Photodynamic Therapy

Photodynamic therapy (PDT) eliminates new vessels from the choroid (choroidal neovascularisation) without appreciable damage to the surrounding tissue.

It is a quick, minimally invasive procedure performed in an outpatient setting. It consists of the intravenous perfusion of a photosensitive drug, and its subsequent activation by a laser with a defined wavelength, verteporfin® (active substance used) that has an affinity for vascular endothelial cells in multiplication, i.e., where it is "accumulated" in the abnormal structures (neovessels) that are proliferating.

After 10 minutes of drug perfusion, a laser is emitted, with a wavelength of approximately 690 nm, which will act only on the previously identified structures.

Before treatment, some complementary diagnostic tests are carried out, such as fluorescein angiography, indocyanine green angiography and optical coherence tomography (OCT) of the posterior segment.

Photodynamic therapy is used in pathologies where there are abnormal vascular structures in proliferation. It was first used in cases of exudative age-related macular degeneration (AMD) with subfoveal choroidal neovascularisation, and in subfoveal choroidal neovascularisation secondary to pathological myopia.

More recently, its use has been shown to be effective in cases of central serous chorioretinopathy (macular oedema due to accumulation of fluid coming from the choroid) and in situations of subretinal neovascularisation (new blood vessels) below the fovea.

The treatment requires a prior preparation in which the patient's pupil is dilated and the eye is anaesthetised topically, i.e. with drops.

The dye is introduced during 10 minutes in a vein, drop by drop. 15 minutes after the end of the dye administration, the laser is applied for 83 seconds (time needed to activate the dye).

If treatment is required in both eyes, the light should be applied to the second eye immediately after the first, but no later than 20 minutes after the start of the infusion.

Prior to treatment, the patient's medical history should be analysed to see what medication they are taking and whether this may increase their sensitivity to light. Some medicines for bacterial infections, psychiatric illnesses, diabetes, high blood pressure, fungal infections, calcium channel blockers (used for high blood pressure, angina and abnormal heart rhythms), vasodilators and radiation therapy can have this effect. 

As this technique is non-invasive, the risks are minimal, and cases of allergy are rare. However, as verteporfin® is a photosensitive substance, after treatment, the patient is advised to avoid direct sunlight exposure during the first 48 hours, thus reducing the risk of burns, especially on the hands.

Photodynamic therapy should be used with caution in patients with moderate hepatic dysfunction or biliary obstruction. As verteporfin® is mainly eliminated via the biliary route and no studies are available for this group of patients. In patients with severe hepatic impairment, it is contraindicated.

After photodynamic therapy patients should be re-evaluated every 3 months, and in case of recurrent leakage, photodynamic therapy may be administered up to 4 times per year.

Patients who experience a severe decrease in visual acuity (equivalent to 4 lines or more) after treatment within one week, should not undergo retreatment, at least until their vision has fully recovered to pre-treatment levels, and until the potential benefits and risks of subsequent treatment have been carefully assessed by the treating physician.