Based on Cornell University's VHF digital ultrasound scanning prototype and patents, Ultralink LLC (St. Petersburg, FL) has developed a commercial prototype, the Artemis-2 (Figure 1), which will be launched at this year's ASCRS annual meeting in Philadelphia, Pennsylvania. This new device is designed to help ophthalmologists in all disciplines, particularly those in refractive, cataract, and presbyopic surgery, to improve their anatomical diagnosis for surgical planning, and better perform postoperative diagnostic monitoring. The Artemis-2, which uses VHF Arc-scan technology, features high-resolution imaging and measurement capabilities with micronic precision.
The Artemis-2 is the first digital VHF ultrasound arc B-scanner. It can follow the contour of the cornea from one end to the other, and its digital signal processing produces very high-resolution epithelium and flap imaging capability in one scan sweep (Figure 2, below). The system is able to measure important surgical elements, including (1) the thickness of the epithelium within 1 µm, (2) the flap and the bed in a 3-D manner, (3) the anterior and posterior chamber dimensions, including angle-to-angle and sulcus-to-sulcus diameters, and (4) it produces high-resolution imaging of anterior segment structures for glaucoma, tumors, and trauma. Measurements are combined by software to produce a 3-D map of the thickness profile of each corneal layer. Dan Z. Reinstein, MD, coinventor of the Artemis-2 technology, says, “To date, there appears to be no other single technology offering such a wide range of applications. This system answers every surgeon's dream: to delineate the anatomy of the tissue that he or she is about to alter, and shows him or her what is going on beneath the surface.”
PHAKIC IOL SURGERY
The most immediate impact the Artemis-2 is expected to have on ophthalmology will most likely relate to the sizing of IOLs, particularly phakic intraocular lenses (PIOLs). By providing exact sulcus-to-sulcus and angle-to-angle measurements, the Artemis-2 has the potential to increase the safety of both anterior and posterior chamber PIOLs by improving the accuracy of lens sizing—a crucial issue for the long-term safety of these devices (Figure 3, below). Until recently, surgeons have been using the external white-to-white measurement to estimate the internal angle-to-angle or sulcus-to-sulcus diameters. However, last year, Cornell University colleagues Dr. Reinstein, Director of Research in Refractive Surgery, and Artemis-2 coinventor, Ronald Silverman, MD, PhD, Professor of Computer Science in Ophthalmology, conducted a study in myopic eyes. The study revealed no statistical correlation between the external white-to-white measurements and the internal angle-to-angle or sulcus-to-sulcus measurements of the eye. No statistical correlation means that PIOL sizing would be improved by using one size only, based on the average sulcus-to-sulcus or angle-to-angle diameter for all eyes, than by varying the size according to the patient's external white-to-white measurement.
According to Dr. Reinstein, judging internal ocular measurements by measuring the external structure can be quite a gamble. ?Using the patient's white-to-white measurements to guide lens sizing will lead to more over- or undersizing than using only one-size-fits-all measurements,? he says. These new findings may be unsettling for lens companies that have been recommending the use of the white-to-white measurements in order to size PIOLs. Dr. Reinstein notes that because ophthalmologists have learned that ?one-size-fits-all? is inadequate for appropriate lens safety levels, angle-to-angle and sulcus-to-sulcus measurements will have to be measured directly to ensure the greatest safety in PIOL surgery. To date, the Artemis-2 is the only technology that can provide both of these measurements directly.
THE SAFETY FACTOR
Dr. Reinstein believes that the Artemis-2 technology will transform and modernize the safety of PIOLs, as incorrect lens sizing can lead to long-term complications. The ability to monitor the position of posterior chamber lenses intraoperatively and immediately postoperatively has the potential of greatly increasing the long-term safety of these devices. For example, a lens that exerts pressure on the zonules in the ciliary sulcus, or whose haptics are malpositioned behind the iris (and therefore not detectable at the slit-lamp), may not perform as well as a lens that is perfectly placed. Dr. Reinstein says, ?I am convinced that improving the safety profile of PIOLs by accurate anatomical surgical planning and postoperative monitoring could finally position these lenses as a real alternative treatment for correcting lower refractive errors. Currently, extraocular corneal refractive surgery is the first-line approach.?
ARTEMIS-2 IN THE CLINICAL SETTING
The Artemis-2 machine is designed similarly to other diagnostic devices: the patient sits in front of it and places his or her chin on a chin rest. The main difference in the Artemis-2 design compared to the classic ultrasound water bath setup is a novel reverse-immersion design. The patient places his or her eye in an eyecup resembling a swimming goggle, and then a sterile coupling fluid medium fills the compartment in front of the eye and the surgeon performs the scanning without the need for a speculum. There is no contact between the scanner and the eye. While the patient is positioned in the scanner, a coaxial infrared camera enables the operator to visually determine the exact position of the eye during scanning. This also enables the doctor to know exactly where he or she is scanning, and relate the measurements on the scan to the location on the eye. Performing a 3-D scan set requires only 1 or 2 minutes. The scan data for determining internal measurements, or determining the internal positioning of the IOL, are displayed instantaneously on a screen. Mapping of the individual layers of the cornea is performed by software, and a display (the Reinstein Diagnostic Pachymetry) provides thickness maps of the epithelium, stroma, flap, and residual stromal layer, as well as difference maps showing epithelial thickness changes (relating to regression), and stromal thickness changes (relating to tissue ablation depth and biomechanical changes). (To view the Reinstein Diagnostic Pachymetry Display of LASIK, please visit our Web site, www.crstoday.com, and click on the title of this article.) Surgeons can use the Artemis-2 before, during, and after surgery. Prior to surgery, they may use the unit to confirm the patient's intraocular dimensions, to verify the appropriate lens size for insertion. Similarly, corneal thickness before LASIK, or residual stromal thickness after LASIK are determined as important safety parameters for laser refractive surgery. The surgeon can also use the Artemis-2 equipment during IOL surgery. If the surgeon uses a small incision, employing the sterile barrier provided to scan with the Artemis-2, he or she could scan the anterior segment to check for lens position and possibly return immediately to the operating table for a repositioning maneuver. After surgery, the Artemis-2 can be used to monitor the position of the lens over time, to ensure that it remains safely positioned within the eye.
Although the Artemis-2 is still a prototype, a production model is currently under development. David Brown, MD, of Ft. Meyers, Florida, is one of the first ophthalmologists to use the Artemis-2 prototype, and has ordered a production model that he expects to receive this June. “I think this is really a giant leap in terms of technology because you can get very accurate measurements in different layers of the cornea. It also measures anterior chamber depths and crystalline lens thickness, and it images the angle very well. You can't compare it to any one device that we use in ophthalmology, it incorporates many different instruments into one complete package,” says Dr. Brown. Philippe Sourdille, of Nantes, France, is also using an Artemis unit. “One of my strongest convictions is that VHF digital ultrasound will be the slit-lamp of the 21st century,” Dr. Sourdille states. Richard Foulkes, MD, in Chicago, IL, says that the Artemis-2 is allowing surgeons to see parts of the eye in which they were previously working blindly. “The inability to see what we are doing affects almost every area of our field. It's an enormous problem. Now, we have a device that provides these brilliant 3-D images that tell us where we are.”
OTHER OPHTHALMIC APPLICATIONS
The Artemis-2 technology has potential applications outside of cataract and refractive surgery, in glaucoma, cataract, tumor, and retinal subspecialties. The system may also help surgeons better understand the mechanism and required structural elements of nonpenetrating trabeculectomy. Additional diagnostic utilities may include differentiating ciliary body cysts from tumors, diagnosing hypotony due to small ciliary body detachment, analyzing anterior segment trauma, and detecting foreign bodies, according to Dr. Reinstein.
Dr. Reinstein hopes that the Artemis-2 technology will solve the dilemma of physicians creating flaps and inserting lenses without the ability to preoperatively determine the exact biometry of the operative tissues.
?I have had the privilege of using this technology in my refractive practice for the last 5 years. My colleagues and I have conducted, presented, and published many studies on the use of this ultrasound technology, in areas such as ectasia and flap thickness characteristics, biomechanics within the cornea, and epithelial wound-healing dynamics,? Dr. Reinstein says. ?All of these issues are going to be essential if we want to truly customize corneal ablations, or offer the highest safety for PIOLs.? Considering the potential for customized corneal ablations using diagnostic wavefront-sensing devices, Dr. Reinstein believes that accurately pinpointing epithelial and biomechanical changes within the cornea will play an important role in greatly improving the results of corneal surgery. ?We are still not operating on the cornea in a way that is individually predictive; we currently do not alter surgery based on an individual's corneal anatomy. True individualization of corneal refractive surgery will only be achieved once we have an accurate, preoperative 3-D mapping of corneal thickness,? he states. Dr. Reinstein explains that this information, combined with accurate flap thickness and tissue removal characteristics, will allow surgeons to predict the biomechanical effect that the surgery will have on the cornea.
Dr. Reinstein is studying whether surgeons might be able to predict an epithelial response for individual patients, and he says his data look promising. “We are currently spending a great deal of time into this area of research, trying to find ways in which we can predict which eyes are more likely to have more epithelial regression than others. Our findings have shown that there may be a formula for predicting these responses,” says Dr. Reinstein. He hypothesizes that such information could potentially reduce enhancement rates by allowing surgeons to more accurately alter the corneal contour.Dan Z. Reinstein, MD, MA (Cantab), FRCSC, practices in London, England. Dr. Reinstein is Assistant Professor of Clinical Ophthalmology and Director of Research in Refractive Surgery at the Weill Medical College of Cornell University, New York. He also serves as Professeur Associé, Centre Hospitalier National d'Ophthalmologie des Quinzes-Vingts, Paris, France. Dr. Reinstein may be reached at +44 20 7681 1233; firstname.lastname@example.org