Two studies by researchers at the University of Birmingham have shown that delivering drugs against the wet form of age-related macular degeneration (AMD) in the form of eyedrops might soon be possible in humans [1, 2].
What is age-related macular degeneration?
AMD is a pathology of the retina, which is a light-sensitive tissue located in the back of the eye and is similar to the film in a non-digital camera. Two-dimensional images are created on the retina and are subsequently transferred to the brain in the form of electrical neural impulses. Near the center of the retina is the macula, an oval-shaped region responsible for central, high-resolution, color vision. In AMD, the macula is damaged, impairing or preventing this kind of vision. AMD is progressive, but it cannot lead to total blindness, as it doesn’t affect peripheral vision. It comes in two forms, wet and dry, with the latter being overwhelmingly more common and, unfortunately, presently incurable. As the name suggests, the highest risk factor for AMD is age; the disease is usually observed only in patients over 50.
Dry AMD appears to be caused by the accumulation of a metabolic waste compound known as A2E, and while there are no currently approved therapies for this condition, Ichor Therapeutics is currently working on a potential treatment called LysoCLEAR.
The wet form impairs vision through the abnormal growth of fragile blood vessels that tend to leak blood and proteins below the macula, which eventually causes damage to photoreceptor cells and leads to vision loss if untreated. Wet AMD might progress from dry AMD, but this is more rare, with most wet AMD cases happening on their own. The wet form of the disease can be treated with laser coagulation or with injections of the drugs bevacizumab and ranibizumab. According to Birmingham researchers, costly and impractical injections might soon be replaced by the more convenient self-administration of eyedrops.
The two studies
Intraocular injections have thus far been the only effective way to deliver drugs to the back of the eye, but aside from being more expensive and requiring frequent visits to the clinic, they’re understandably uncomfortable; for these reasons, researchers have long looked for a way to deliver therapeutically sufficient amounts of anti-AMD drugs to the back of the eye through drops.
In their first study , the scientists showed that the cell-penetrating peptides they use to deliver the drugs were nontoxic and could be delivered in clinically relevant amounts to live mice and rats, and this novel method even proved more effective than laser treatment. Similar results were achieved in the second study , in which this method was tested on rabbit eyes in vivo and on porcine eyes ex vivo; this second step is significant in that rabbit and porcine eyes are more similar to human eyes than mouse or rat eyes.
The researchers are currently working with a US company to turn their discovery into a viable therapeutic avenue for AMD patients, and more studies to further prove the validity of this approach are being conducted. Clinical trials are likely to follow suit soon afterwards, possibly in spring 2019.
 de Cogan, F., Hill, L. J., Lynch, A., Morgan-Warren, P. J., Lechner, J., Berwick, M. R., … & Logan, A. (2017). Topical delivery of anti-VEGF drugs to the ocular posterior segment using cell-penetrating peptides. Investigative ophthalmology & visual science, 58(5), 2578-2590.
 de Cogan, F., Lynch, A., Berwick, M., Peacock, A., Elsherbiny, S., Xu, H., & Chen, M. (2018). Topical treatment for AMD: Non-invasive delivery and efficacy of ranibizumab and bevacizumab in rabbit and porcine eyes. Investigative Ophthalmology & Visual Science, 59(9), 1439-1439.