Ocular Gene Therapy: A Literature Review With Focus on Current Clinical Trials

Gene therapy has been one of the most researched topics in the last decade. It has now become a revolutionized therapeutic tool of modern medicine. Gene therapy is the alteration of the defective gene involved in the disease process in the host cells. It delivers therapeutic genetic information via modified viral or non-viral vectors. Ocular gene therapy, in particular, has progressed in treating inherited retinal diseases since the eye is a favourable organ for gene therapy development. The advantage of the eye as a target for gene therapy is attributed to its easy accessibility and blood-ocular barrier. Several ongoing clinical trials are investigating various gene therapies for other ocular diseases, including neovascular age-related macular degeneration, retinitis pigmentosa (RP), Usher syndrome, glaucoma, and several others. However, there are challenges such as ocular inflammation and humoral response, infection by the viral vectors, and insertional mutagenesis. These limitations depend on several factors; whether viral or non-viral vectors are used, which viral vectors were used, the route of administration, whether subretinal, intravitreal, or suprachoroidal, and the dose of vectors and the target tissue. These complications may lead to therapeutic failure and vision loss due to intraocular inflammation. This review aims to summarize existing knowledge about ocular gene therapy and the associated limitations we face, with a special focus on a few ongoing clinical trials.