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Hand-Held Device Inspects Individual Retina Cells

Haoslo device

Handheld adaptive optics scanning laser ophthalmoscope (Theodore DuBose, Duke University)

24 August 2018. A medical engineering team created a small lightweight device that can inspect individual photoreceptor cells in the retina, the part of the eye that converts visual images to brain signals. Researchers from Duke University describe the system and tests with adults and children as young as infants in yesterday’s issue of the journal Optica.

The team from Duke’s Vision and Image Processing Laboratory, led by biomedical engineering professor Sina Farsiu, is seeking to advance adaptive optics technology that aims to correct distortions in images often from distant or the tiniest light sources, and thus is applied to astronomy as well as ophthalmology. In ophthalmology, lasers are used in adaptive optics to provide a reference beam for correcting distortions in examining photoreceptor cells in the retina that convert light energy to electrical signals via the optic nerve to the brain.

This device is known today as an adaptive optics scanning laser ophthalmoscope, or Aoslo. Today’s Aoslo systems are non-invasive devices to detect disruptions in photoreceptor cells that indicate damage from neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease, as well as traumatic brain injuries. These table-sized non-invasive systems work fine in clinics with adults who can sit still and gaze forward for several minutes, to provide images with a higher resolution than MRI scans. But they are difficult to use with children and adult patients not able to control their movements.

The Duke team developed an alternative device they call a hand-held adaptive optics scanning laser ophthalmoscope, or Haoslo. To shrink the technology to this size, the researchers replaced a key component in today’s Aoslo systems, the wavefront sensor, with an algorithm to calculate the distortion. A wavefront is the surface of an advancing light wave, with its area and shape determined by the source of that wave, and the sensor readings instruct a deformable mirror to compensate and correct the distorted image.

Farsiu tells the Optical Society, publisher of the journal, “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.” He adds that “The algorithm we developed is much faster than previously used techniques and just as accurate.” The researchers also use a commercially-available microelectronic deformable mirror, only 10.5 millimeters in diameter. The result is an Haoslo device weighing less than 8 ounces and measuring 4 by 2 by 5.5 inches.

The team tested the Haoslo device with 12 adults and 2 children under anesthesia, with results that show the system can return images of individual photoreceptors, even in the center of the retina, where the cells are smaller and vision is most acute. The researchers believe the device can be used to test infants, particularly those born prematurely, for eye disorders and follow a child’s brain development. The system could also be used to quickly diagnose athletes for concussions on the bench or sidelines. In addition, its small size provides eye surgeons with an additional tool in the operating room, rather than waiting for tests conducted later on.

The team plans to test the device further with other potential disorders before evaluating it in larger clinical trials. In the meantime, the researchers make the Haoslo device’s design specifications, algorithm, and software freely available on the university web site.

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