vision defect is a mismatch between the eye’s focal
distance the range at which it can actually bring
objects into focus and the distance of the object it’s
trying to focus on. Essentially, the new display
simulates an image at the correct focal distance
somewhere between the display and the viewer’s eye.
The difficulty with this approach is that simulating a
single pixel in the virtual image requires multiple
pixels of the physical display. The angle at which light
should seem to arrive from the simulated image is
sharper than the angle at which light would arrive from
the same image displayed on the screen. So the physical
pixels projecting light to the right side of the pupil
have to be offset to the left, and the pixels projecting
light to the left side of the pupil have to be offset to
The use of multiple on-screen pixels to simulate a
single virtual pixel would drastically reduce the image
resolution. But this problem turns out to be very
similar to a problem that Wetzstein, Raskar, and
colleagues solved in their 3-D displays, which also had
to project different images at different angles.
The researchers discovered that there is, in fact, a
great deal of redundancy between the images required to
simulate different viewing angles. The algorithm that
computes the image to be displayed onscreen can exploit
that redundancy, allowing individual screen pixels to
participate simultaneously in the projection of
different viewing angles. The MIT and Berkeley
researchers were able to adapt that algorithm to the
problem of vision correction, so the new display incurs
only a modest loss in resolution.
the researchers’ prototype, however, display pixels do
have to be masked from the parts of the pupil for which
they’re not intended. That requires that a transparency
patterned with an array of pinholes be laid over the
screen, blocking more than half the light it emits.
But early versions of the 3-D display faced the same
problem, and the MIT researchers solved it by instead
using two liquid-crystal displays (LCDs) in parallel.
Carefully tailoring the images displayed on the LCDs to
each other allows the system to mask perspectives while
letting much more light pass through. Wetzstein
envisions that commercial versions of a
vision-correcting screen would use the same technique.
Indeed, he says, the same screens could both display 3-D
content and correct for vision defects, all
glasses-free. They could also reproduce another Camera
Culture project, which diagnoses vision defects. So the
same device could, in effect, determine the user’s
prescription and automatically correct for it.
“Most people in mainstream optics would have said,
‘Oh, this is impossible,’” says Chris Dainty, a
professor at the University College London Institute
of Ophthalmology and Moorfields Eye Hospital. “But
Ramesh’s group has the art of making the apparently