A double-blind placebo-controlled evaluation of the acute effects of sildenafil citrate (Viagra) on visual function in subjects with early-stage age-related macular degeneration

Association of sildenafil use with age-related macular degeneration: a retrospective cohort study

OBJECTIVE

Despite significant advances in clinical care and understanding of the underlying pathophysiology, age-related macular degeneration (AMD)-a major cause of global blindness-lacks effective treatment to prevent the irreversible degeneration of photoreceptors leading to central vision loss. Limited studies suggest phosphodiesterase type 5 (PDE5) inhibitors, such as sildenafil, may prevent AMD by increasing retinal blood flow. This study explores the potential association between sildenafil use and AMD risk in men with erectile dysfunction using UK data.

METHODS AND ANALYSIS

Using the UK's IQVIA Medical Research Data, the study analysed 31 575 men prescribed sildenafil for erectile dysfunction and no AMD history from 2007 to 2015, matched with a comparator group of 62 155 non-sildenafil users in a 1:2 ratio, over a median follow-up of approximately three years.

RESULTS

The primary outcome was the incidence of AMD in the two groups. The study found no significant difference in AMD incidence between the sildenafil users and the non-users, with an adjusted hazard ratio (HR) of 0.99 (95% CI 0.84 to 1.16), after accounting for confounders such as age, ethnicity, Townsend deprivation quintile, body mass index category, and diagnosis of hypertension and type 2 diabetes.

CONCLUSION

The study results indicated no significant association between sildenafil use and AMD prevention in UK men with erectile dysfunction, suggesting sildenafil's protective effect on AMD is likely insignificant.

The Impact of Systemic Medications on Retinal Function

This study will provide a thorough review of systemic (and select intravitreal) medications, along with illicit drugs that are capable of causing various patterns of retinal toxicity. The diagnosis is established by taking a thorough medication and drug history, and then by pattern recognition of the clinical retinal changes and multimodal imaging features. Examples of all of these types of toxicity will be thoroughly reviewed, including agents that cause retinal pigment epithelial disruption (hydroxychloroquine, thioridazine, pentosan polysulfate sodium, dideoxyinosine), retinal vascular occlusion (quinine, oral contraceptives), cystoid macular edema/retinal edema (nicotinic acid, sulfa-containing medications, taxels, glitazones), crystalline deposition (tamoxifen, canthaxanthin, methoxyflurane), uveitis, miscellaneous, and subjective visual symptoms (digoxin, sildenafil). The impact of newer chemotherapeutics and immunotherapeutics (tyrosine kinase inhibitor, mitogen-activated protein kinase kinase, checkpoint, anaplastic lymphoma kinase, extracellular signal-regulated kinase inhibitors, and others), will also be thoroughly reviewed. The mechanism of action will be explored in detail when known. When applicable, preventive measures will be discussed, and treatment will be reviewed. Illicit drugs (cannabinoids, cocaine, heroin, methamphetamine, alkyl nitrite), will also be reviewed in terms of the potential impact on retinal function.

Long-term follow-up of retinal morphology and physiology after 2000 mg sildenafil overdose as a means of attempted suicide: a case report

Background

Few case reports have described sildenafil overdose, particularly ingestion of > 1000 mg, and overdose-induced changes in visual function remain unclear. We report retinal morphology, retinal sensitivity, and findings of electrophysiological evaluation over long-term follow-up in a case of sildenafil overdose (2000 mg).

Case presentation

Our patient developed visual abnormalities in the paracentral visual field accompanied by photophobia, decreased contrast sensitivity, and difficulty distinguishing colors in both eyes, 8 hours after the sildenafil overdose. These symptoms did not improve throughout the course, and although abnormalities of retinal morphology and sensitivity, as well as the electroretinogram findings showed slight improvement, the patient did not recover completely at 6-month follow-up.

Conclusions

We observed that high-dose sildenafil ingestion leads to retinal toxicity; the ocular abnormalities may persist for at least 6 months. Optical coherence tomography, Humphrey perimetry, microperimetry, and multifocal electroretinography are useful to quantitatively monitor temporal changes.

Sildenafil in ophthalmology: An update

Sildenafil citrate, a selective oral phosphodiesterase 5 inhibitor, is a widely used drug for erectile dysfunction that acts by elevating cGMP levels and causing smooth muscle relaxation. It also has 10% activity against PDE6, a key enzyme in phototransduction cascade in the retina. Recent ocular imaging developments have further revealed the influence of sildenafil on ocular hemodynamics, particularly choroidal perfusion. Choroidal thickness is increased, and choroidal perfusion is also enhanced by autoregulatory mechanisms that are further dependent on age and microvascular abnormalities. Studies demonstrating high intraocular pressure via a "parallel pathway" from increased choroidal volume and blood flow to the ciliary body have challenged previous concepts. Another new observation is the effect of sildenafil on bipolar cells and cyclic-nucleotide gated channels. We discuss potential deleterious effects (central serous chorioretinopathy, glaucoma, ischemic optic neuropathy, and risks to recessive carriers of retinitis pigmentosa), potential beneficial effects (ameliorate choroidal ischemia, prevent thickening of Bruch membrane, and promote recovery of the ellipsoid zone) in macular degeneration, as well as potential drug interactions of sildenafil.

Development of Phosphodiesterase-Protein-Kinase Complexes as Novel Targets for Discovery of Inhibitors with Enhanced Specificity

Phosphodiesterases (PDEs) hydrolyze cyclic nucleotides to modulate multiple signaling events in cells. PDEs are recognized to actively associate with cyclic nucleotide receptors (protein kinases, PKs) in larger macromolecular assemblies referred to as signalosomes. Complexation of PDEs with PKs generates an expanded active site that enhances PDE activity. This facilitates signalosome-associated PDEs to preferentially catalyze active hydrolysis of cyclic nucleotides bound to PKs and aid in signal termination. PDEs are important drug targets, and current strategies for inhibitor discovery are based entirely on targeting conserved PDE catalytic domains. This often results in inhibitors with cross-reactivity amongst closely related PDEs and attendant unwanted side effects. Here, our approach targeted PDE–PK complexes as they would occur in signalosomes, thereby offering greater specificity. Our developed fluorescence polarization assay was adapted to identify inhibitors that block cyclic nucleotide pockets in PDE–PK complexes in one mode and disrupt protein-protein interactions between PDEs and PKs in a second mode. We tested this approach with three different systems—cAMP-specific PDE8–PKAR, cGMP-specific PDE5–PKG, and dual-specificity RegA–R_D complexes—and ranked inhibitors according to their inhibition potency. Targeting PDE–PK complexes offers biochemical tools for describing the exquisite specificity of cyclic nucleotide signaling networks in cells.

Visual Side Effects Linked to Sildenafil Consumption: An Update

Phosphodiesterase type 5 (PDE5) inhibitors such as Viagra^® (sildenafil citrate) have demonstrated efficacy in the treatment of erectile dysfunction (ED) by inducing cyclic guanosine monophosphate (cGMP) elevation followed by vasodilation and increased blood flow. It also exerts minor inhibitory action against PDE6, which is present exclusively in rod and cone photoreceptors. The effects of sildenafil on the visual system have been investigated in a wide variety of clinical and preclinical studies due to the fact that a high dose of sildenafil may cause mild and transient visual symptoms in some patients. A literature review was performed using PubMed, Cochrane Library and Clinical Trials databases from 1990 up to 2020, focusing on the pathophysiology of visual disorders induced by sildenafil. The aim of this review was not only to gather and summarize the information available on sildenafil clinical trials (CTs), but also to spot subpopulations with increased risk of developing undesirable visual side effects. This PDE inhibitor has been associated with transient and reversible ocular side effects, including changes in color vision and light perception, blurred vision, photophobia, conjunctival hyperemia and keratitis, and alterations in the electroretinogram (ERG). Sildenafil may induce a reversible increase in intraocular pressure (IOP) and a few case reports suggest it is involved in the development of nonarteritic ischemic optic neuropathy (NAION). Reversible idiopathic serous macular detachment, central serous retinopathy and ERG disturbances have been related to the significant impact of sildenafil on retinal perfusion. So far, sildenafil does not seem to cause permanent toxic effects on chorioretinal tissue and photoreceptors as long as the therapeutic dose is not exceeded and is taken under a physician’s direction to treat a medical condition. However, the recreational use of sildenafil can lead to harmful side effects, including vision changes.

Effects of phosphodiesterase type 5 inhibitors on choroid and ocular vasculature: a literature review

To provide information on the effects of phosphodiesterase type 5 (PDE5) inhibitors on choroidal vessels and central serous chorioretinopathy (CSC) and possible implications for development of exudative age-related macular degeneration (AMD). Two independent investigators conducted a qualitative review of PubMed to identify studies on the choroidal effect of PDE5 inhibitors in June 2019. The search used key words that included PDE5 inhibitors, sildenafil, tadalafil, vardenafil, choroid, choroidal flow, choroidal vessels, choroidal thickness, CSC, AMD or a combination. Only studies which assessed choroidal findings were included. Many ocular diseases are related to changes in choroidal thickness and perfusion. Patients with AMD, who have decreased choroidal perfusion, may manifest more severely diminished choroidal ability to deliver oxygen and other metabolites to the retina, leading to growth of neovascular tissue. As a result of this engorgement of the choroidal vasculature, some patients may have leakage across the retinal pigment epithelium (RPE) and accumulation of subretinal fluid, resulting in CSC. Transient visual symptoms, i.e., changes in color perception and increased light sensitivity, are well-known adverse effects, but there have been rare reports of vision-threatening ocular complications in users of PDE5 inhibitors, such as nonarteritic anterior ischemic optic neuropathy and cilioretinal artery occlusion. The choroid is a vascular tissue analogous in many respects to the corpus cavernosum, and PDE5 inhibitors may increase the choroidal thickness and perfusion. While it is intuitively obvious that thickness of the choroid alone does not guarantee better choriocapillaris oxygenation, it is a reasonable step towards ameliorating ischemia. These drugs have numerous physiologic effects on the choroid related to blood flow, such as clinical consequences in CSC and AMD.

Ocular side effects of Levitra® (vardenafil) - results of a double-blind crossover study in healthy male subjects

Purpose

To determine ocular side effects of vardenafil with special regard to color vision and retinal function.

Methods

This was a single center, randomized, double-blind, placebo-controlled, twofold crossover study with an administration of a single oral dose of two 20 mg tablets of BAY 38–9456 (vardenafil hydrochloride) or corresponding placebo in 24 healthy male subjects. Ocular investigations included Farnsworth–Munsell D100 color vision test, electroretinogram, and basic ophthalmological examinations like visual acuity, visual field, and slit-lamp of anterior segment and fundus.

Results

Compared to placebo, administration of vardenafil hydrochloride lead to a temporary significant increase of Farnsworth–Munsell D100 total error score after 1 and 6 hours as well as in error lines 3 and 4 after 1 hour. Twenty-four hours after administration there was no significant alteration of total error score or of any error line. While latency of electroretinogram b-wave remained unaffected, amplitudes showed a significant decrease compared to placebo 1 hour following administration. While other ocular examinations did not reveal any differences in general some mild to moderate but no serious adverse events have been reported.

Conclusion

Despite temporary changes in retinal function our study reports good tolerability of vardenafil in regard to ocular side effects.

Pathophysiology of visual disorders induced by phosphodiesterase inhibitors in the treatment of erectile dysfunction

Aim

The aim of this review was to summarize the ocular action of the most common phosphodiesterase (PDE) inhibitors used for the treatment of erectile dysfunction and the subsequent visual disorders.

Method

This is a literature review of several important articles focusing on the pathophysiology of visual disorders induced by PDE inhibitors.

Results

PDE inhibitors have been associated with ocular side effects, including changes in color vision and light perception, blurred vision, transient alterations in electroretinogram (ERG), conjunctival hyperemia, ocular pain, and photophobia. Sildenafil and tadalafil may induce reversible increase in intraocular pressure and be involved in the development of non-arteritic ischemic optic neuropathy. Reversible idiopathic serous macular detachment, central serous chorioretinopathy, and ERG disturbances have been related to the significant impact of sildenafil and tadalafil on retinal perfusion.

Discussion

So far, PDE inhibitors do not seem to cause permanent toxic effects on chorioretinal tissue and photoreceptors. However, physicians should write down any visual symptom observed during PDE treatment and refer the patients to ophthalmologists.

Complement pathway biomarkers and age-related macular degeneration

In the age-related macular degeneration (AMD) 'inflammation model', local inflammation plus complement activation contributes to the pathogenesis and progression of the disease. Multiple genetic associations have now been established correlating the risk of development or progression of AMD. Stratifying patients by their AMD genetic profile may facilitate future AMD therapeutic trials resulting in meaningful clinical trial end points with smaller sample sizes and study duration.

Update on current and future novel therapies for dry age-related macular degeneration

Age-related macular degeneration (ARMD) is the leading cause of irreversible blindness in developed countries. There are currently no cures, but there are promising potential therapies that target the underlying disease mechanisms of dry ARMD. Stem cells, ciliary neurotrophic factor, rheopheresis, ozonated autohemotherapy and prostaglandins show promise in stabilizing or improving visual acuity. Age-Related Eye Disease Study vitamins may reduce progression to severe ARMD. Adjuvant therapy like low vision rehabilitation and implantable miniature telescopes may help patients adjust to the sequelae of their disease, and herbal supplementation with saffron, zinc monocysteine and phototrop may be helpful. Therapies that are currently in clinical trials include brimonidine, doxycycline, anti-amyloid antibodies (GSK933776 and RN6G), RPE65 inhibitor (ACU-4429), complement inhibitors (ARC1905, FCFD4514S), hydroxychloroquine, intravitreal fluocinolone acetate and vasodilators like sildenafil, moxaverine and MC-1101. Therapies that have not been shown to be effective include POT-4, eculizumab, tandospirone, anecortave acetate, the antioxidant OT-551, sirolimus and vitamin E.

Phosphodiesterase inhibitors and the eye

Phosphodiesterase type 5 (PDE5) inhibitors are effective oral treatments for erectile dysfunction and have become one of the most widely prescribed medications worldwide. The mechanism of action is to reduce the degradation of cyclic GMP (cGMP) potentiating the effect of nitric oxide in the corpus cavernosum and allowing erectile function to occur by consequent relaxation of penile smooth muscle. Because of the presence of PDE5 in choroidal and retinal vessels these medications increase choroidal blood flow and cause vasodilation of the retinal vasculature. The most common symptoms are a blue tinge to vision and an increased sensitivity to light. There have been reports of non-arteritic anterior ischaemic optic neuropathy and serous macular detachment in users of PDE5 inhibitors, although a causal relationship has not been conclusively shown. Despite the role of cGMP in the production and drainage of aqueous humour these medications do not appear to alter intraocular pressure and are safe in patients with glaucoma. All PDE5 inhibitors weakly inhibit PDE6 located in rod and cone photoreceptors resulting in mild and transient visual symptoms that correlate with plasma concentrations. Psychophysical tests reveal no effect on visual acuity, visual fields or contrast sensitivity; however, some studies show a mild and reversible impairment of blue-green colour discrimination. PDE5 inhibitors transiently alter retinal function on electroretinogram testing but do not appear to be retinotoxic. Despite the role of cyclic nucleotides in tear production there is no detrimental effect on tear film quality. Based on the available evidence PDE5 inhibitors have a good ocular safety profile.

Ocular Safety in Patients Using Sildenafil Citrate Therapy for Erectile Dysfunction

Sildenafil citrate improves erectile function in men with erectile dysfunction (ED) by selectively inhibiting cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5), which is present in all vascular tissue. Sildenafil also has a weaker inhibitory action on PDE6, located in the rod and cone photoreceptors. Modest, transient visual symptoms, typically blue tinge to vision, increased brightness of lights, and blurry vision, have been reported with sildenafil use and occur more frequently at higher doses. Visual function studies in healthy subjects and in patients with eye disease suggest that sildenafil does not affect visual acuity, visual fields, and contrast sensitivity. Transient, mild impairment of color discrimination can occur around the time of peak plasma levels. Spontaneous postmarketing reports of visual adverse events, including nonarteritic anterior ischemic optic neuropathy (NAION), have been reported during the 7 years that sildenafil has been prescribed to more than 27 million men worldwide. However, because men with ED frequently have vascular risk factors that may also put them at increased risk for NAION, a causal relationship is difficult to establish. No consistent pattern has emerged to suggest any long-term effect of sildenafil on the retina or other structures of the eye or on the ocular circulation.

Visual side effects associated with erectile dysfunction agents

PURPOSE

To describe the known ocular side effects of agents used to treat erectile dysfunction.

DESIGN

Retrospective observational case series and literature review.

METHODS

We reviewed 892 case reports from the National Registry of Drug-Induced Ocular Side Effects (Casey Eye Institute, Portland, Oregon), the Food and Drug Administration (FDA), and the World Health Organization (WHO) and conducted a comprehensive review of the literature.

RESULTS

Ocular side effects of these drugs appear fully reversible and transitory.

CONCLUSIONS

To date, evidence does not exist to discourage use of erectile dysfunction agents attributable to harmful ocular side effects. Ischemic optic neuropathy (ION) is "possible" by WHO classification, however, conclusive evidence linking ION to erectile dysfunction medications is still lacking.

Effect of Viagra on the foveolar choroidal circulation of AMD patients

To investigate the effects of sildenafil citrate (Viagra) on foveolar choroidal circulation in patients with age related macular degeneration (AMD). Double-blinded, randomized, placebo-controlled, crossover study. Fifteen male AMD patients received a dose of 100 mg of sildenafil or matching placebo on two separate days. Laser Doppler flowmetry was performed to assess relative choroidal blood velocity (ChB(Vel)), volume (ChB(Vol)) and flow (ChB(Flow)) in the study eye prior to administration of the drug at baseline and 30, 90, 180, 300 min after dosing. Best corrected visual acuity (BCVA), contrast sensitivity (CS), mean arterial blood pressure (BPm), heart rate (HR), intraocular pressure (IOP) and ocular perfusion pressure (PP) were determined. In comparison to placebo, sildenafil did not cause any statistically significant changes in mean ChB(Vel) (ANOVA, P=0.12), ChB(Vol) (ANOVA, P=0.24) or ChB(Flow) (ANOVA, P=0.46). There were no statistically significant changes in CS (ANOVA, P=0.59), BCVA (P=0.58), IOP (P=0.81) or HR (P=0.07) throughout the study. Significant decreases in BPm (P=0.006) and PP (P=0.006) were observed at 30 min after sildenafil. Administration of sildenafil citrate didn't cause any statistically significant changes in the foveolar choroidal circulation of AMD patients.

Effects of sildenafil on blue-on-yellow and white-on-white Humphrey perimetry in 3 months regular use

PURPOSE

To assess the effects of sildenafil on blue-on-yellow (B/Y) and white-on-white (W/W) Humphrey perimetry in a group of men with erectile dysfunction in 3 months regular use.

METHODS

In this prospective study, 14 patients with erectile dysfunction received 50 mg doses of sildenafil (Viagra, Pfizer) two times per week regularly for 3 months. Patients underwent best-corrected visual acuity (BCVA), colour vision, anterior segment and fundus examination, and B/Y and W/W Humphrey perimetry in each eye before and after sildenafil treatment. Changes in mean deviations (MD) were compared separately for both eyes.

RESULTS

No significant changes from baseline were observed in BCVA and colour vision after sildenafil treatment. The anterior segment and fundus examinations revealed no abnormalities. There was no change on B/Y and W/W Humphrey visual field. MD values of B/Y and W/W Humphrey perimetry remained nonsignificant for both eyes after 3 months regular use of sildenafil (P=0.133, and 0.092, respectively, for right, and P=0.221 and 0.925, respectively, for left eyes).

CONCLUSION

Oral sildenafil used regularly for 3 months produced no effect on B/Y and W/W Humphrey perimetry.

The effects of sildenafil on ocular blood flow

PURPOSE

To investigate the effects of sildenafil, a popular new drug in the treatment of erectile dysfunction, on ocular blood flow.

METHODS

This study was designed as a prospective, double-blind, placebo-controlled study. Twenty participants with erectile dysfunction were given a single oral dose of 100 mg sildenafil, while 10 participants with erectile dysfunction were given placebo. All the participants underwent routine systemic and ophthalmological examinations. Intraocular pressure, systolic and diastolic blood pressure and ocular blood flow (ophthalmic, central retinal, short posterior ciliary arteries) were measured in both eyes before and 1 hour after the dose of sildenafil or placebo. Ocular blood flow measurements were performed using colour Doppler ultrasonography.

RESULTS

None of the parameters were significantly different between the groups before study drug intake. Although central retinal artery velocities were not changed, ophthalmic artery and short posterior ciliary artery peak systolic velocity, end-diastolic velocity, and mean velocity values were significantly increased 1 hour after drug intake in the sildenafil group compared to the placebo group (p < 0.05).

CONCLUSION

Sildenafil causes a significant increase in blood flow in these arteries. A possible role of inhibition of phosphodiesterase-5 in vascular smooth muscles by sildenafil is implicated. Further studies are needed to investigate the effects of sildenafil on ocular blood flow in patients with senile macular degeneration, diabetic retinopathy and glaucoma.

Visual short-term effects of Viagra: double-blind study in healthy young subjects

PURPOSE

To investigate short-term visual effects of a single 100-mg dose of Viagra (sildenafil citrate) in healthy men.

DESIGN

Randomized, double-blind, placebo-controlled clinical trial of drug effects on normal volunteers conducted by a single center.

METHODS

Twenty men, aged 20 to 40 years, were treated with either a placebo or 100 mg sildenafil. Visual function tests included electroretinogram (ERG) recordings, on-/off- and 3.3 Hz-flicker-ERG recordings, anomaloscope matches, and measurements of cone contrast sensitivities and transient tritanopia.

RESULTS

Most visual tests did not differ between the sildenafil and placebo groups. However, statistically significant increases in sensitivity during transient tritanopia were observed as well as significant prolongations in the implicit times of scotopic a-wave, photopic b-wave, and 3.3 Hz-flicker a-wave and b-wave ERG recordings. The magnitude of the differences correlated with peak sidenafil plasma concentration. Although rod amplitudes of the ERG recordings tended to be higher and cone amplitudes lower in the sildenafil group after drug ingestion, the differences were nonsignificant. There were no reports of visual side effects, and all electrophysiologic and psychophysical measurements returned to the normal range within 24 hours.

CONCLUSIONS

A single oral dose of 100-mg sildenafil given to healthy young men led to small but statistically significant transient changes of outer and inner retinal function, as detected by ERG and psychophysical methods. Although the acute effects were fully reversible within 24 hours, it would be worthwhile to compare them with those induced by other PDE5 and PDE6 inhibitors.

Viagra (sildenafil citrate) and ophthalmology

Viagra (sildenafil citrate) improves penile erections in men with erectile dysfunction (ED) by selectively inhibiting cGMP-specific phosphodiesterase type 5 (PDE5), which is present in all vascular tissue. It also exerts a minor inhibitory action against PDE6, which is present exclusively in rod and cone photoreceptors. At higher doses, sildenafil causes mild and transient visual symptoms in a minority of patients (mainly blue tinge to vision, increased brightness of lights). Therefore, the effects of sildenafil on the visual system have been investigated in a wide variety of clinical and preclinical studies. In preclinical studies, sildenafil shows transient reversible effects on electrical response to light. In long-term toxicology studies in which animals were exposed to high multiples of the maximum human therapeutic dose, detailed examinations have revealed no adverse effects on the structure or function of the eye. The effects of sildenafil have been systematically investigated in visual function studies in volunteers and in patients with eye disease; sildenafil does not affect visual acuity, visual fields, and contrast sensitivity. The only definite effect is transient, mild impairment of color discrimination occurring around the time of peak plasma levels. In long-term studies, no long-term effects of sildenafil on the visual system have been observed. Postmarketing, sildenafil has been prescribed to over 15 million men with ED. Isolated examples of a variety of visual adverse events have been reported. No consistent pattern has emerged to suggest any long-term effect of sildenafil on the retina or other structures of the eye. Based on this experience, intermittent, short-term, partial inhibition of PDE5 or PDE6 by sildenafil is unlikely to induce any long-term visual change.

A 4-year update on the safety of sildenafil citrate (Viagra)

Clinical studies have demonstrated that sildenafil citrate (Viagra) is an effective and well-tolerated oral treatment for erectile dysfunction. Despite its established safety profile, concern about its cardiovascular safety persists among some physicians and the general public. This concern has stemmed primarily from sporadic reports of adverse events published in the literature and sensationalized by the media. However, the only absolute contraindication for sildenafil is concurrent use of nitrates. Because sildenafil has been on the market for 4 years and under clinical investigation for even longer, we can now evaluate its long-term safety in men who have been taking the drug for several years. We review this issue from 3 perspectives. First, we reassess the overall safety profile of sildenafil by reviewing the initial controlled clinical trials and open-label studies. We present new data from patients who have been exposed to sildenafil for up to 4.5 years. We also evaluate the results from independent postmarketing studies. Second, we review the cardiovascular-specific results from the clinical trials, long-term extension, and postmarketing studies. Lastly, we review the specific effects on the visual system based on findings from studies conducted during drug development and post marketing.