Electromagnetic deformable mirror assists in retinal diagnostics

November 15, 2008
Ilya Petrou, MD

The novel technology found at the heart of an adaptive optics flood illumination fundus camera (AOFIFC, INOVEO)-an electromagnetic deformable mirror (Mirao 52-e, Imagine Eyes)-is designed to facilitate the acquisition of even higher resolution images than those captured by optical coherence tomography systems.

Key Points

Créteil, France-An electromagnetic deformable mirror (Mirao 52-e, Imagine Eyes) used in conjunction with an adaptive optics flood illumination fundus camera (AOFIFC, INOVEO) can assist in more accurate diagnoses of ophthalmic diseases and conditions, monitor their progression, and, ultimately, help in prescribing more targeted treatments that may positively affect prognoses, according to Gisele Soubrane, MD, professor and chief of the Department of Ophthalmology at the Centre Hospitalier Intercommunal de Créteil, Créteil, France.

The electromagnetic mirror effectively reduces the impact of ocular aberrations on imaging, offering much clearer and more detailed images of the retina and its anatomy. These aberrations can include astigmatism and myopia as well as the irregular optical defects found in every human eye.

"As part of the AOFIFC, [the electromagnetic mirror] virtually 'wipes out' the optical aberrations that affect every human eye to varying degrees, thereby degrading the quality of retinal images," Dr. Soubrane said. "The AOFIFC provides us with exquisitely sharp images of retinal microstructures. For example, in patients with refractive disorders such as astigmatism or myopia, the conception of the device is such that the light entering the eye will be 'straightened-out' after it has been altered during its course through the human optical system, thereby producing much sharper images."

"[The electromagnetic mirror] has not yet been coupled with a clinical OCT instrument; however, we are very excited to see because the images that this technology combination will produce, as we expect an even higher resolution than that provided by conventional OCT," she said. According to Dr. Soubrane, the mirror distinctly raises the bar not only in terms of the image quality but also in terms of versatility and depth of field.

Compensating for the eye's optical aberrations, the device enables quality images of the retina's cellular structures. In addition, the AOFIFC employs infrared light for imaging, meaning that not only can the cone cells be imaged and their numbers accurately counted but their viability and metabolism also may be assessed in the near future.

"In some ocular diseases, the numbers of cones are decreased and, using this device, we are able to evaluate the status of the cells and see how well these cells are functioning-in vivo," she said. "[The electromagnetic mirror] enables the AOFIFC to offer us information down to the cellular level. This is proving to be clinically invaluable, assisting us in diagnosis, prognosis, as well as therapies for certain ocular diseases and disorders. Progression of a disease can be much more effectively tracked with this device, something that is crucial for a more favorable prognosis."

Currently, the rods cannot be imaged due to their small size. According to Dr. Soubrane, these cells may also be imaged in the future if another wavelength is used and/or if the mirror is coupled and adapted with a magnifying device or system to image these retinal cells better.

Prior to the advent of the AOFIFC, investigative clinical retinal imaging was performed using fundus cameras, scanning laser ophthalmoscopes, or OCT; some of these had been previously enhanced with adaptive optics in restrictive laboratory settings. The mirror and the AOFIFC offer a different imaging perspective by substituting the high axial resolution achieved using OCT with more detail along the lateral axes. The two technologies will work well together to offer a quality image of the retina, both in terms of resolution and depth, providing physicians with a refined diagnostic tool for identifying and managing ocular diseases, she said.

Several retinal diseases exist in which the etiology of the pathology remains elusive, and, according to Dr. Soubrane, knowing the exact pathogenesis of a disease is crucial in delivering targeted treatment.

"The hope is that the AOFIFC will let us discover the etiology of dysfunctional retinal cells and offer us a deeper understanding of their pathology," she said. "This may, in turn, allow us to delve into the origins of numerous ocular diseases."

The mirror improves the resolution, contrast, and definition of retinal images, allowing for a six-fold improvement in their lateral resolution, from approximately 15 to 20 µm to 3 µm. Dr. Soubrane said that the one downside of the AOFIFC's images is that the visual field available to stimulate the patient's fixation is not large enough (20°), and that this aspect of the imaging could use some improvement and fine-tuning.

She said that there is a need to experiment with other wavelengths in order to facilitate the evaluation of cells other than photoreceptors, including bipolar and ganglion cells, which may shed additional light on the influx of signals sent from the retina to the brain.

Application for glaucoma

The AOFIFC also may see applications in the diagnosis of glaucoma by elucidating which cells are damaged, while providing information into the disease's progression. That information, in turn, may offer insight when choosing appropriate preventive treatments designed to spare these cells from disease and death. According to Dr. Soubrane, the new conventional wisdom is that glaucoma is not simply an issue of increased IOP; it is important to analyze the cellular damage around the optic nerve that may, in turn, offer some insight to the disease's etiology. The cellular definition that the AOFIFC offers may make this evaluation possible, she said.

"It is very important to have an in vivo cellular view, not only for accurate diagnosis of intraocular diseases but also for comprehending their progression. A deeper understanding of these pathologies at the cellular level will soon assist us in treating them much more effectively," Dr. Soubrane concluded.

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