Adaptive optics reveals fine details of retinal structure

05 Sep 2018

Duke University handheld platform assists diagnosis of eye disease and trauma.

A portable instrument able to image individual photoreceptors in the eye could allow improved diagnosis of eye disease and early detection of eye- and brain-related diseases.

Adaptive optics scanning laser ophthalmoscopes (AOSLO) have been used for some time by clinicians to examine the eye, employing adaptive optics to remove optical aberrations from images obtained using a confocal laser scanning microscope.

These devices have until now been large in size and limited to imaging adult subjects, but a team at Duke University has designed what is said to be the first portable handheld system. The new HAOSLO platform, weighting less than 200 grams, was described in Optica.

"The imaging systems required for high resolution photoreceptor imaging have consisted of large, heavy components on an optical table that could only be used with cooperative adults sitting upright," said Sina Farsiu of Duke University. "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."

In its paper, the team noted that recent advances in wavefront sensorless AO technology were a key aspect of reducing the footprint and weight of AOSLO platforms.

Conventional AO measures the incoming wavefront directly and uses that information to control a deformable mirror positioned to counter the distortions, but wavefront sensorless AO employs algorithms to examine a series of aberrated images, assessing the optimizations needed from the physical properties of the images themselves.

Eye and brain diseases

"To overcome the weight and size restrictions in integrating AOSLO into handheld form, we used recent advancements in the miniaturization of deformable mirror technology and 2D microelectromechanical systems (MEMS) scanning, together with a novel wavefront sensorless AO algorithm and a custom optical and mechanical design," commented the team in the Optica paper.

The new probe and associated numerical methods could be useful for a variety of applications in ophthalmic imaging, and the Duke team has made its designs and computational algorithms available as open source data for other researchers.

In trials, HAOSLO was used to examine the retinas of 12 adult patients and two children, including a 31-month-old infant who represented the first use of adaptive optics to image photoreceptors in a child, according to the Duke team. The system was able to image photoreceptors as close as 1.4 degrees eccentric to the fovea area of the retina, where photoreceptors have an average spacing of 4.5 microns. Without AO, the closest measurement had previously been 3.9 degrees.

Further clinical trials with the instrument will follow, and the researchers plan to incorporate additional imaging modalities into the platform that could prove useful for detecting other diseases. Brain trauma could be one example, if HAOSLO is able to observe the small changes in the retina that can result from such injuries.

"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."