As discussed in the text, the eye can be divided into anterior and posterior segments with different diseases characteristic of these segments. Diseases that would be potentially treated with stem cell–based therapies include corneal opacification (image reproduced with permission from the New England Journal of Medicine; ref. 9) and glaucoma (enlarged optic nerve head cup/disc ratio). Glaucoma is typically considered a disease of the anterior segment, since treatments have historically been directed at decreasing fluid production or increasing fluid outflow by targeting the ciliary body or TM, respectively. The vision-threatening pathology, however, is in the posterior segment principally affecting the ganglion cells and optic nerve. In the posterior segment, degenerative neuronal diseases could include those affecting photoreceptors such as retinitis pigmentosa and the photoreceptors and retinal pigmented epithelium such as atrophic macular degeneration. Retinal vascular diseases of the posterior segment would include DR and neovascular macular degeneration.