Figure 4. Strategies for restoring vision.

(A) In the late stages of IRDs, when most/all photoreceptors are gone, efforts to replace them from external and internal sources are underway. In external cell replacement, photoreceptor progenitors are derived from retinal organoids. In internal cell replacement, Müller glial reprogramming could allow for photoreceptor regeneration.

(B) Optogenetic approaches to vision restoration convert second or third-order neurons into light sensors. A variety of optogenetic actuators, including microbial opsin (e.g., ChrimsonR), animal opsins, chimeras (e.g., Opto-mGluR6), and photosensitized glutamate receptors (Li-GluR) are being tested.

(C) Retinal prosthesis can be implanted subretinally or epiretinally and either receive data and power from external sources or be directly driven by light (i.e., photovoltaic arrays). In addition to retinal prostheses, cortical prostheses, and cognitive assistants may restore vision and replace visual functions, respectively.