Visudyne Photodynamic Therapy (PDT) is a specialized treatment designed for certain eye conditions that involve fluid leakage at the back of the eye. This two-stage procedure combines a light-activated drug called Visudyne with a specific non-thermal laser light. The primary goal of Visudyne PDT is to reduce the potential for central vision loss by targeting and sealing abnormal, leaking blood vessels behind the retina. This method offers a distinct approach compared to other laser treatments for eye disease, as it avoids burning the retina.
Understanding Photodynamic Therapy with Visudyne
Photodynamic Therapy (PDT) with Visudyne operates on the principle of using a photosensitizer drug, verteporfin (Visudyne), which is activated by a specific wavelength of light. Visudyne is transported in the bloodstream and is designed to accumulate in abnormal blood vessel cells. This allows the drug to concentrate in the target area, such as abnormal choroidal neovascularization (CNV).
Once the drug has circulated and localized in the abnormal vessels, a non-thermal red laser light, typically at a wavelength of 689 nm, is directed into the affected eye. This light activates the verteporfin, triggering a photochemical reaction. The activated drug generates highly reactive, short-lived singlet oxygen and other reactive oxygen radicals.
These reactive oxygen species cause localized damage to the endothelium, the inner lining of the abnormal blood vessels. This damage leads to a series of events, including platelet aggregation and the formation of fibrin clots, which ultimately result in the occlusion or sealing of the leaking vessels. This non-thermal process selectively treats the abnormal vessels while minimizing damage to surrounding healthy tissue.
Conditions Treated with Visudyne
Visudyne Photodynamic Therapy is primarily used for specific eye conditions characterized by the growth and leakage of abnormal blood vessels. The most common and FDA-approved indication for Visudyne is in the treatment of choroidal neovascularization (CNV) due to wet Age-related Macular Degeneration (AMD). Wet AMD involves the growth of new, fragile blood vessels under the macula, the central part of the retina responsible for sharp, detailed vision. These vessels can leak fluid and blood, leading to damage and potential rapid vision loss.
Visudyne therapy aims to reduce or delay vision loss associated with wet AMD by sealing these leaking vessels. While it does not typically reverse previous vision loss, it works to preserve existing vision. In addition to wet AMD, Visudyne PDT has received approval for treating CNV linked to pathologic myopia (severe nearsightedness) and presumed ocular histoplasmosis syndrome, which is a fungal eye infection. It has also been explored for other conditions like chronic central serous chorioretinopathy (CSCR), where fluid leaks behind the retina, though its use for certain other ocular conditions, like choroidal melanoma, is considered unproven.
The Visudyne Treatment Process
A Visudyne Photodynamic Therapy session typically follows a standardized two-step procedure, usually performed in an outpatient setting. The process begins with the administration of the Visudyne drug itself. The patient will have an intravenous (IV) line established, often in an arm vein, and the verteporfin solution is infused slowly over approximately 10 minutes.
Following the infusion, there is a waiting period of about 5 minutes to allow the drug to circulate throughout the body and accumulate in the abnormal blood vessels. Fifteen minutes after the start of the infusion, the second step, light activation, commences. The ophthalmologist will numb the eye with anesthetic eye drops and then place a special contact lens on the eye.
A non-thermal red laser light, with a recommended light dose of 50 J/cm² at an intensity of 600 mW/cm², is then directed through the contact lens onto the affected area of the retina. This laser application typically lasts for 83 seconds. During this time, the laser activates the Visudyne within the abnormal blood vessels, initiating the therapeutic effect without causing heat damage or pain.
After the Visudyne Procedure
Following a Visudyne Photodynamic Therapy procedure, patients must adhere to specific precautions due to temporary photosensitivity. For up to 5 days after receiving Visudyne, the skin and eyes will be highly sensitive to direct sunlight and very bright indoor lights. Exposure to intense light during this period can cause severe reactions, similar to a severe sunburn.
To mitigate this risk, patients are advised to wear protective clothing, such as long-sleeved shirts, pants, and wide-brimmed hats, along with dark sunglasses, when outdoors during daylight hours. Sunscreen creams do not offer protection against this type of photosensitivity. It is also important to avoid bright indoor lights, including tanning salons, bright halogen lighting, and the intense lights found in dental offices or surgical operating rooms.
Common temporary side effects can include injection site reactions, such as pain, redness, or swelling. Some patients may also experience visual disturbances like blurred vision or flashing lights, which usually resolve within hours. Less common side effects can include back pain during the infusion. Patients are encouraged to expose their skin to normal indoor light, as this helps to inactivate any remaining drug in the skin through a process called photobleaching.