Is Viagra (sildenafil) safe to use in patients with keratoconus?

Viagra (Sildenafil) Safety in Patients with Keratoconus

Viagra (sildenafil) is generally safe to use in patients with keratoconus, as there is no evidence suggesting that it worsens corneal ectasia or affects corneal biomechanics. While sildenafil can cause mild, transient visual effects, these are not specifically contraindicated in keratoconus patients.

Mechanism of Action and Visual Effects

Sildenafil works by:

• Selectively inhibiting cGMP-specific phosphodiesterase type 5 (PDE5) in vascular tissue
• Exerting minor inhibitory action against PDE6, which is present in rod and cone photoreceptors 1

These effects can cause:

• Transient visual symptoms (blue tinge to vision, increased brightness of lights)
• Mild impairment of color discrimination around peak plasma levels
• Slight delays in photopic and 30-Hz flicker electroretinogram responses
• Minor attenuation of multifocal electroretinogram waveforms across the posterior pole 2

Safety Profile in Relation to Keratoconus

Keratoconus is characterized by:

• Progressive corneal thinning and cone-like steepening
• Irregular astigmatism and reduced vision
• Complex etiology involving genetic, environmental, biomechanical, and cellular factors 3

Important considerations:

1. No Direct Interaction: The 2024 Corneal Ectasia Preferred Practice Pattern guidelines do not list PDE5 inhibitors as medications that affect keratoconus or contraindicate their use 4.

2. Retinal vs. Corneal Effects: Sildenafil's visual effects primarily involve retinal function rather than corneal structure or biomechanics. The medication affects photoreceptors through PDE6 inhibition, not corneal collagen or keratocytes 1.

3. Temporary Effects: Studies show that visual effects from sildenafil are transient and mild, with parameters remaining within normal limits even at high doses (200mg) 2.

4. Long-term Safety: No long-term visual system effects have been observed in extensive clinical use of sildenafil, with over 15 million men prescribed the medication 1.

Clinical Recommendations

When considering sildenafil use in keratoconus patients:

• Monitor Visual Symptoms: Patients should be informed about possible transient visual effects (blue tinge, increased brightness).

• Avoid in Advanced Disease: Exercise caution in patients with advanced keratoconus who already have significantly compromised vision, as any additional visual disturbance might be more problematic.

• Consider Timing: If possible, advise patients to take sildenafil at times when optimal vision is less critical (e.g., evening rather than before driving).

• Regular Follow-up: Maintain regular ophthalmologic follow-up for keratoconus progression as normally indicated, regardless of sildenafil use.

Management of Keratoconus

The primary focus for keratoconus patients should remain on:

• Avoiding eye rubbing, which is the only modifiable risk factor for progression 5
• Appropriate vision correction (glasses, contact lenses)
• Corneal cross-linking (CXL) for progressive disease 4
• Surgical interventions for advanced cases when indicated

Conclusion

While sildenafil can cause mild, transient visual effects, there is no evidence that it adversely affects corneal structure or accelerates keratoconus progression. The medication's effects on the visual system are well-characterized, temporary, and primarily retinal rather than corneal in nature.