Will it ever be possible to restore vision to a patient of Norrie disease?
I think at some point of time it will be. I don’t know if this will happen in my lifetime, but the research leading up to it is certainly very fascinating.
There appear to be two problems which need to be addressed. Firstly, the optics in the eye, i.e. the detached retina, and secondly, the neuronal circuitry in the visual cortex (the part of the brain which is responsible for seeing).
In this post, I talk about the first problem. The problem relating to the visual cortex will be taken up in a subsequent post.
[Aside: Although in a typical case of Norrie the blindness is complete (i.e. no light perception), there are a few cases of Norrie in our online community where the affected person has some light perception. It is probable that the neuronal circuitry in these individuals is well developed and so that would be one less problem to worry about in this subset of the community.]
To restore the visual circuitry in the eye, we would either have to put a new retina in place, or come up with a solution which bypasses the retina. Going by current research, there appear to be the following 3 possibilities:
- Cortical implant
- Retina transplant
- Whole eye transplant (no, I’m not joking, there is such a project underway)
Cortical implant
This approach to restoring vision bypasses the eye (& the optic nerve) completely.
Cortical implants (also known as IntraCortical Visual Prostheses – ICVPs) aim to provide patients with visual information by stimulating neurons in the brain’s visual areas. An ICVP comprises a digital camera on a glasses frame. The camera is connected (either by a wire or wirelessly) to a small computerized vision processor, which is kept in a pocket or worn on a belt. Images from the camera are transmitted to the processor which in turn converts them into waveform patterns, which are then transmitted wirelessly to the implant in the brain. The implant is typically a chip that is implanted into the visual cortex (located at the back of the brain).
It must be stated that a cortical implant will provide “artificial” vision - a pixelated version allowing the user to perform elementary visual tasks such as navigation and object recognition. Depending on the number of electrodes on the implant, it might even allow for reading large print and recognizing people.
Groups developing ICVPs include the following:
- Monash Vision Group in Melbourne, Australia
- Illinois Institute of Technology
- École Polytechnique de Montreal in Canada
- Second Sight Medical Products, California
A press release from Second Sight states that the first human clinical trials are planned to commence by the end of the first quarter of 2017.
Human trials for the Monash University’s ICVP are expected to take place sometime in 2016 according to an article published in the Sydney Morning Herald.
The above list is not exhaustive. ICVPs are being created by a few other groups as well. One such group is the Visual Prosthesis Lab at Massachusetts General Hospital. A notable difference here is that this group proposes to implant the electrodes in the lateral geniculate nucleus (LGN) and not the visual cortex. The LGN is a relay center on the visual pathway. It is located in the thalamus (a structure in the middle of the brain). We can think of the visual pathway like this:
Retina --------- LGN --------- Visual Cortex
There are pros and cons of this approach versus the one which places the implant on the visual cortex. One obvious difficulty is in getting to the LGN since it is located deep inside the brain, whereas the visual cortex, being located at the back of the brain, is easily accessed.
Retina transplant
Researchers have succeeded in creating functional three-dimensional retinal organoids using stem-cells.
An organoid is a three-dimensional organ-bud grown in vitro that shows realistic micro-anatomy. The technique for growing organoids has rapidly improved since the early 2010s, and it was named by The Scientist as one of the biggest scientific advancements of 2013.
[Source: Wikipedia]
The organoids show the architectural organization of the retina, and include functioning photoreceptor cells capable of responding to light.
However, in order to have a retinal model which resembles the real thing, the lab grown organoid needs to (1) include a network of blood vessels, and (2) be able to transmit the electrical impulses which can be interpreted by the brain as images. Once this happens - or if this happens - retina transplantation will perhaps become a reality.
Researchers who have successfully created retinal organoids:
- Dr. Masayo Takahashi, Professor of ophthalmology, RIKEN Center for Developmental Biology, Kobe, Japan
Media coverage:
- Dr. Maria Valeria Canto-Soler, Assistant Professor of ophthalmology at the Johns Hopkins University School of Medicine
Media coverage:
Mini-Retina Created with Stem Cells, June 2014
Light-Sensing Retina in a Dish, June 2014
- Dr. Mike O. Karl, Research Group Leader, German Center for Neurodegenerative Diseases (DZNE), Dresden, Germany
Media coverage:
Whole eye transplant
The U.S. Department of Defense has awarded $1.25 million to University of Pittsburgh School of Medicine (UPMC) researchers co-led by McGowan Institute for Regenerative Medicine faculty members Dr. Vijay Gorantla, associate professor of surgery in the Department of Plastic Surgery at the University of Pittsburgh and the administrative medical director of the Pittsburgh Reconstructive Transplant Program at UPMC, and Dr. Joel Schuman, chair of the Department of Ophthalmology, Pitt School of Medicine, and director of the UPMC Eye Center, to establish the groundwork for the nation’s first whole-eye transplantation program.
The Pitt researchers will lead a multidisciplinary consortium (dubbed the Audacious Restorative Goals in Ocular Sciences (ARGOS) Consortium) that includes clinicians and scientists from Harvard University and the University of California, San Diego.
In the following excerpt from an article published online, Dr. Jeffrey Goldberg, director of research at the Shiley Eye Center at University of California, San Diego, and Dr. Vijay Gorantla talk about the main problem with a whole eye transplant, that of reconnecting the optic nerve:
"The chief problem," Goldberg explained, "is that when you switch out an eyeball you have to completely cut all connections between the optic nerve and the eye. So then you need to reconnect the donor eye's nerve fibers back to the recipient's brain in order to achieve vision restoration. But we know that once you make that cut, the nerve fibers just do not regrow on their own. That doesn't happen automatically."
"That's what distinguishes an eye transplant from most other types of transplants," Gorantla added. In other organ transplants, the chief hurdle is simply reconnecting a proper blood supply. "For example, if you get the plumbing connected and the blood going, then a transplanted heart will beat in the recipient patient immediately," Gorantla said.
"But an eye transplant actually has more parallels with a hand or face transplant," he said. The eye may appear healthy because of a renewed blood supply, but without reconnecting the optic nerve, "there's no motor activity and no sensation or eyesight," Gorantla said. "The result is functionless and lifeless."
Luckily, various laboratories "have made significant progress" in fostering the long distance regrowth of nerve fibers, Goldberg said. "In animals with optic nerve injury or degeneration we've even started to see fibers regrow all the way back to the brain," he noted.
You can read more about this project by clicking on the following links:
UPMC exploring future of eye transplants - Pittsburgh Post-Gazette, July 2015
Second Sight - Science Magazine, March 2015
And with that I wrap up today's post.
Till next time then,
Meenu.
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