A new route to Retinal Displays - Holographic Lenses
Retinal display systems have been under development for many years with few successes. They are a type of display system whereby the interface writes light data directly onto the back of the eye, bypassing the eye's normal mechanisms. There are many advantages to this approach, including eliminating eye-strain caused by the eye re-focussing to look at something that appears to be far away when it is part of a fixed-distance display, and for ocular disabilities, the ability to bypass whichever eye-mechanism is non-functional, to restore full vision as long as the retina is intact.
Through the years, a variety of laser-driven methods have been attempted, with various workarounds to deal with the small problem that a mis-focussed laser display can cause burn damage to the retina itself. itself.
A new, and fundamentally different approach to the problem is now being trialled by researchers at the Technion-Israel Institute of Technology. Professor Shy Shoham and team are testing the power of holography to artificially stimulate cells in the retina of the eye, with the intent of bionically restoring vision. As a side-effect it would of course create a whole new class of retinal displays.
The medical intent of their system is to combine optogenetics gene therapy to deliver light-sensitive proteins to damaged retinal nerve cells. The retinal display system then forces visual data onto these cells in an effort to activate them.
Intense pulses of light can activate nerve cells newly sensitized by this gene
therapy approach. But Shoham said researchers around the world are still searching
for the best way to deliver the light patterns so that the retina sees
or responds in a nearly normal way.
In their paper in the February 26 issue of Nature Communications, the Technion researchers show how light from computer-generated holography could be used to stimulate these repaired cells in mouse retinas. The key, they say, is to use a light stimulus that is intense, precise, and can trigger activity across a variety of cells all at once.
Holography, what we're using, has the advantage of being relatively precise and intense, Shoham said. And you need those two things to see.
The researchers turned to holography after exploring other options, including laser deflectors and digital displays used in many portable projectors to stimulate these cells. Both methods had their drawbacks, Shoham said.
Digital light displays can stimulate many nerve cells at once, but they have low light intensity and very low light efficiency, Shoham said. The genetically repaired cells are less sensitive to light than normal healthy retinal cells, so they preferably need a bright light source like a laser to be activated.
Lasers give intensity, but they can't give the parallel projection that would simultaneously stimulate all of the cells needed to see a complete picture, Shoham noted. Holography is a way of getting the best of both worlds.
The researchers have tested the potential of holographic stimulation in retinal cells in the lab, and have done some preliminary work with the technology in living mice with damaged retinal cells. The experiments show that holography can provide reliable and simultaneous stimulation of multiple cells at millisecond speeds.