Photodynamic Therapy - Ocular Usage

Introduction

Photodynamic therapy involves the combination of a light source and light-sensitive medicine to kill abnormal cells. It is used in the treatment of body parts where the light source can reach, such as skin, mouth, lungs, esophagus, eye conditions, and certain types of cancer as well. The light and the light source are harmless on their own. This therapy eliminates the need for surgery.

What Are the Types of Photodynamic Therapy?

There are two ways to use photodynamic therapy. They are

• Conventional Photodynamic Therapy - In this, a light source can be a lamp or laser.

• Natural Photodynamic Therapy - The light source used here is daylight.

How Is the Procedure Done?

Conventional PDT:

1. Preparation:

• To start with the treatment, the individual must get a medical opinion and the prescribed drug. The given drug is in the form of a cream, injection, or a special drink containing a photosensitizing agent.

• A photosensitizing agent is a material that activates in response to a particular kind of light. Porfimer sodium, aminolevulinic acid (ALA), and methyl aminolevulinate (MAL) are common photosensitizing agents that are used in the treatment.

• After taking the medicine, the subject should wait for a few hours to two days. By that time, the medicine gets absorbed by the abnormal cells.

2. Light Treatment:

• The light source in conventional treatment involves the light source from the lamp or laser.

• The light is shown on the treatment area for about 10 to 45 minutes.

• Local general anesthetics can be given to numb the area of the treatment.

• Reactive oxygen species are produced when the photosensitizer is activated by light.

• Cell death or the obliteration of aberrant tissue are possible outcomes of this damage. PDT's choice allows for the accurate selection of specific cells while minimizing damage to adjacent healthy tissue.

Daylight PDT:

Preparation is the same as the conventional method, only the light source is different in daylight PDT.

Light Treatment:

• After taking the medicine, stay outdoors in the sunlight for around two days.

• Sunlight activates the medicine.

• Apply sunscreen before undergoing the therapy.

After the treatment, the area is covered with a dressing. Try to avoid scratching and keep the area dry. It takes about two to four weeks to heal.

Which Ocular Condition Is Treated by PDT?

Age-related macular degeneration (AMD) is one of the conditions for which photodynamic therapy (PDT) is used in ophthalmology, especially when the condition is associated with the "wet" or neovascular form of the illness. Following that, neovascular AMD, also known as "wet" AMD, is treated with a photosensitive agent that is activated by a laser. Neovascular AMD is a condition whereby abnormal blood vessels grow underneath the layers of the retina and leak fluid or blood. This could lead to the development of vision-impairing choroidal neovascularization (CNV). A photosensitizing agent, such as verteporfin, is injected into the patient's bloodstream. The material accumulates in the unusual blood vessels that are present in the eyes. After that, a laser is used to activate the photosensitizer, which seals the abnormal blood vessels without significantly damaging the surrounding healthy tissue.

Other Eye Problems Include:

• Central serous retinopathy.

• Polypoidal choroidal vasculopathy.

• Choroidal hemangiomas

• Capillary hemangiomas.

Procedure:

• The drug is injected into the bloodstream and waits for 10 minutes. This helps to take the medicine.

• Then, the ophthalmologist fixed the contact lens in the eyes to be treated.

• The laser, which seals off the blood vessels and causes leakage, is shown.

What Could Be the Effect of PDT Contact Lenses?

• A tear in the corneal epithelium paves the way for germs to get in, causing infection of the stroma.

• The epithelium of a normal cornea is made up of a smooth layer with tightly connected plasma membranes.

• Studies have shown the release of epidermal growth factor from hydrogel contact lenses in defective corneal epithelium.

What to Expect After the Eye Surgery?

• The vision would be blurry, and it would last for one day.

• Avoid exposing the eye to sunlight because the medicine is light-sensitive.

• Wear sunglasses and a wide hat to avoid sunlight.

• Getting the treatment done only minimizes the risk of losing vision.

• Vision gets better in conditions like Astigmatism, corneal disease, refractive errors, etc.

When Is PDT Contraindicated?

Though the process is safe, it should not be used in:

• Porphyria: PDT is usually not recommended for people who have porphyria, a rare genetic disorder involving the skin and nervous system.

• Pregnancy and Breastfeeding: Because of concerns about possible harm to the developing fetus, PDT is usually avoided during pregnancy. Additionally, breastfeeding may not be recommended; decisions should be made according to the possible risks.

• Ocular Conditions: PDT might not be appropriate in some cases of retinal detachment or other structural problems with the eye.

• Poor General Health: This therapy is contraindicated in persons with comorbidities and poor general health. The patient's general health is a crucial factor, and the procedure might be physically demanding.

What Potential Risks Might the Therapy Pose?

Photodynamic therapy (PDT) is safe and effective in treating various medical conditions. However, similar to any medical procedure, PDT has some risks and side effects. The risks can vary depending on the condition being treated, the photosensitizing agent being used, and the individual characteristics of each patient. Some potential risks associated with PDT include the following:

• Photosensitivity.

• Skin reactions like redness and swelling.

• Pain and discomfort.

• Edema (swelling) of the treated area.

• Scarring.

• Changes in skin pigmentation.

• Infection.

Conclusion

PDT is a common treatment for skin diseases, eye disorders, and some cancers. Many ocular diseases have historically been treated with topical eye drops. Yet efforts have been directed towards creating novel therapeutic devices for ocular drug delivery because of their low efficiency. Effective ocular delivery requires improving drug bioavailability via sustained drug release on the ocular surface. Therapeutic contact lenses are a great substitute for eye drops because of their prolonged drug-release capability.