Age-related macular degeneration: Can thermal laser therapy help slow down vision loss?
Thermal laser therapy can reduce vision loss in one type of wet age-related macular degeneration (AMD). But the effect is only noticeable two years after treatment, and the therapy can reduce vision in the short term. This risk could be higher for people with the most common type of wet AMD.
Age-related macular degeneration (AMD) is an eye disease in older people. In industrialized countries AMD is the most common cause of sight loss. The macula is a narrowly defined area of the retina, which is responsible for sharp vision. AMD at first causes a loss of the sharpest and most detailed part of sight, called the “central vision”, and can eventually lead to complete loss of sight. Central vision is important for things like driving or reading. People who have AMD can usually still see around the edges of their field of vision. It is not exactly known what causes AMD.
Wet (neovascular) AMD is where new, abnormal blood vessels grow beneath the retina. There are two types of wet AMD: In the most common type, the abnormal blood vessels grow underneath the center of the retina. That is called subfoveal or central AMD. The fovea is the center of the macula, and “subfoveal” means “underneath the fovea”. If the blood vessels grow outside the fovea, this is called extrafoveal AMD. This type is less common.
Thermal laser therapy (also called laser photocoagulation) is a treatment in which laser rays are focused on the abnormal blood vessels. Heat from the rays is used to damage the abnormal blood vessels and prevent bleeding. More recently, new treatments have been developed that can also be used in subfoveal AMD. These include photodynamic therapy, surgery, and drugs that aim to stop blood vessel growth underneath the center of the retina, too. You can read more about the disease and some other treatment options in our feature on AMD.
Researchers from the Cochrane Collaboration looked for clinical trials that studied the benefits and disadvantages of laser photocoagulation for wet AMD. They found 15 trials, 11 of which looked at the standard form of thermal laser treatment. This treatment aims at the whole affected area. The other trials looked at treatments that are less commonly used, and where only parts of the abnormal blood vessels are targeted.
Altogether there were more than 2,000 people with AMD in these trials. The effects of photocoagulation were measured using standard eye charts. Most of the trials compared laser therapy with having no treatment.
The comparison of photocoagulation of the entire affected area with no treatment showed that after 2 years laser treatment can help to slow down progressive vision loss in some people. Almost half of the people who received no treatment experienced vision loss (49%, or 49 out of 100 of these participants). For people with laser therapy, this number was only 34% (34 out of 100) of the participants. That means that thermal laser therapy prevented vision from getting worse in an extra 15 out of 100 people.
But there was also a disadvantage: immediately after treatment, there was an increased risk of vision loss for a short time. Three months after therapy, an additional 5 out of 100 patients had worse vision than before (17% of patients with laser treatment compared to 12% of patients without laser treatment). This means that people who choose laser treatment need to be prepared for the chance that their sight might get worse for a short time before it gets better later. This is because thermal laser treatment not only seals off blood vessels successfully, but can also damage healthy parts of the eye.
The researchers concluded that the risk of harm caused by the treatment can be high for people with the more common, central type of AMD (subfoveal AMD). Because in this type the abnormal blood vessels are right in the central part of the eye, the laser could cause more damage to the sight. For this reason, thermal laser therapy is normally only used to treat certain cases of extrafoveal AMD.