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Br J Ophthalmol 2006;90:927 doi:10.1136/bjo.2006.094375
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NAION and treatment of erectile dysfunction: reply from Pfizer

  1. R E Sobel1,
  2. J C Cappelleri2
  1. 1Pfizer Inc, Worldwide Development, 150 E 42nd Street, MS#150-3-72, New York, NY 10017, USA
  2. 2Pfizer Inc, Global Research and Development, Groton, CT, USA
  1. Correspondence to: Rachel E Sobel Pfizer Inc, Worldwide Development, 150 E 42nd Street, MS#150-3-72, New York, NY 10017, USA; rachel.sobel{at}pfizer.com
  • Accepted 9 March 2006

McGwin et al1 suggest that treatment of erectile dysfunction with sildenafil (Viagra) or tadalafil (Cialis), two phosphodiesterase inhibitors (PDE5-I), may increase the odds of non-arteritic anterior ischaemic optic neuropathy (NAION) in men with a history of myocardial infarction (MI) or hypertension (HTN). We believe, however, that this study is fraught with significant limitations (as the authors acknowledge) that preclude drawing any conclusions about this relation.

Case-control studies are susceptible to several biases that must be carefully considered and controlled for in the study design, implementation, and analysis.2 For example, accurate and complete ascertainment of exposure is critical in a …

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