Effects of sildenafil on ocular perfusion demonstrated by color Doppler ultrasonography

Histopathology and electron microscopy evaluation of the sildenafil effect on diabetic rats' retinae

PURPOSE

Although there is increasing evidence that phosphodiesterase-5 (PDE-5) inhibitors modify the effect of diabetes on different tissues, its effect on diabetic retinopathy is not well studied.

METHODS

Forty male Sprague-Dawley (SD) rats were divided into four groups: group I = control group that received no treatment; group II (diabetic group), in which diabetes was induced by a single streptozotocin injection; group III (sildenafil small dose, SSD), in which diabetes was similarly introduced (however, rats received daily oral 1 mg/kg sildenafil citrate (SC) for 3 months); and group IV (sildenafil large dose, SLD), which was as in group 3, but SC was 2.5 mg/kg. After 3 months, globes were removed and retinae were dissected; one globe from each rat was examined by light microscopy (LM), and the other by electron microscopy (EM).

RESULTS

In contrast to the control group, diabetic rats in group II demonstrated well-established diabetic changes in the form of capillary congestion, decreased cell population, hyaline changes of capillary walls, and degenerated nerve fiber layer by LM. Similarly, EM demonstrated photoreceptor degeneration, mitochondrial cristolysis, and vacuolated depleted cells among other features in group II. These diabetic features were less prominent in group III and nearly absent in group IV.

CONCLUSION

SC use in the early stages of DR may prevent/delay diabetic retinopathy development or progression in diabetic rat models, an effect that seems to be dose-related.

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.

Evaluation of Retinal and Choroidal Microcirculation Alterations After a Single Dose of Oral 5-mg Tadalafil: A Prospective Pilot Optical Coherence Tomography Angiography Study

Purpose: To evaluate the effects of a single dose of oral 5-mg tadalafil on macular microcirculation as measured using optical coherence tomography (OCT) and angiography (OCTA) in healthy volunteers. Methods: Twenty-two healthy, middle-aged, sexually active, and male health care worker volunteers were included in this prospective study. All volunteers have a history of occasionally using off-label 5 mg tadalafil to enhance sexual performance. Superficial and deep capillary plexus vascular densities, foveal avascular zone parameters, outer retina, and choriocapillaris flow areas were performed using the OCTA, and subfoveal-choroidal thickness (CT) was performed by using the OCT. Measurements were performed preintake, 30 min, 1, 4, 24 h, 2, 3, 4, and 7 days after the intake of tadalafil off-label. Results: Twenty-two eyes of 22 male volunteers were included in the study. The mean age was 37.16 ± 4.52 years. At 30 min, 1 h, and 4 h after intake, a statistically significant increase was observed in the choriocapillaris flow area and CT compared with preintake (Friedman test, P = 0.034 and P < 0.001, respectively). Conclusion: This study showed that a single dose of oral 5-mg tadalafil causes an increase in choriocapillaris flow and CT. To evaluate the effects of tadalafil on the retina and choroid, an OCTA assessment may be helpful.

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.

Treatment of Macular Degeneration with Sildenafil: Results of a Two-Year Trial

OBJECTIVE

To evaluate PDE5/6 inhibition with sildenafil to reduce choroidal ischemia and treat age-related macular degeneration.

METHODS

Sildenafil was prescribed to treat participants with macular degenerations or macular dystrophies measured by spectral-domain optical coherence tomography, color fundus photography, enhanced depth imaging, and best-corrected visual acuity.

RESULTS

No change in calcified drusen was noted. Vitelliform-type soft drusen were not substantially changed. A participant with Best vitelliform macular dystrophy had a significant improvement in vision as well as in photoreceptor and ellipsoid layers.

CONCLUSIONS

Our research supports sildenafil as a safe treatment for age-related and vitelliform macular degenerations. Thickened Bruch's membrane reduces the beneficial effect of perfusion increase, but all eyes appear to benefit from PDE6. Notably, maintenance or improvement in the photoreceptor layer may be the most significant result of sildenafil and is consistent with PDE6 inhibition. Thus, sil-denafil treatment of macular degeneration offers significant potential for vision retention and recovery.

Changes in Retinal and Choroidal Vascular Blood Flow after Oral Sildenafil: An Optical Coherence Tomography Angiography Study

Purpose

To describe changes in the retina and choroidal flow by optical coherence tomography angiography (OCT-A) after a single dose of oral sildenafil.

Method

A case-control study. Patients in the study group received 50 mg of oral sildenafil. Patients in the control group received a sham pill. Retinal and choroidal images were obtained at baseline (before pill ingestion) and 1 hour after ingestion. Central macular and choroidal thickness, choroidal and outer retina flow, and the retinal and choroidal vascular density were compared using a Mann-Whitney U test.

Results

Twenty eyes were enrolled into the study group and 10 eyes in the control group. There was a significant difference in central choroidal thickness and outer retina blood flow between groups after 1 hour of sildenafil ingestion (p < 0.01). There were no differences in central macular thickness, choroidal flow, and retinal vascular density among groups.

Conclusions

A single dose of oral sildenafil increases choroidal thickness, probably due to sildenafil-induced vasodilation.

Use of phosphodiesterase inhibitors and prevalence of self-reported glaucoma in the United States

Objective

While decreased ocular blood flow is thought to be a possible contributor to glaucoma pathogenesis, it is unclear what role systemic phosphodiesterase inhibitors (PDEi) play. We performed a cross-sectional study of a nationally representative sample of the U.S. population to investigate the relationship between the most commonly used PDEi, sildenafil and theophylline, and self-reported glaucoma.

Methods

We used the National Health and Nutrition Examination Survey 2005–2008 cycles for this observational study. 7,042 participants, aged 40 years and over, responded to a survey item on glaucoma status and were included in the analysis. Multivariable logistic regression models were constructed to evaluate the association between at least 1 year of self-reported PDEi use and prevalent glaucoma. Regressions were adjusted for potential confounding variables, including demographics, socioeconomic status, and general health conditions, and accounted for the complex design of the survey. Sample weights were constructed and used to ensure the generalizability of results.

Results

482 respondents self-reported a diagnosis of glaucoma, of which 11 used sildenafil and 20 used theophylline for at least 1 year. Covariates significantly associated with higher odds of glaucoma prevalence in univariable analyses included older age, black race, former smoking status, diabetes, hyperlipidemia, myocardial infarction, and stroke. Conversely, higher education and income were significantly associated with lower odds of glaucoma prevalence. In regression analyses adjusted for demographic and socioeconomic variables, sildenafil (OR = 4.90, CI: 1.24–19.27, p = 0.025) and theophylline (OR = 3.15, CI: 1.46–6.80, p = 0.005) were significantly associated with higher odds of self-reported glaucoma. These associations held after further adjustment with general health behaviors and conditions for both sildenafil and theophylline.

Conclusions

Use of sildenafil and theophylline for one or more years was associated with greater prevalence of self-reported glaucoma, a finding which requires further prospective study to assess causality and possible mechanisms of action.

Erectile Dysfunction Agents and Nonarteritic Anterior Ischemic Optic Neuropathy

Phosphodiesterase-5 inhibitors (PDE5I) are used for treatment of erectile dysfunction and pulmonary arterial hypertension and have been implicated as a causative factor for development of nonarteritic anterior ischemic optic neuropathy (NAION). Controversy remains regarding a cause and effect between PDE5I use and NAION because the mechanism by which NAION occurs is still not well understood. Because neuro-ophthalmologists have accepted that there is a potential relationship between ingestion of the PDE5I class of medications and NAION, the neuro-ophthalmologist should inquire about PDE5I use when evaluating a patient with a new diagnosis of NAION, and counsel patients regarding the implication of continued use of PDE5I.

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.

Ocular toxicity assessment of chronic sildenafil therapy for pulmonary arterial hypertension

PURPOSE

The aim of this study was to investigate possible functional and structural ocular changes caused by chronic sildenafil therapy to treat pulmonary arterial hypertension (PAH).

METHODS

Case-control study included patients with pulmonary arterial hypertension: chronically using sildenafil and without sildenafil treatment. A comprehensive ophthalmologic exam including ectoscopy, extrinsic ocular motility, logMAR visual acuity measurement, contrast sensitivity test, color test, anterior segment biomicroscopy, Schirmer test 1, intraocular pressure, fundus exam under pupil dilation, fundus pictures, time domain and spectral domain optical coherence tomography, ocular Doppler ultrasound were performed. Full-field electroretinography (ERG) was tested for each eye in a subgroup of sildenafil-treated patients.

RESULTS

Twenty patients from each group were tested. Bilateral severe keratitis was found in seven (35 %) patients under sildenafil therapy. Lacrimal film break-up time (BUT) was significantly reduced (p = 0.006 respectively) and Doppler ultrasound showed a reduced resistance index of the central retinal artery in the group of sildenafil users (p = 0.019). No diffuse retinal functional abnormalities were found in ERG in treated patients. Visual acuity, contrast sensitivity and color discrimination were normal in both groups. No abnormalities were found in both time-domain and spectral-domain OCT for retinal parameters.

CONCLUSIONS

One-third of the treated PAH group showed severe bilateral keratitis. This finding could be related to connective tissue abnormalities usually present in patients with this condition that might be exacerbated with the sildenafil usage. The resistance index of the central retinal artery was diminished in the chronic users group and it could be associated to the vasodilation caused by the medication in the choroidal vessels. An ophthalmic assessment for these patients is recommended to diagnose and treat possible ocular surface and choroidal blood flow abnormalities caused by sildenafil.

Contrast sensitivity, ocular blood flow and their potential role in assessing ischaemic retinal disease

PURPOSE

To examine the definition, evaluation methodology, association to ocular blood flow and potential clinical value of contrast sensitivity (CS) testing in clinical and research settings, focusing in patients with ischemic retinal disease.

METHODS

A review of the medical literature focusing on CS and ocular blood flow in ischemic retinal disease.

RESULTS

CS may be more sensitive than other methods at detecting subtle defects or improvements in primarily central retinal ganglion cell function early on in a disease process. CS testing attempts to provide spatial detection differences which are not directly assessed with standard visual acuity chart testing. Analyzing all studies that have assessed both CS change and ocular blood flow, it is apparent that both choroidal circulation and retinal circulation may have an important role in influencing CS.

CONCLUSION

The concept that CS is directly influenced by ocular blood flow is supported by reviewing the studies involving both. Although the studies in the literature have not established a direct cause and effect relationship per se, the literature review makes it logical to assume that changes in retinal and choroidal blood flow influence CS. This raises the possibility that a subjective visual characteristic, specifically CS, may be able to be evaluated more objectively by studying blood flow. It appears appropriate to study the relationship between blood flow and CS more extensively to develop improved ways of measuring various aspects of blood flow to the eye and to best quantify early changes in visual function.

The effects of sildenafil citrate on choroidal thickness as determined by enhanced depth imaging optical coherence tomography

PURPOSE

To investigate the effects of the phosphodiesterase-5 inhibitor, sildenafil citrate, on choroidal thickness using eye-tracked enhanced depth imaging spectral-domain optical coherence tomography.

METHODS

In a prospective interventional study, 8 healthy subjects (4 men and 4 women) with no ocular history underwent enhanced depth imaging spectral-domain optical coherence tomography at baseline, 1 hour, and 3 hours after the ingestion of 100 mg of sildenafil citrate. Choroidal thickness measurements for both eyes using enhanced depth imaging spectral-domain optical coherence tomography were taken by 2 masked readers at baseline, 1-hour, and 3-hour time points. Statistical analysis was performed to compare the measurements of choroidal thickness at each of the three intervals.

RESULTS

The mean age of the subjects was 35.9 years (range 30-46 years). Mean choroidal thickness at baseline was 334 μm (± 57 μm). Mean choroidal thickness increased by 12.3% to 375 μm (± 68 μm) at 1 hour after ingestion (P < 0.001). At 3 hours after ingestion, the mean choroidal thickness remained elevated at 372 μm (± 61 μm), 11.6% thicker than baseline (P < 0.001). There was no significant difference in choroidal thickness between the 1-hour and the 3-hour intervals (P = 0.719).

CONCLUSION

Sildenafil citrate appears to increase choroidal thickness as measured by eye-tracked enhanced depth imaging spectral-domain optical coherence tomography measurements in healthy subjects 1 hour and 3 hours after ingestion. These findings may be of relevance given that increased choroidal thickness appears to be a risk factor for central serous chorioretinopathy and that several reports have suggested an association between phosphodiesterase-5 inhibitors and this disorder.

Anterior ischemic optic neuropathy and stroke with use of PDE-5 inhibitors for erectile dysfunction: cause or coincidence?

The PDE-5 inhibitors sildenafil (Viagra) vardenafil (Levitra) and tadalafil (Cialis) have been taken by millions of men for erectile dysfunction. Transient visual symptoms are common but there also have been fourteen cases of nonarteritic anterior ischemic optic neuropathy (NAION) described in patients using these drugs as well as a few other vascular events. NAION is a common optic neuropathy in patients in the age group using these drugs and the question arises whether or not PDE-5 inhibitors are causing NAION. One case of NAION occurred after transient visual symptoms occurred with repeated use and one patient experienced a transient ischemic attack after taking a dose followed by a stroke on using the drug again later. Other than these two cases with strong dechallenge-rechallenge data, the evidence to support PDE-5 inhibitors as a cause of NAION or any vascular event is weak. PDE-5 inhibitors probably are a rare cause of a common ischemic disorder of the optic disc. They should be avoided in men who have already experienced NAION in one eye. Patients should be warned to seek medical attention if they have visual field or acuity loss after using PDE-5 inhibitors. Otherwise there is little basis for modifying the current guidelines for the use of these drugs.

Expression of the PDE5 enzyme on human retinal tissue: new aspects of PDE5 inhibitors ocular side effects

OBJECTIVE

We tested the effect of two phosphodiesterase type-5 (PDE5) inhibitors, sildenafil and tadalafil, on ophthalmic artery (OA) blood flow velocity and investigated the presence of the PDE5 enzyme on human retinal tissue in comparison with the PDE6 enzyme localization.

METHODS

Using Colour Doppler ultrasonography (CDU) we investigated, in 30 healthy young subjects (27.8 years of age; range, 24.3-33.7 years), the effects of a single oral dose of sildenafil (100 mg), tadalafil (20 mg), and placebo on OA blood flow velocity. Western blot for PDE6 and PDE5 protein expression was performed on frozen samples of human retina, testis, sperm, skin, and corpus cavernosum. Immunohistochemistry was performed on two ocular globes from dead donors.

RESULTS

CDU showed a relationship between the administration of PDE5 inhibitors and OA blood flow velocity modifications in a time-dependent manner. Western blot and immunohistochemical analysis showed PDE6 and PDE5 presence in human retinal tissue and gave a map of its distribution.

CONCLUSION

We demonstrated that (a) tadalafil and sildenafil are able to modify the OA flux in a time-dependent manner; (b) the PDE5 enzyme is expressed on retinal and choroid vasculature (smooth muscle and endothelial cells), on ganglion and bipolar cells; (c) human retinal tissues express the PDE6 enzyme in the rod and cone photoreceptors; (d) visual side effects after PDE5 inhibitors administration may be linked to a specific effect on the PDE5 enzyme; and (e) the PDE5 enzyme may have a physiologic role on ganglion and bipolar cells that need to be further investigated.

Optic atrophy after sildenafil use

BACKGROUND

It has been well-reported that phosphodiesterase-5 (PDE-5) inhibitors, originally investigated for their effect on smooth muscles and now used widely in treatment of erectile dysfunction, can cause mild transient visual disturbances because of their action on inhibiting enzymes involved in retinal transduction. Recently, these medications have been associated with the development of non-arteritic anterior ischemic optic neuropathy (NAAION) with attendant vision loss.

CASE REPORT

An older male patient, previously examined and ocularly healthy, presented asymptomatically with an occult optic neuropathy, not characteristic of NAAION. Neuroimaging and serology failed to reveal any other underlying cause. The patient did, however, report the use of sildenafil during the interval between his previously normal examination and the observation of his optic neuropathy.

CONCLUSIONS

This case details the development of an optic neuropathy with atrophy seemingly associated with the use of sildenafil, although no cause and effect could be conclusively found. This may indicate that medications used in the treatment of erectile dysfunction may be responsible for optic neuropathies other than NAAION.

Effect of sildenafil on ocular hemodynamics in 3 months regular use

The aim of this study was to evaluate the effect of sildenafil on ocular hemodynamics in a group of men with erectile dysfunction in 3 months regular use. A total of 15 patients with erectile dysfunction were included in this prospective study. All patients received 50 mg doses of sildenafil (Viagra, Pfizer) two times per week regularly for 3 months. The following examinations were performed on both eyes before and after sildenafil treatment: best-corrected visual acuity (BCVA), intraocular pressure (IOP), color vision, anterior segment, and fundus examination. Using color Doppler imaging, we measured hemodynamic variables in the ophthalmic artery (OA), central retinal artery (CRA), and short posterior ciliary artery (SPCA). No significant changes in BCVA, color vision and IOP were found after sildenafil treatment. The anterior segment and fundus examinations showed no abnormalities. All Doppler parameters of OA, CRA, and SPCA remained nonsignificant for both eyes after sildenafil treatment. Oral sildenafil in 3 months regular use seems to have no effect on ocular hemodynamics.

Effects of Sildenafil Citrate (Viagra®) on Renal Arteries: An Evaluation with Doppler Ultrasound

INTRODUCTION

We aimed to determine hemodynamic alterations in renal arteries that may have resulted from oral intake of sildenafil citrate in healthy volunteers.

MATERIALS AND METHODS

Twelve healthy volunteers were included in our study. Renal Doppler ultrasonography (US) was performed before the drug intake to assess the basal values. Maximum peak systolic velocity, and resistivity and pulsatility indices were measured from the segmental branches of both renal arteries in all the examinations. After the basal measurements 50 mg of sildenafil or placebo were randomly given to the 12 subjects. Renal Doppler US examinations were carried out 1 h after sildenafil or placebo intake. On the following day sildenafil was administered to the subjects who had previously taken placebo or vice versa. Renal Doppler US was repeated after 1 h. The effect of sildenafil on renal vascular hemodynamics was evaluated by comparison of basal values with postplacebo and postsildenafil values.

RESULTS

No statistically significant differences were found between the basal values of bilateral renal arteries and maximum peak systolic velocity, and resistivity and pulsatility index values measured after the placebo or sildenafil intake.

CONCLUSION

We demonstrated that single-dose sildenafil did not cause any significant effect on renal artery hemodynamics in healthy individuals.

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.