Introduction

What is age-related macular degeneration?

Age-related macular degeneration (AMD) is a disease that affects the eyes.¹ It makes your central vision blurry. Your central vision is extremely important as it helps us to read, see faces and pictures, and identify shapes and colours clearly. The macula is what provides the central vision and is found in the retina. AMD is caused when ageing damages the macula.

AMD is quite common and the main cause of vision loss in the elderly. It does not result in full blindness, but it does make it more difficult to see faces, drive, and anything that requires close focus, like cooking. It can occur slowly or quickly; however, it varies for each individual and may not be detected straight away, so regular eye tests are extremely important. 

Types of age-related macular degeneration

AMD can be divided into early, intermediate, or late stages. In the early and intermediate stages, AMD usually has no symptoms and vision loss isn’t typically seen. This is normally detected by an eye test, as the optometrist (the person doing the eye test) will be able to see damage to the macula.²

The late stages of AMD have two further types, dry and wet. The types are based on what is seen during the eye test. 

Dry AMD

Dry AMD means there is a loss of central vision due to cells in the macula not working anymore. This type is more common compared to wet. It happens quite slowly, and there are gradual changes to your vision, which can take years before the last stages are reached. Once this point has arrived, it causes part of the centre vision to disappear or become dark. It does not cause blindness, as your peripheral vision stays normal. Some people may go on to develop the wet form of AMD. 

Wet AMD

A smaller percentage of people have wet AMD and usually have dry AMD first. Wet AMD happens when the cells of the macula do not function normally, and new blood vessels are made to try to make up for those cells. These blood vessels do not grow in the right places and cause swelling below the macula. This damages the macula, resulting in scarring and a loss of your central vision. It can develop quite rapidly and can damage your central vision over days or weeks. It also does not cause complete blindness as the peripheral vision remains intact. 

What is photodynamic therapy?

Photodynamic therapy (PDT) is typically used to treat cancer. It uses a drug that is sensitive to light as well as a bright light. You can either be given a cream or a drug that makes the cells in your body sensitive to light. It contains a chemical that is sensitive to visible light, such as daylight (known as a photosensitizer). Once the cream/drug is taken, a doctor shines a light, which destroys cancer/damaged cells. PDT is only given to the damaged area. There is usually inflammation, but once this is cleared up, there is a big improvement, and sometimes there is a complete cure. 

PDT in AMD

Photodynamic therapy is a possible treatment option for those suffering from the wet type of AMD. It cannot restore vision that has been lost, but it can slow down the rate of damage to your central vision. It is not the first line of treatment given, as there are drugs that can help. A medicine that is sensitive to light is injected. It goes to the blood vessels that build up under the macula. A laser is shone onto the affected eye, which activates the medicine. It creates a blood clot in the vessels, which cuts it off. As a result, further vision loss can be prevented. 

When and why is PDT used to treat AMD?

• PDT is only used to treat the wet type of AMD. It’s used when there is a particular pattern of the blood vessels, and when there is a greater than 50% that they have clear borders to target
• It is not the go-to treatment; usually, an anti-VEGF injection is given, as they have a better response
• PDT is typically used if other first-line treatments have not worked, such as the anti-VEGF injections
• It may be used as an alternative if people are unable to get the anti-VEGF injections, for example, people who have recently had a stroke or heart attack are unlikely to get the injections
• PDT is used to slow the progression of AMD by targeting and destroying the abnormal blood vessels, slowing down the rate of vision loss
• The aim of PDT is to try to maintain the remaining vision by stopping further degeneration (it can restore vision that has already been lost)
• PDT may be preferred to anti-VEGF injections as these injections need to be given monthly during the beginning, whilst PDT can be given every few months instead. This may be better for those who struggle with frequent trips to the hospital³

PDT procedure⁴

What happens before the procedure?

• Firstly, the patient needs to be assessed. An eye exam will be done, and some imaging is also needed, for example, fluorescein angiography 
• Before photodynamic therapy is given, the risks and benefits are explained in detail. Before any therapy can be given, a consent form needs to be signed
• Once this has been completed, eye drops are given to dilate the pupils so the retina can be more accessible 
• The eyes need to be protected after the procedure is done. Sunglasses are given as the eyes become sensitive to light for a short while after 

Photosensitising agent

• The photosensitising agent is injected and takes about 10 minutes to be infused
• After it has been infused, it takes around 15 minutes for it to reach the blood vessels in the eye

Light activation

• A laser is set up to activate the photosensitising agent 
• The eye is prepared, and a contact lens is put in place, which focuses the laser light
• The laser is applied to the part of the retina that has the abnormal blood vessels 
• The photosensitising agent is activated and makes oxygen molecules that destroy the abnormal blood vessels

How often is the treatment given?

• One session can take up to 30 mins
• At the beginning, PDT is given every 3 months for around two years
• Follow-up appointments are given every month or so to assess if further treatment is needed
• How often and how many times photodynamic therapy is given is dependent on each person and how advanced the macular degeneration is

Side effects

Photodynamic therapy is a generally safe treatment for age-related macular degeneration. These symptoms are usually temporary and can last up to a few weeks. The most common ones are:⁵

• Temporary changes to vision- vision may become blurry for a couple of days or weeks
• Photosensitivity- the eyes become more reactive and sensitive to light; bright lights need to be avoided
• Discomfort around the eyes- there may be pain or swelling around the eyes
• Reactions- in rare cases, some may react to the photosensitising agent
• Headaches
• Back pain from infusions

Future directions

PDT is not the first treatment you would receive to treat AMD, but it can play a huge role in the management of wet AMD. There is ongoing research to improve the therapy, for example:⁶

• Combination therapies- PDT can be combined with other treatments, such as anti-VEGF drugs, which may lead to a faster reduction in vision loss over time
• Better photosensitisers- new photosensitising agents that have increased performance and fewer side effects will improve how effective the therapy is as a whole
• Delivery- the way the drug is delivered could be even more precise and targeted so that it reaches only the abnormal blood vessels, also reducing side effects as a result
• Personalised treatments- research into environmental and genetic factors can lead to a personalised PDT treatment 
• Stem cell therapy- stem cells can be used to potentially regenerate damaged retinal tissue to help restore vision loss. This, along with PDT, can be a huge advance in the treatment options available

Summary

Age-related macular degeneration affects older people’s eyes. It causes the loss of central vision due to the macula being damaged. It does not cause full blindness, as the peripheral vision remains intact and normal. It can, however, disrupt your daily routine greatly; for example, it may be more difficult to recognise faces. One treatment option for the wet type of AMD is photodynamic therapy. 

PDT is an alternative treatment option for wet AMD, especially for those for whom the standard first-line treatment of anti-VEGF injections has not helped or when they are not suitable for it. It involves injecting a drug that is sensitive to light. This reaches the abnormal blood vessels found near the macula via the bloodstream. A laser is used to activate the photosensitising agent that destroys the abnormal blood vessels. PDT aims to reduce the rate of progression and reduce worsening vision loss. 

PDT can act as a treatment for AMD, but requires regular sessions for about two years with regular follow-up appointments. It cannot restore lost vision, but it improves the quality of life for those suffering from age-related macular degeneration.