400 patients and 13 300 person-years of observation in 103 clinical trials with sildenafil for erectile dysfunction (ED), only one confirmed case of NAION has been identified, which is well within the estimated range of the annual incidence rate of NAION in the general adult population over the age of 50 years (i.e., 2.3–10 per 100 000 men per year). The author speculates how PDE5i could result in NAION and considers two possibilities: an effect on systemic blood pressure and a direct negative effect on optic nerve blood flow autoregulation. These are unlikely potential causative mechanisms for NAION secondary to sildenafil because effects of sildenafil on ocular circulation have been investigated in a number of clinical studies and all studies have shown either a neutral or even a positive effect on ocular blood flow, even when systemic blood pressure is lowered.4 A recent study looking at effects of sildenafil on ocular hemodynamics in men with ED following 3 months of regular use concluded that oral sildenafil had no effect on hemodynamic parameters.5
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