The authors’ major goal was to improve gene therapy of vision restoration considering light damage. So far the most popular microbial opsin version is ChR. The blue light intensity to activate ChR is high and may induce photo chemical damage. Here they chose ReaChR, a red -shifted channelrhodopsin variant instead of ChR. The authors reported their work that ReaChR, a channelrhodopsin from the species of Chloromonas oogama , can restore light response in the retina of mice, macaque and human explants. In vivo recordings were performed on the retina of mice, macaque and human explants. And animals behavior tests were performed on the ReaChR-treated mice.

The article proved ReaChR can restore light responses on the retina of mice, macaque and human explants in longer wavelength light condition comparing to ChR. This article confirms a feasible and safer option, ReaChR, to the optogenetic gene therapy toolbox. This article provided their originality on that they transfected the human retina explant and recorded responses successfully.

Major points in the article which needs clarification, refinement, reanalysis, rewrites and/or additional information and suggestions for what could be done to improve the article. 1. In figure 8, the author claimed the left and right are the same human explant. But the blood vessel trace were actually different. If they were the same piece of tissue, at the site electrodes # 1 and #2, there were no GFP positive cells. And on the sites with strong GFP expression, there were no signal recorded. 2. In Fig5C the responses showed here is robust, but the cell number was so low. Total 14 cells in three macaque retinae could be recorded with signals. There should be a lot improvement to get better promoters and viral capsids. 3. In fig 5 and 6, the isolation of ganglion cell activities was only recorded with the blocker of L-AP4, but only L-AP4 maybe not enough to block all the responses from upstream activities. To completely isolate the responses from ganglion cells may need more antagonists.

Minor points like figures/tables not being mentioned in the text, a missing reference, typos, and other inconsistencies. 1. In the result section, figure 4C, the normal animal(wild type mouse) showed no preference in the dark side. But the ReaChR-treated mice showed significant preference in the dark even more than the wild type. This result should be discussed in the discussion section. 2. Fig.2B the authors chose the safety threshold at 470 nm as a control, the 470 nm is the peak stimulation for ChR. But the peak stimulation for ReaChR is not 590 nm. Fig. 2D showed the peak stimulation for ReaChR is 540 nm. To compare the safety threshold, maybe 540 nm should be chosen in Fig.2B. 3. Fig2C in the patch clamp recording, the protocol is setting from 650 nm to 400 nm. It will be very interesting to know the responses in the setting from 400 nm to 650 nm. From this stimulation protocol, we would like to know a previous short wavelength stimulation would not inactivate the ReaChR channels. 4. In Fig4 why the wt animal stay longer than ReaChR treated animal? ReaChR treated animals are more sensitive to the light condition? Maybe the adaptation ability was not restored.

Addressing these issues will make this paper more impactful.