Adaptive optics sees retinas clearly

26 Sep 2008

A new retinal imaging system enables cellular-level imaging even in eyes with significant optical aberrations.

Most devices using adaptive optics for retinal imaging are unwieldy and only function in eyes with minimal optical defects. Now INOVEO, a French consortium of 11 industrial, academic and medical researchers, has developed a prototype for ultra-high resolution retinal imaging that uses adaptive optics (AO) to overcome these problems.

The adaptive optics flood illumination camera (AOFIC) integrates a infrared flood illumination system with a mirao-52-e deformable mirror supplied by Imagine Eyes, which uses 52 electromagnetic actuators to deform the mirror's surface up to ±50 µm.

"Other AO retinal imaging projects used subjects with very healthy eyes, but mirao is the only deformable mirror that can compensate for the wide-ranging aberrations that clinicians encounter," Mark Zacharria of Imagine Eyes told optics.org. The AOFIC was even able to capture images of photoreceptor cells of a subject with keratoconus, a disease that causes severe deformation of the cornea.

"The IR flood illumination makes examinations very comfortable as the source is invisible to the subject, doesn't induce blinking and less scattered by the intraocular media," said Zacharria. "We will also be introducing a pupil tracking system to the device in order to improve imaging performance in the presence of eye movements."

The AOFIC prototype is used to visualize the human retina in vivo. The flood illumination system illuminates the retina and takes successive images every 10 ms with a field of view of 4° x 4° at a resolution of 2.5 µm. "Unlike other AO systems, the imaging field is sufficiently large to identify 'landmarks' on the retina, to confirm exactly where the images have been taken from," Zacharria commented.

The AOFIC can complement optical coherence tomography (OCT) examinations, as OCT has excellent axial resolution and can probe deeply into tissue, but has limited transverse resolution so identifying microstructures can be difficult. "The new device will not only improve diagnostics but will enable us to gain understanding into many ocular pathologies such as age-related macular degeneration and quite possibly glaucoma," said Zacharria.

The first prototype was delivered to the Hôpital Necker in Paris and the second to the Centre Hospitalier Intercommunal de Créteil. A third prototype will be delivered to the Institut de la Vision later this year. The INOVEO team expects the first peer-reviewed scientific publications early next year.