Glaucoma is the leading cause of irreversible blindness worldwide. The primary cause of glaucoma is not known, but several risk factors have been identified, including elevated intraocular pressure and age. Loss of vision in glaucoma is caused by the death of retinal ganglion cells (RGCs), the neurons that convey visual information from the retina to the brain. Therapeutic strategies aimed at delaying or halting RGC loss, known as neuroprotection, would be valuable to save vision in glaucoma. In this review, we discuss the significant progress that has been made in the use of gene therapy to understand mechanisms underlying RGC degeneration and to promote the survival of these neurons in experimental models of optic nerve injury. Gene Therapy (2012) 19, 127-136; doi:10.1038/gt.2011; published online 6 October 2011Keywords: retinal ganglion cell; neuroprotection; glaucoma NEUROPROTECTION IN GLAUCOMA: RATIONALE AND CURRENT LIMITATIONS Adult-onset glaucoma is an optic neuropathy that affects more than 50 million people around the world, with 47 million having bilateral (both eyes) blindness due to this disease. As more effective diagnostic tools become available, the number of cases is expected to rise, and a recent study predicts that there will be 70 million people with glaucoma in 2020. 1 Glaucoma is considered to be a group of diseases characterized by progressive optic nerve degeneration that results in visual field loss and irreversible blindness. The cause of glaucoma is unknown, but several risk factors have been identified, including high intraocular pressure, age and genetic predisposition. Open angle and angle-closure glaucoma, the most common forms of the disease, are often associated with high intraocular pressure. A crucial element in the pathophysiology of all forms of glaucoma is the death of retinal ganglion cells (RGCs; Figure 1) and, as these are central nervous system neurons, their loss is irreversible. At present, there is no cure for glaucoma, and the standard treatment is to lower intraocular pressure by medication or surgery. However, a significant proportion of patients continue to experience visual loss even when pharmacological treatments effectively reduce eye pressure. Therefore, novel therapeutic approaches are needed for its treatment and management.Early-onset glaucoma, comprising primary congenital glaucoma and juvenile open-angle glaucoma, has a clear genetic basis. Between 10 and 30% of individuals with juvenile open-angle glaucoma have mutations in the gene encoding myocilin, 2,3 and, on average, B40% of people with primary congenital glaucoma have mutations in the gene encoding cytochrome P450 protein. 4 Both genes are expressed in the trabecular meshwork and ciliary body, and defects in these genes may cause ocular hypertension. The elucidation of the genetic basis underlying adult-onset glaucoma is difficult because the late onset of disease limits the number of individuals available for linkage analysis. However, at least 29 genetic loci for various forms of glaucoma and 12...