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Handheld Imager Poised to Provide New Insights into Eye and Brain Diseases

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Portable instrument captures detailed images of photoreceptors in eyes
of young children

Researchers have developed and demonstrated the first handheld
ophthalmology instrument with resolution-boosting adaptive optics
technology that can image individual photoreceptors in the eye. The new
portable instrument will allow improved diagnosis of eye diseases and
could enable early detection of brain-related diseases and trauma.

In Optica, The Optical Society's journal for high impact research, the
researchers report their new light-weight instrument, which measures
just 10 by 5 by 14 centimeters. They tested the device in children and
adults, demonstrating its ability to capture images of even the very
small photoreceptors close to the center of the retina that play a key
role in vision.

Photoreceptors, specialized neurons that convert light entering the eye
into signals sent to the brain, are the only neurons in the body that
can be imaged non-invasively. Imaging photoreceptors is not only
important for diagnosing eye diseases but could also provide insights
into processes occurring in the brain. Preliminary studies have shown
that changes in the retina can be observed during the early stages of
diseases such as Alzheimer's and after traumatic brain injuries such as
concussions.

"Until now, the imaging systems required for high resolution
photoreceptor imaging consisted of large, heavy components on an optical
table that could only be used with cooperative adults sitting upright,"
said research team leader Sina Farsiu from the Departments of Biomedical
Engineering and Ophthalmology at Duke University, North Carolina, USA.
"Our portable handheld system could expand this important imaging
technique to children and infants, as well as to adults who may not be
able to sit upright and stare straight ahead."

The system could be used on people who are in a reclined position as
they undergo surgery, for example, Farsiu's team reports. It could also
help doctors rapidly assess possible brain trauma, such as in football
players coming off the field with head injuries.

"Because of the limited resolution of MRI — the standard method for
imaging the brain in living people— MRI-based assessment of disease or
trauma to the brain cannot be done at the level of individual cells,"
said Farsiu. "In the retina however, individual photoreceptors can be
imaged at 100 times higher resolution than using brain imaging, allowing
very subtle changes to be seen."

Shrinking the optics

To image photoreceptors today doctors commonly use a device known as an
adaptive optics scanning laser ophthalmoscope (AOSLO). Although adaptive
optics greatly improves the resolution compared to a standard scanning
laser ophthalmoscope, the optical components required also increase the
size, weight and cost of the overall system.

Adaptive optics technology increases image quality by using an optical
component called a wavefront sensor to detect light distortion caused by
the eye. A deformable mirror that quickly changes shape is then used to
compensate for the detected light distortion, leading to clearer images.

To shrink the components within an AOSLO, the researchers developed a
new algorithm to perform wavefront sensing. "Other researchers have
shown that the wavefront sensor can be replaced by an algorithm, but
these algorithms haven't been fast enough to be used in a hand-held
device," said Farsiu. "The algorithm we developed is much faster than
previously used techniques and just as accurate."

The researchers also incorporated a commercially available MEMS-based
deformable mirror measuring just 10.5 millimeters in diameter. "The
optical and mechanical design combined with our new algorithm made it
possible to create the handheld device," said Duke optics expert and
team member Joseph Izatt. "Adaptive optics systems are very sensitive to
slight vibrations or motions, but we designed our system to be very
stable. The optics stay aligned when the system is transported, and it
can also compensate for hand motions during use."

Imaging in people

They used their new system, called HAOSLO for hand-held AOSLO, to image
the retinas of 12 healthy adult volunteers and two children under
anesthesia. The application of the system on a 31-month-old child
represents the first use of adaptive optics to image photoreceptors in
children.

Photoreceptors in adult eyes gradually become smaller toward an area at
the center of the retina known as the fovea. The HAOSLO system was able
to image photoreceptors as close as 1.4 degrees eccentric to the fovea,
where photoreceptors have an average spacing of only 4.5 microns. The
closest that had been accomplished without adaptive optics was 3.9
degrees. Before starting large-scale clinical trials with the
instrument, the researchers plan to incorporate additional imaging
modalities useful for detecting disease.

To help other scientists adapt their system for specific applications,
the researchers made the optical and mechanical designs, computational
algorithms and control software for the new HAOSLO system available
online free of cost.

Paper: T. DuBose, D. Nankivil, F. LaRocca, G. Waterman, K. Hagan, J.
Polans, B. Keller, D. Travn-Viet, L. Vajzovic, A.N. Kuo, C. A. Toth, J.
A. Izatt, S. Farsiu, "Handheld Adaptive Optics Scanning Laser
Ophthalmoscope," Optica, 5, 9, pp. 1027- 1036 (2018). DOI: https://doi.org/10.1364/OPTICA.5.001027

About Optica

Optica is an open-access, online-only journal dedicated to the rapid
dissemination of high-impact peer-reviewed research across the entire
spectrum of optics and photonics. Published monthly by The Optical
Society (OSA), Optica provides a forum for pioneering research to be
swiftly accessed by the international community, whether that research
is theoretical or experimental, fundamental or applied. Optica maintains
a distinguished editorial board of more than 50 associate editors from
around the world and is overseen by Editor-in-Chief Alex Gaeta, Columbia
University, USA. For more information, visit Optica.

About The Optical Society

Founded in 1916, The Optical Society (OSA) is the leading professional
organization for scientists, engineers, students and business leaders
who fuel discoveries, shape real-life applications and accelerate
achievements in the science of light. Through world-renowned
publications, meetings and membership initiatives, OSA provides quality
research, inspired interactions and dedicated resources for its
extensive global network of optics and photonics experts. For more
information, visit osa.org.

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