Toxic retinopathiesSildenafil, Tamoxifen and Vigabatrin.(Features)

Sildenafil

Sildenafil citrate (Viagra) is an oral treatment for erectile dysfunction. It inhibits phosphodiesterase (PDE) Type 5, which degrades cyclic guanosine monophosphate (cGMP) in the corpus cavernosum of the penis. Increased levels of cGMP result in relaxation of smooth muscle within the corpus cavernosum and increased inflow of blood.

Symptoms and signs

Although Sildenafil is relatively selective for PDE Type 5, it has limited activity on PDE Type 6 - an enzyme involved in light excitation within the retina. Approximately 3 per cent of men taking the standard 50mg dose experience visual symptoms for up to several hours. These include a bluish tinge to the visual field, hypersensitivity to light, and, occasionally, blurred vision. Symptoms are more frequent with higher doses.

Numerous cases of non-arteritic ischaemic optic neuropathy (NAION) have been reported within 24 to 36 hours of sildenafil ingestion. As with NAION in general, men with cardiovascular co-morbities (for example, hypertension, diabetes, elevated cholesterol, or dyslipidaemia) may be at increased risk of this complication.

Management

Many patients are prepared to accept temporary alterations in their colour vision or light sensitivity. Previous episodes of NAION may be considered a relative contraindication.