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Imaging of retinal cells possible with new OCT technique
By interfacing a specialized deformable mirror with OCT, researchers have been able to acquire three-dimensional photoreceptor images.
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Clinicians may be closer to getting retinal images on a cellular level through work combining adaptive optics with three-dimensional ultra-high resolution optical coherence tomography, according to one researcher.
Wolfgang Drexler, PhD, and his team at Cardiff University have discovered the benefits of interfacing the mirao 52-d Electromagnetic Deformable Mirror (Imagine Eyes) with optical coherence tomography (OCT) machines to enhance imaging resolution.
“From a scientific point of view, adaptive optics, especially with the performance of the Imagine Eyes mirror, has pushed the whole vision science and ophthalmic imaging field,” he told Ocular Surgery News during a telephone interview.
Last year, Dr. Drexler and his team showed some of the first images of retina microstructures garnered from a living human eye with this technique, according to a press release from Imagine Eyes.
The images, which include three-dimensional views of photoreceptors, demonstrate the potential this technique has for the early detection of diseases that are worldwide leading causes for blindness.
“If you could see ganglion cells, photoreceptor cells, small capillaries or the nerve fibers, this is something that clinicians would like to see for improved early diagnosis,” he said. “Adaptive optics is an interesting technique that will have, with this technology, a huge clinical impact in vision science and in ophthalmic imaging.”
Compensating for ocular aberrations
According to Dr. Drexler, standard high-axial resolution OCT lacks a high-quality transverse resolution, which is required to get cellular detail. Theoretically, an increase in the laser beam diameter of the imaging device should solve this problem.
“If you image the retina, the cornea and the lens act as an imaging objective, so the easiest way to have a perfect, small spot on the retina and therefore have good transverse resolution is to increase the beam diameter,” he said.
However, he said aberrations in the cornea and the lens would introduce significant wavefront aberrations and worsen the focus accomplished at the retina.
The deformable mirror from Imagine Eyes allows Dr. Drexler to compensate for extremely high aberrations in order to get a small, well-focused spot size.
“You build an inverse wavefront of the investigated eye with your deformable mirror and therefore correct the aberrations in the eye at the same time you perform OCT imaging,” he said.
Dr. Drexler said it was the quality of this particular deformable mirror that allowed him to develop this new imaging technique.
“The quality of your correcting device strongly depends on how good your deformable mirror can be deformed to correct highly aberrated eyes,” he said.
The number of actuators in a deformable mirror and the amount of micrometers the reflective surface can be pushed back and forth (its stroke) are what determine the quality of the mirror. The deformable mirror from Imagine Eyes has 52 actuators and a stroke of 50 µm.
“The deformable mirror of Imagine Eyes is unique in terms of having enough actuators in this deformable mirror and having a unique, unprecedented stroke,” Dr. Drexler said.
Looking ahead
Although the prospects for this new technique are apparent, Dr. Drexler said the actual clinical diagnostic impact on major retinal diseases of the technique on ophthalmic imaging remains to be determined.
“In principle, if you integrate adaptive optics into any ophthalmic diagnostic technique, it should give you much more information, therefore better diagnosis,” he said. “But to the best of my knowledge, it hasn’t been firmly proven that adaptive optics integrated into any kind of fundus photography or scanning laser ophthalmoscope or OCT significantly improves diagnostic information.”
However, he did say that the higher quality of current deformable mirrors makes it easier to envision interfacing adaptive optics with diagnostic ophthalmic techniques.
“It’s easier for adaptive optics to have a clinical impact in more simple ophthalmic imaging techniques because to interface adaptive optics in the fundus camera or in a scanning laser ophthalmoscope is a little bit easier than integrating it into high-end OCT systems,” he said.
For more information:
- Wolfgang Drexler, PhD, can be reached at the Department of Optometry & Vision Sciences, Cardiff University, Redwood Building, King Edward VII Ave., Cathays Park, Cardiff CF10 3NB, Wales, United Kingdom; +44-29-20780-230; fax: +44-29-20-780-231; e-mail: drexlerw@cf.ac.uk. He has no financial interest in the mirao 52-d Electromagnetic Deformable Mirror or in Imagine Eyes.
- Imagine Eyes, maker of the mirao 52-d Electromagnetic Deformable Mirror, can be reached at 18 rue Charles de Gaulle, 91400 Orsay, France; +33-1-64-86-15-66; fax: +33-1-69-07-53-79; Web site: www.imagine-eyes.com.
- Jared Schultz is an OSN Staff Writer who covers all aspects of ophthalmology. He focuses geographically on Europe and the Asia-Pacific region.