PDT for choroidal neovascularization
Hongge Wang
Photodynamic therapy (PDT), formerly known as photoradiotherapy and photochemotherapy, is a new technique that uses photodynamic reactions for disease diagnosis and treatment. Wang Hongge, Studio Ophthalmology
In 1995, a phase I/II clinical study of wet age-related macular degeneration (AMD) was conducted in the United States, in which most patients had improved visual acuity after PDT treatment, and fluorescence angiography results showed complete closure of choroidal neovascularization (CNV). Phase III clinical studies were conducted on this basis, and the follow-up results showed that PDT treatment not only prevented moderate to severe vision loss, but also improved vision, which provided a new treatment for choroidal neovascularization due to age-related macular degeneration, pathological myopia, and central exudative chorioretinopathy. 2000, the U.S. Food and Drug Administration (FDA) officially approved PDT for the clinical treatment of macular degeneration. China’s research in PDT started a little later than that in the United States and Japan, but progressed faster. At present, China has formed its own characteristics in photosensitizer development, related basic research and clinical application, and some fields have been in the forefront of the world.
Clinical characteristics of photodynamic therapy.
1. good tissue selectivity: PDT can act more specifically on target tissues and cells in the lighted area. This is the most outstanding advantage of photodynamic therapy, which can minimize the loss of function of vital organs and is especially suitable for high-precision treatment of vital organs. 2.
2. Superficial action: For most tissues, the effective depth of action of PDT is very shallow. Therefore, the main clinical indications for PDT are diseases in which the target tissue is a “thin” structure.
3. Strong damage effect on microvascular tissues: The endothelial cells of blood vessels are in direct contact with blood flow and have a large cell surface area, so they can absorb photosensitizers rapidly, and the photosensitizers and oxygen consumed in the photodynamic reaction can be replenished quickly. Therefore PDT is especially suitable for the treatment of microvascular diseases, such as wet age-related macular degeneration.
4. It is a local treatment method: the therapeutic effect of PDT is limited to the light range, so it is only suitable for diseases with limited lesion range.
5. Less systemic side effects: Since PDT is a local treatment method, there are no obvious systemic side effects, and it can be repeatedly used for many times. The destruction of lesion tissues triggered by photodynamic therapy is quite gentle in the course of action, and the physical and chemical stimulation of pain-sensitive nerves accompanying it is also very light.
The basic principle of photodynamic therapy: endogenous or exogenous photosensitive substances in biological tissues are exposed to corresponding wavelengths (visible light, near-infrared light or ultraviolet light), absorb photon energy and change from the ground state to the excited state, and the photosensitive substances in the excited state are very unstable and quickly return to the ground state after physical or chemical de-excitation process to release energy, and the physical de-excitation process can produce fluorescence, and through the analysis of fluorescence The physical de-excitation process can generate fluorescence, which can be used to diagnose diseases by analyzing the fluorescence spectrum; the chemical de-excitation process can generate a large amount of reactive oxygen species, which can interact with a variety of biological macromolecules to damage cell structures or affect cell functions, thus producing therapeutic effects. In the photodynamic effect system, physical and chemical degradation are two simultaneous and competing processes. The ability of photodynamic effects to be used in disease treatment is based on the ability of a particular lesion to take up and retain more photosensitizers while the target site is more susceptible to light irradiation. It is for this reason that the use of intense photodynamic effects to adequately destroy diseased tissue becomes a reality. In general, solid malignant tumors, some precancerous lesions and some benign lesions can take up and retain more photosensitizers, and as long as these lesions are within the reach of the laser fiber, they can be an indication for photodynamic therapy. Currently, the photosensitizing agents used for the treatment of non-neoplastic diseases are Visudyne (generic name verteporfin, or chemical structure abbreviated as BPD-MA) and 5-aminolaevulinic acid (ALA). Visudyne is commonly used clinically for the treatment of ophthalmic CNV.
Ophthalmic indications: For the treatment of typical predominant subcentral recess choroidal neovascularization due to age-related macular degeneration, pathological myopia, and central exudative chorioretinopathy. There is insufficient evidence to support Visudyne treatment in patients with occult subcentral sulcus choroidal neovascularization predominant.
Procedure: Dilate the patient’s pupils 30 minutes to 2 hours before infusion, dissolve Visudyne dry powder 15 mg in 7 ml of sterile water for injection (never dissolve the drug in a salt-containing solution), square the product of the patient’s height and weight and divide by 2 to determine the volume of diluted Visudyne used, then dilute to 30 ml with 5% GS, set the infusion time of the infusion pump at 10 minutes The infusion time of the infusion pump was set at 10 minutes, the rate at 3 ml/min, the infusion was started in a light-proof environment and a 15-minute countdown was started at the same time, local anesthesia was administered to the eye 2-5 minutes before the laser treatment, and the laser treatment was started at the end of the countdown. The laser wavelength is 689nm, light intensity 600mW/cm2, light dose 50J/cm2, irradiation time 83 seconds per eye, treatment area: lesion area diameter 1000um.
Caution: Some patients will feel back pain, headache, eye pain and nausea when injected, and the symptoms will gradually disappear at the end of the injection. The patient should wear dark glasses and stay at home for 5 days after the treatment to avoid direct sunlight and high-powered halogen lights. Patients mostly need two to three times of PDT to treat neovascularization.
Currently, it is more difficult to treat choroidal neovascularization due to various lesions. Recently, we have admitted many patients with wet age-related macular degeneration to our hospital. After PDT treatment, fundus examination, FFA and OCT examination have all seen significant improvement of macular lesions and visual acuity has been improved to different degrees, which fully indicates that photodynamic therapy has more positive efficacy in closing choroidal neovascularization.