What Are Investigational Therapies?
Macular degeneration is one of the most common eye conditions causing vision loss in older individuals. In macular degeneration, the macula is damaged, causing impairment of central vision. Some people with the condition have their condition progress slowly, with gradual vision loss, while others may have quickly progressing symptoms or sudden vision loss.
Types of macular degeneration
AMD has two subtypes: dry AMD and wet AMD, and treatment can vary depending on the stage and type of AMD. While dry AMD can have early, intermediate, and advanced stages, wet AMD is by definition always considered advanced or late AMD.1Stargardt disease is an inherited type of macular degeneration and often occurs during childhood or adolescence, although can also occur in early adulthood. Myopic macular degeneration, or MMD, is different than wet AMD but shares the abnormal blood vessel growth and is treated similarly.
What are investigational therapies?
There is no cure for macular degeneration, and treatments are often aimed at slowing down the progression of the disease and preserving existing vision. However, treatment efficacy may vary among individuals, and some people may continue to have disease progression despite treatment. Fortunately, there are several new treatments being explored. Investigational therapies are treatments that have not yet been proven to be beneficial but are being investigated as part of a research study. They may or may not become part of accepted, standard treatment regimens. These investigational treatments are not right for everyone – in order to minimize unintentional harm to patients, clinical trials will only enroll individuals with a certain type and severity of macular degeneration.
Many existing treatments are for wet AMD, leaving those with dry AMD searching for treatments. Although treatment options for dry AMD are currently limited, there are many research studies being conducted worldwide in an effort to develop new effective therapies for both dry and wet AMD.
Stem cell therapy
Stem cell therapy is one such investigational therapy, namely the CPBE-RPE1 clinical trials. In AMD, loss of vision occurs when photoreceptor cells die. These cells receive support and nourishment from neighboring retinal pigmented epithelial (RPE) cells. Therefore, when RPE cells fail or die, photoreceptors also die and vision becomes impaired.2 Some labs have been able to grow new RPE cells from human embryonic stem cells; the idea is to replace the damaged RPE cells in AMD and Stargardt disease with new RPE cells, and also replace the damaged Bruch’s membrane underneath the RPE cells.2,3 Stem-cell therapy is a long-term endeavor, though, and a long-term clinical trial is needed, with a multi-disciplinary approach.4 Stem cell therapies and gene replacement therapies are also being explored for Stargardt disease.3
Inflammation plays a role in dry AMD, and drugs that help reduce or prevent inflammation may play an important role in treatment. Corticosteroids have anti-inflammatory properties and there is a clinical trial investigating the effect of sustained-release fluocinolone acetonide (a long-acting steroid) on the progression of AMD.4 There are also other anti-inflammatory medications being studied, as well as modulators of the complement cascade, which may play a part in the inflammatory response and could be a potential target for intervention in dry AMD.
Vasodilators are drugs that help to dilate, or open, blood vessels. This is thought to be of benefit in dry AMD because choroidal blood flow is reduced in older individuals, and if choroidal blood flow were improved, perhaps disease progression might be slowed.4 Some clinical trials have been performed already on drugs such as alprostadil, with promising results, however, more studies need to be done in order to confirm the initial studies and ensure medication safety.3 Other vasodilators studied such as sildenafil and moxaverine had unclear results and therefore more information is needed.4 This might also be helpful for those with MMD.
There are several drugs with a neuroprotective effect on retinal cells, some of which have been used to lower eye pressure in glaucoma patients such as brimonidine, but are now also being studied for use in AMD.4 There are several other drugs are being investigated for protective effects on various cells within the eye, but need to be studied further to evaluate their full effects.
Becoming involved in clinical trials
If you’re interested in whether you might be a candidate for investigational therapies, talk with your eye doctor about the potential for enrolling in a clinical trial. Clinical trials aren’t for everyone and don’t necessarily guarantee effective treatment. It’s important to also remember that the journey from investigative treatments to accepted, standardized treatments can be a long one, and that it’s important that the therapies get fully vetted and explored, in terms of efficacy, side effects, long-term effects, and generalizability. Your doctor can provide you with more information, as well as advise you about any new breakthroughs regarding investigational therapies.