Effect of sildenafil on ocular hemodynamics in 3 months regular use

Chronic sildenafil citrate use decreases retinal vascular endothelial growth factor expression in diabetic rats: a pilot study

BACKGROUND

Sildenafil citrate (SC) attenuates endothelial dysfunction. However, its effects on diabetic retinopathy (DR), which is mainly a microvascular disease, remain unclear. Vascular endothelial growth factor (VEGF) is known to be a critical mediator of DR. Therefore, we investigated the effects of SC on diabetic retina by measuring VEGF levels.

METHODS

In this study, twenty-eight rats were divided into the following groups: group I, the control group; group II, rats with streptozotocin-induced diabetes; group III, rats with streptozotocin-induced diabetes receiving daily oral sildenafil at 1 mg/kg; and group IV, rats with streptozotocin-induced diabetes receiving high-dose daily sildenafil at 2.5 mg/kg. After 3 months, VEGF was measured in the retina specimen in one eye and the vitreous body in the other eye by immunohistochemistry and enzyme-linked immunosorbent assay, respectively.

RESULTS

We found that VEGF expression in the retina was low in all rats from groups I and IV and in 30% of rats from group III; 80% of rats in group II demonstrated high VEGF expression in the retinae (P < 0.001). VEGF concentrations in the vitreous body samples were 32 ± 2, 61 ± 4, 44 ± 5, and 36 ± 3 pg/l in groups I-IV, respectively (P < 0.001).

CONCLUSION

VEGF decreased significantly in the eyes of diabetic rats after chronic oral sildenafil citrate treatment. SC may have a modifying/attenuating effect on DR. However, further studies are needed to evaluate its use as an adjunctive treatment.

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.

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.

Precautions and Monitoring of Patients Taking Phosphodiesterase Type 5 Inhibitors Who are at Risk of Increased Intraocular Pressure

Phosphodiesterase type 5 inhibitors (PDE5Is) may increase intraocular pressure (IOP) by increasing blood flow to the ciliary body. Although clinical studies of changes in IOP after single and multiple doses of PDE5Is show variable results, most are limited by small sample sizes, absence of control groups and blinding, and use of normal patient volunteers who have no risk factors for glaucoma. However, multiple case reports of glaucoma have been published, and one epidemiologic analysis of the National Health and Nutrition Examination Survey (NHANES) database of US respondents suggested a significant association of prolonged sildenafil use and self-reported glaucoma. With the widespread use of PDE5Is for treatment of erectile dysfunction in males with risk factors for glaucoma, and the potential of PDE5Is to worsen optic nerve damage in patients with glaucoma, we recommend a vision screening exam prior to the initiation of the PDE5I and careful follow-up thereafter, particularly if the patient is taking tadalafil, a long-acting PDE5I, if the patient is taking high doses of a PDE5I daily and persistently, and if the patient has risk factors for glaucoma or if the patient is at risk of worsening glaucoma.

Ocular Side Effects of Sildenafil That Persist Beyond 24 h-A Case Series

Acute secondary effects of sildenafil, a first-line pharmacotherapy for erectile dysfunction (ED), include headache, heartburn, skin flush, and vision changes. Generally, these effects subside within 5 h. This is a retrospective report of 17 cases in which patients experienced visual disturbances following 100-mg sildenafil use that persisted for more than 24 h. All 17 patients were healthy men taking sildenafil for the first time without prescriptions who sought consultation at our clinic within 48 h of taking the drug. Diagnostic tests indicated that out of the 17 patients, nine had photophobia, 13 had disrupted color perception, nine had impaired visual acuity, three had deficiencies in stereopsis, six had disrupted contrast sensitivity, and eight had abnormally dilated pupils. These disturbances resolved within 21 days in all 17 cases. There was near-full case overlap between photophobia and color vision impairment. In conclusion, because some individuals have heightened sensitivity to sildenafil, perhaps due to metabolic variance, patients should be started on a modest trial dose.

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 perfusion pressure and color Doppler imaging of the external ophthalmic artery of rabbits treated with sildenafil citrate

Background

It has been proposed that sildenafil citrate can increase ocular blood flow, and that this property can be used to treat ocular disorders that involve reflex vasoconstriction. This study therefore proposes to ascertain the vasodilator effect of the drug on retrobulbar circulation in healthy rabbits. For this matter rabbits treated with sildenafil citrate or saline solution had their intraocular pressure (IOP), mean arterial pressure (MAP), ocular perfusion pressure (OPP) and color Doppler imaging of the external ophthalmic artery measured prior to treatment and on days one (moment M1), seven (when M2), fourteen (moment M3), twenty-one (moment M4), and thirty (moment M5) of treatment.

Results

The MAP and OPP values of treated group were lower than those of control group at all times, and the mean values differed statistically at moments M1 (S = 71.52 mmHg, C = 84.76 mmHg, p = 0.0356) and M5 (S = 71.38 mmHg, C = 85.52 mmHg, p = 0.0252). The IOP and color Doppler values of the external ophthalmic artery did not differ between tested groups.

Conclusions

The dose of 10 mg of sildenafil citrate administered to healthy rabbits causes systemic vasodilation and consequently lower values of MAP and OPP. However, it does not induce changes in IOP and retrobulbar hemodynamics identifiable by color Doppler assessment of the external ophthalmic artery.

Regulation of intraocular pressure by soluble and membrane guanylate cyclases and their role in glaucoma

Glaucoma is a progressive optic neuropathy characterized by visual field defects that ultimately lead to irreversible blindness (Alward, 2000; Anderson et al., 2006). By the year 2020, an estimated 80 million people will have glaucoma, 11 million of which will be bilaterally blind. Primary open-angle glaucoma (POAG) is the most common type of glaucoma. Elevated intraocular pressure (IOP) is currently the only risk factor amenable to treatment. How IOP is regulated and can be modulated remains a topic of active investigation. Available therapies, mostly geared toward lowering IOP, offer incomplete protection, and POAG often goes undetected until irreparable damage has been done, highlighting the need for novel therapeutic approaches, drug targets, and biomarkers (Heijl et al., 2002; Quigley, 2011). In this review, the role of soluble (nitric oxide (NO)-activated) and membrane-bound, natriuretic peptide (NP)-activated guanylate cyclases that generate the secondary signaling molecule cyclic guanosine monophosphate (cGMP) in the regulation of IOP and in the pathophysiology of POAG will be discussed.

Sildenafil dilates ophthalmic artery in type 2 diabetic patients

Background:

Conflicting reports exist on the effect of sildenafil on ophthalmic artery blood flow; many visual disturbances due to vascular insult were reported with the use of sildenafil in diabetic patients like nonarteritic ischemic optic neuropathy.

Objectives:

The present work aimed to investigate whether sildenafil modulates ophthalmic artery vasoreactivity in patients with type 2 diabetes mellitus. Literature reports on this aspect are lacking.

Methods:

A total of 35 male subjects were enrolled in this study, 18 with type 2 diabetes mellitus matched with 17 normal individuals. Ophthalmic artery was insonated through a transorbital window using colored Doppler equipment with transcranial Doppler facility. Ophthalmic artery reactivity was assessed using breath holding/hyperventilation test, before and after giving 50 mg oral sildenafil.

Results:

It was found that in both normal subjects and diabetic patients, sildenafil increased baseline control of mean flow velocity of ophthalmic artery significantly (p < 0.05), breath holding caused a decrease of MFVopa (p < 0.05), and subsequent hyperventilation caused increase of MFVopa (p < 0.05). There was no statistically significant change in breath holding index and full range of vasodilatation of ophthalmic artery (p > 0.05) after sildenafil, in normal and diabetic groups. There was a significant increase of resistive index of ophthalmic artery flow in diabetic patients compared with that of normal subject (p < 0.05). Sildenafil decreased resistive index of ophthalmic artery flow significantly only in diabetic patients (p < 0.05).

Conclusion:

Sildenafil increased MFVopa, but had no significant effect on vasoreactivity of ophthalmic artery; sildenafil decreased resistive index only in type 2 diabetic patients.

Effect of sildenafil citrate on intraocular pressure and blood pressure in human volunteers

Anecdotal reports have suggested that the vasodilator, sildenafil citrate, which evokes its effect via a select inhibition of PDE5, has the potential to increase intraocular pressure (IOP) in some individuals. An ocular hypertensive effect by sildenafil was also recently described in a sheep animal model. In contrast, clinical studies have not found a direct association between sildenafil ingestion (commonly consumed as Viagra) and changes in IOP. However, some such studies also reported no effects of sildenafil on systemic blood pressure (BP) at the time of the IOP determination. Given this surprising result, our purpose was to repeat a study in human volunteers in the city of Corrientes, Argentina to corroborate the effects of sildenafil on human IOP and systemic BP. For the present study, 9 healthy volunteers (male and female, 18-74 years old) were selected as subjects after ophthalmic and cardiovascular evaluation indicated that they exhibited normal parameters for their age. In a masked, placebo-controlled study, the subjects ingested 100 mg sildenafil citrate (provided as Vorst from Laboratorios Bernabo, Argentina) in one session, and a placebo on a second separate occasion. IOP was measured with a Goldman applanation tonometer by an ophthalmologist, and BP by a second physician, neither of whom witnessed the tablet ingestion by the volunteers, nor provided with information on the nature of the test compounds. A third individual administered the tablets. The average baseline IOP of this group of 9 was 13.1 ± 0.6 mm Hg. Subsequent to sildenafil ingestion, IOP increased by 26% to 16.5 ± 0.8 mm Hg 60 min later (P < 0.005, as paired data), and returned to control values within 2 h. Both systolic and diastolic BP were significantly reduced by sildenafil ingestion. At the point of maximal systemic hypotension (90 min), the systolic and diastolic pressures declined by 15% and 13%, respectively. No significant changes in IOP or BP were recorded after ingestion of the placebo. Our results suggest that sildenafil can elicit a transient IOP increase that may be of importance to patients chronically treated with PDE5 inhibitors for various vascular diseases (e.g., pulmonary hypertension). We discuss possible mechanisms by which PDE5 inhibition might lead to a rise in IOP.

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.

Effects of Vardenafil on Intraocular Pressure and Orbital Hemodynamics

PURPOSE

The aim of this study was to investigate the effects of vardenafil on systemic blood pressure, intraocular pressure (IOP), and orbital hemodynamics.

METHODS

Twenty-one (21) volunteers suffering erectile dysfunction, with an average age of 51.5 +/- 6.2 years, were enrolled into the study. Brachial blood pressures and IOP were measured, the peak systolic velocity (PSV), end-diastolic velocity (EDV), and resistive index (RI) of the ophthalmic, central retinal, and posterior ciliary arteries were evaluated by color Doppler ultrasonography (CDU) before vardenafil intake. All measurements were repeated after 20 min of vardenafil intake. A paired Student t test was used to evaluate the changes.

RESULTS

Systolic blood pressure did not change significantly where diastolic blood pressure decreased significantly (P = 0.043) after drug ingestion. There was no significant change in IOP. Increase in EDV of CRA was significant (P = 0.04), but the increase of orbital blood flow velocities of OA and PCA were insignificant.

CONCLUSIONS

The recommended dose of vardenafil has no negative effects on orbital hemodynamics and IOP in patients with erectile dysfunction.