Visual halos after sildenafil (Viagra): Author reply

Abstract

We are pleased to have the opportunity to clarify our results in light of recently published data by Behn et al. The curious increase in the values of the Naka-Rushton equation corresponding to Vmax and decrease in K, observed by Behn et al1Behn D Potter M.J Sildenafil-mediated reduction in retinal function in heterozygous mice lacking the γ-subunit of phosphodiesterase.Invest Ophthalmol Vis Sci. 2001; 42: 523-527PubMed Google Scholar in wild mice 1 hour after intraperitoneal injection of sildenafil, although not statistically significant, perfectly reproduces our data.We observed the same pattern in a group of 12 patients with a clinical diagnosis of erectile dysfunction 1 hour after oral ingestion of sildenafil, 50 mg (unpublished data). If the modifications of the intensity-response functions resemble the same pattern in all subjects and animals studied, it is highly improbable that they are carriers of a defective form of PDE6. It is noteworthy that full-field electroretinogram (ERG) studies obtained different responses: Vobig et al2Vobig A.M Klotz T Staak M et al.Retinal side-effects of sildenafil.Lancet. 1999; 353 ([letter]): 375Abstract Full Text Full Text PDF PubMed Scopus (94) Google Scholar reported a reduction in the a- and b-wave amplitudes; Kretschmann et al (Invest Ophthalmol Vis Sci 40, 1999) showed an increase in the dark adapted b-wave implicit time; more recently, Luu et al3Luu J.K Chappelow A.V McCulley T.J Marmor M.F Acute effects of sildenafil on the electroretinogram and multifocal electroretinogram.Am J Ophthalmol. 2001; 132: 388-394Abstract Full Text Full Text PDF PubMed Scopus (53) Google Scholar reported a small but significant delay in the a- and b-wave implicit times, a small increase in scotopic and photopic b-wave amplitudes in an ERG after ingestion of sildenafil, 100 mg and 200 mg.We advocate the use of intensity-response function to further investigate the effects of sildenfil on the retina, not only in relation to its higher sensitivity in respect to full-field ERG, but most importantly to better appreciate the exact role of cGMP inhibition on retinal function. We are pleased to have the opportunity to clarify our results in light of recently published data by Behn et al. The curious increase in the values of the Naka-Rushton equation corresponding to Vmax and decrease in K, observed by Behn et al1Behn D Potter M.J Sildenafil-mediated reduction in retinal function in heterozygous mice lacking the γ-subunit of phosphodiesterase.Invest Ophthalmol Vis Sci. 2001; 42: 523-527PubMed Google Scholar in wild mice 1 hour after intraperitoneal injection of sildenafil, although not statistically significant, perfectly reproduces our data. We observed the same pattern in a group of 12 patients with a clinical diagnosis of erectile dysfunction 1 hour after oral ingestion of sildenafil, 50 mg (unpublished data). If the modifications of the intensity-response functions resemble the same pattern in all subjects and animals studied, it is highly improbable that they are carriers of a defective form of PDE6. It is noteworthy that full-field electroretinogram (ERG) studies obtained different responses: Vobig et al2Vobig A.M Klotz T Staak M et al.Retinal side-effects of sildenafil.Lancet. 1999; 353 ([letter]): 375Abstract Full Text Full Text PDF PubMed Scopus (94) Google Scholar reported a reduction in the a- and b-wave amplitudes; Kretschmann et al (Invest Ophthalmol Vis Sci 40, 1999) showed an increase in the dark adapted b-wave implicit time; more recently, Luu et al3Luu J.K Chappelow A.V McCulley T.J Marmor M.F Acute effects of sildenafil on the electroretinogram and multifocal electroretinogram.Am J Ophthalmol. 2001; 132: 388-394Abstract Full Text Full Text PDF PubMed Scopus (53) Google Scholar reported a small but significant delay in the a- and b-wave implicit times, a small increase in scotopic and photopic b-wave amplitudes in an ERG after ingestion of sildenafil, 100 mg and 200 mg. We advocate the use of intensity-response function to further investigate the effects of sildenfil on the retina, not only in relation to its higher sensitivity in respect to full-field ERG, but most importantly to better appreciate the exact role of cGMP inhibition on retinal function.