VHF Digital Ultrasound Arc-Scanning
"Performing refractive surgery without VHF digital ultrasound scanning is akin to an orthopedic surgeon performing surgery without an X-ray."
History:
Beginnings
In 1991, Dr. Reinstein was invited to begin a Research Fellowship with Dr. D Jackson Coleman, Professor and Chair of the world-acclaimed Bio-acoustic Research Facility at the Department of Ophthalmology of Cornell University. At that time, VHF ultrasound technology was in it's infancy and researchers were applying the imaging technology to study glaucoma and tumors of the eye. Dr. Reinstein set out to modify and develop the then current prototype together with Ronald H. Silverman, PhD, Professor of Computer Science at Cornell University in order to be able to scan the cornea.
Bioengineering Science
Dr. Reinstein and co-workers were the first to of digital signal processing techniques on VHF ultrasound. For the first time in history, it was possible to accurately measure the surface layer of the cornea: the epithelium. The first reports of this achievement were published in the Archives of Ophthalmology and the Journal of Corneal and Refractive Surgery both in 1993. Dr. Reinstein's seminal publication in the journal Ophthalmology in 1994 was the first described method of mapping the thickness of the epithelium in 3D. This opened up a new field of research: actually measuring the response of the corneal surface to excimer laser surgery.
Clinical Research: LASIK
Until that time, the whole world believed that in LASIK, because the surface epithelial layer was not physically touched by the surgery, there would be no epithelial changes. Dr. Reinstein was the first researcher to prove that not only the epithelial layer changed in every single eye treated by LASIK, it did so in a way that was optically significant. These findings were presented at international meetings between 1995 and 1996 and were published in Ophthalmology in 1999. It became evident that without the ability to predict these changes, it would be impossible to improve the accuracy of LASIK beyond a certain limit. Then in the year 2000, at the annual meeting of the Association for Research in Vision and Ophthalmology (ARVO) Dr. Reinstein presented the first ever clinical data demonstrating that a cornea undergoing LASIK became modified from a mechanical standpoint, and that a significant portion of the intended refractive effect was lost to unpredicted elastic changes within the cornea. These biomechanical changes together with epithelial dynamics will form the basis for all customized or individualized LASIK and PRK treatments. Furthermore, the correction of the complications of corneal refractive surgery will be largely dependent on this information. The Reinstein Institute has secured a leading position in this field of research and is working hard toward the goal of perfecting LASIK.
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Clinical Research: Phakic IOL technology
Dr. Reinstein and colleagues were the first to publish VHF digital ultrasound scanning of a lens implant known as a "phakic intra-ocular lens" in the American Journal of Ophthalmology, 1997. This is a technology that is not as of yet approved by the FDA, but has been in development in Europe and South America for the last 10 years. The correction of myopia or hyperopia is effected by the insertion of a thin lens inside the eye through a small incision in the cornea. This artificial lens is implanted either in front of the iris (pupil) or behind the iris. The greatest safety issue involving phakic lens implants is that of proper sizing. Currently, surgeons use external measurements of the eye (such as the diameter of the cornea) to predict the internal dimensions of the eye. Unfortunately, in about 1% of cases the sizing is off by an amount so significant that serious consequences can ensue. - The eye can develop glaucoma or cataract necessitating further surgical or medical intervention to prevent blindness. VHF digital ultrasound scanning is the first method available to accurately measure the internal dimensions of the eye to within one-tenth of a millimeter. With this level of accuracy in surgical planning, it is hoped to enable phakic intra-ocular lens placement safely.
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Artemis is a very high frequency (VHF) ultrasound eye scanner designed and built by Scott Phillips Engineering[email-link], based on the original prototype by Dr. Reinstein and colleagues. In use, the patient leans forward placing their head onto an adjustable headrest. The headrest's unique design permits the patient to pull away quickly from the scanner if desired. An eyecup filled with a saline-based interface fluid couples the ultrasound signal to the eye, while a precision mechanism moves the transducer past the front of the eye. During the accurately controlled arc motion of the transducer, which lasts less than one second, many thousands of ultrasound samples are digitized. Following a scan, signal analysis is performed on a PC-compatible microcomputer, and the data are available for immediate viewing on an LCD monitor or archival storage to disc media.
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Artemis display during wide-angle arc scanning of anterior segment.The B-mode image on the lower right (taken in a horizontal plane) shows the full anterior segment anatomy, allowing visualization from angle-to-angle and sulcus-to-sulcus. Images of this kind can provide precision measurements crucial for lens implantation.
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Control Panel:
Artemis display during scanning. At upper left is shown the real-time infra-red video image of the eye which is in total darkness during scanning. This is used for proper alignment of the scan axis. To the right is shown the real-time A-scan display. This represents echo amplitudes along the current line-of-sight of the ultrasound transducer. On the lower left is shown a schematic depicting the programmed geometry of the scan set. In this case, four scans offset at 45-degree intervals are to be acquired. The current scan plane (shown in red) is in the horizontal axis. The image on the lower right is an arc B-scan of the cornea taken in the horizontal plane of the right cornea.
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Data from Artemis scans provide:
High-resolution B-scan image of the front of the eye showing the cornea, anterior chamber, iris (forming the pupil) and the natural lens behind it. High precision measurements for planning intraocular lens surgery provided include:
- Anterior chamber structures, angle-to-angle distance
- Posterior chamber structures, sulcus-to-sulcus distance
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The figure shows a cornea before (A) and after (B) LASIK. Note the new interface (I) showing the flap after LASIK.
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High precision biometry within the cornea including:
- 3D flap thickness mapping
- 3D residual stromal bed thickness mapping
- 3D anterior segment angle-to-angle
- 3D posterior segment sulcus-to-sulcus measurement
- 3D corneal thickness mapping
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