Macular degeneration is a common eye condition that impacts central vision, which is responsible for tasks like reading and recognizing faces. This condition can significantly affect daily life as it progresses. Photodynamic therapy (PDT) is a treatment option used to address certain forms of macular degeneration. This article explores PDT, its application in macular degeneration, the treatment process, and expected outcomes.
Understanding Photodynamic Therapy
Photodynamic therapy (PDT) is a medical treatment that uses a light-sensitive drug, known as a photosensitizer, combined with a specific type of light to target diseased cells. In ophthalmology, the photosensitizer is verteporfin. This drug is administered intravenously and travels through the bloodstream.
Once verteporfin reaches the target area, a non-thermal laser light is applied. This light activates the drug, causing it to produce reactive oxygen species. These reactive oxygen species then act on the abnormal cells and blood vessels. This allows for selective targeting, closing off abnormal vessels without significantly damaging surrounding healthy retinal tissue.
The activation of verteporfin by the laser light leads to changes in local endothelial cells, the cells lining blood vessels. This triggers platelet binding and aggregation, resulting in the formation of clots and the occlusion of the abnormal blood vessels. This targeted action helps to prevent further leakage and damage to the retina.
Application in Macular Degeneration
Photodynamic therapy is specifically used for wet, or neovascular, age-related macular degeneration (AMD). In wet AMD, abnormal blood vessels, referred to as choroidal neovascularization (CNV), grow underneath the retina. These new vessels are fragile and often leak fluid and blood, which can lead to rapid and severe central vision loss.
The leakage from these abnormal blood vessels can cause the macula, the central part of the retina responsible for sharp, detailed vision, to swell or lift from its normal position. This fluid buildup distorts vision, causing straight lines to appear wavy or bent, and can result in dark spots in the central visual field. PDT selectively targets these leaky choroidal neovascularization membranes, helping to seal them off and prevent further fluid or blood from accumulating under the retina.
While anti-VEGF injections are now the primary treatment for wet AMD, PDT was historically important and continues to be used in certain cases. It can be effective for specific types of CNV lesions. PDT’s ability to directly occlude abnormal vessels makes it an effective treatment, sometimes used in combination with anti-VEGF therapies to improve patient results.
The Treatment Process and Recovery
The photodynamic therapy procedure begins with patient preparation. The eye to be treated is dilated to allow for better visualization during the procedure. Following dilation, the light-sensitive drug verteporfin is administered intravenously.
After the drug has circulated throughout the body for approximately 10 to 15 minutes, the non-thermal laser light is applied to the affected eye. The laser application lasts for about 83 seconds, targeting the abnormal blood vessels beneath the macula. Patients may experience a mild sensation during the laser application, though it is not painful.
Post-treatment care is important due to the photosensitizing nature of verteporfin. For at least 48 hours following the procedure, patients must avoid exposure to direct sunlight and bright indoor lights. This includes wearing dark sunglasses when outdoors and staying indoors as much as possible to prevent severe photosensitivity reactions, similar to a sunburn. Patients should also cover their skin with protective clothing if they must go outside.
Temporary visual disturbances, such as blurred vision or reduced sharpness, might occur immediately after the procedure, but these resolve. Mild discomfort, redness, or swelling in the treated eye are also possible and can be managed with cold compresses or over-the-counter pain relievers. It is also recommended to avoid hot tubs, saunas, and activities that cause excessive sweating for about a week.
Outcomes and Considerations
The primary goal of photodynamic therapy for wet AMD is to stabilize vision and prevent further loss, rather than to restore lost vision. PDT can reduce leakage from abnormal blood vessels and slow the progression of vision decline. While some patients may experience a reduction in leakage, the effects of PDT are often temporary, with abnormal vessels potentially reopening after about three months.
Many individuals require multiple treatments to achieve the full benefits, with the number of treatments varying based on individual response and the nature of the CNV. Follow-up examinations are regularly scheduled, often about a month after treatment, to monitor the eye’s response and determine the need for additional sessions.
Potential side effects include temporary visual disturbances, such as blurred vision or decreased vision, and reactions at the injection site like pain, swelling, or inflammation. A rare but serious side effect can be a severe, acute decrease in visual acuity within seven days of treatment, although vision may partially recover in some cases. Patient candidacy for PDT depends on factors like the type and location of choroidal neovascularization. PDT is frequently used in conjunction with anti-VEGF injections, as this combined approach can improve outcomes, reduce the number of required injections, and improve overall vision.