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Hand-Held Imager Could Broaden Use of AOSLO

Photonics.com
Aug 2018
DURHAM, N.C., Aug. 27, 2018 — Researchers at Duke University have miniaturized adaptive optics (AO) technology to develop a portable hand-held ophthalmology device that can image individual photoreceptors in the eye at high resolution. The new instrument could allow improved diagnosis of eye diseases to a larger population and enable early detection of brain-related diseases and trauma.

To image photoreceptors, doctors commonly use an AO scanning laser ophthalmoscope (AOSLO). Current-generation AOSLOs have a large footprint and are limited to imaging patients who are able to sit upright and fix their gaze for several minutes.

Handheld portable adaptive optics scanning laser ophthalmoscope, Duke University.
A new hand-held ophthalmology instrument allows imaging of photoreceptors in the eyes of young children, as pictured here. It could help to improve the diagnosis of eye diseases and eventually find use in early detection of brain-related diseases and trauma. Courtesy of Theodore DuBose, Duke University.

To shrink the size, weight, and cost of the AOSLO and extend its application, researchers designed what they believe to be the first portable hand-held AOSLO (HAOSLO) system. The team transformed the AOSLO into a hand-held probe by improving its optical signal processing and mechanical designs. This included development of a new algorithm that replaces the AOSLO’s large wavefront sensing system.

“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 researcher Theodore DuBose. “The algorithm we developed is much faster than previously used techniques and just as accurate.”

Wavefront sensing is used in the AOSLO to detect light distortion caused by the eye, and a deformable mirror is used to compensate for the detected light distortion, leading to clearer images. In place of a bulky mirror, the researchers incorporated a commercially available MEMS-based deformable mirror measuring just 10.5 mm in diameter into their design.

The new system measures just 4 in. × 2 in. × 5.5 in. and weighs less than half a pound.

Handheld portable adaptive optics scanning laser ophthalmoscope, Duke University.
The hand-held adaptive optics scanning laser ophthalmoscope weighs about the same as a large mobile phone. It can be used to image individual photoreceptors in people. Courtesy of Theodore DuBose, Duke University.

“The optical and mechanical design combined with our new algorithm made it possible to create the hand-held device,” said professor 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."

HAOSLO was used to image the retinas of 12 healthy adult volunteers and two children under anesthesia. According to the researchers, the application of the system on a 31-month-old child represents the first use of AO to image photoreceptors in children.

“Our new tool is fast and lightweight, so physicians can take it directly to their patients, and the probe allows us to collect images quickly, even if there is movement,” said professor Sina Farsiu. “These capabilities allow us to open up the pool of patients who could benefit from this technology.”

The system could be used on people who are in a reclined position as they undergo surgery, for example. It could also help doctors rapidly assess possible brain traumas, such as in football players coming off the field with head injuries. A noninvasive tool, the HAOSLO, like the AOSLO, provides a significantly higher resolution than an MRI.

Before the researchers prepare for large-scale clinical trials, they plan to incorporate additional imaging modes for detecting other diseases.

The team at Duke has made the optical and mechanical designs, algorithms, and control software for the new HAOSLO system available online free of cost, so that other scientists can adapt the new system for their scientific applications.

The research was published in Optica, a publication of OSA, The Optical Society (doi: 10.1364/OPTICA.5.001027).

GLOSSARY
probe
Acronym for profile resolution obtained by excitation. In its simplest form, probe involves the overlap of two counter-propagating laser pulses of appropriate wavelength, such that one pulse selectively populates a given excited state of the species of interest while the other measures the increase in absorption due to the increase in the degree of excitation.
adaptive optics
Optical components or assemblies whose performance is monitored and controlled so as to compensate for aberrations, static or dynamic perturbations such as thermal, mechanical and acoustical disturbances, or to adapt to changing conditions, needs or missions. The most familiar example is the "rubber mirror,'' whose surface shape, and thus reflective qualities, can be controlled by electromechanical means. See also active optics; phase conjugation.
ophthalmology
The branch of medicine involved in the study of the anatomy, functions, diseases and treatments of the eye.
Research & TechnologyeducationAmericasimagingprobeHandheld Probeportable deviceopticsadaptive opticsophthalmologyBiophotonicsoptical designmedicinemedicaladaptive optics scanning laser ophthalmoscopephotoreceptors

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