The Eidon confocal scanner (Centervue).
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Real-color Imaging
The Eidon confocal scanner can scan with white light, resulting in a true-color image (above far left, compared to the same scan [near left]taken using scanning laser ophthalmoscopy, producing a pseudo-color image). Above, right: a sample Eidon wide-field image mosaic. (
Image courtesy Centervue
.)Pros and Cons
Next-generation Ultra Wide-field
Addressing Technical Problems
Optos&#;s California ultra-wide-field scanner (above, left) can perform indocyanine green angiography out to the retinal periphery with almost no peripheral distortion (above, right). (
Image courtesy Optos.
) &#;We took pictures of these eyes using the Optos systems; then we used the new software available on the California to compute the measurements,&#; he continues. &#;We compared them with the known measurements, and they were accurate within 1 percent. It&#;s the first time any fundus camera system has been validated in this way, in terms of the measurements it produces. I think this technology will make a big difference in how we do trials going forward.REVIEW
six months, two new instruments designed to provide high-resolution views of the retina have been approved by the Food and Drug Administration. One is the latest iteration of Optos&#;s wide-field scanning devices; the other is a new instrument from Italy that allows true-color retinal imaging. Here, we review the features offered by each device, with comments from ophthalmologists who have used them in the clinic.The Eidon confocal scanner (Centervue, Padova, Italy) received FDA clearance in December . According to the manufacturer, Eidon is the only wide-view system that combines confocal imaging with natural white-light illumination to provide a true-color image, as opposed to the pseudo-color rendering generated by monochromatic lasers in scanning laser ophthalmoscope-based systems. The merging of color channels in that approach results in a bright orange retinal image, blood having a blue-green hue, and a dark or black optic nerve. (See example, facing page.) Centervue says that white-light illumination reveals greater detail of retinal pathologies and allows a clearer view of the optic nerve.Other benefits of the Eidon, according to Centervue, include:It supports multi-field acquisitions covering up to 110 degrees in automatic mode and 150 degrees in manual mode. (See example, facing page.)Paolo Lanzetta, MD, professor and chairman of the Department of Medical and Biological Sciences-Ophthalmology at the University of Udine, Italy, has used the Eidon at a large-volume ambulatory surgery center in Udine. &#;Eidon is the first true-color scanning ophthalmoscope that uses confocal imaging and white light illumination integrated in a pupil-dilation-free system,&#; he says. &#;We&#;re very enthusiastic about its ability to generate high-quality, high-resolution, real-color pictures. It provides a retinal image that looks exactly as the retina looks when directly observed. This should provide new opportunities for early diagnosis of many retinal conditions.&#;Dr. Lanzetta says he finds the device to be very versatile with its combination of multiple imaging modalities. &#;The instrument and the software interface are user-friendly and easy to learn,&#; he notes. &#;It requires minimal operator involvement; it automatically aligns with the patient&#;s pupil and focuses on the retina. At any time, it&#;s possible to stop the automatic alignment and switch to manual mode using the joystick, allowing us to customize focus and alignment to capture specific pathologies in detail.&#;Dr. Lanzetta sees the Eidon as having some advantages in comparison to both conventional fundus cameras and other wide-field options. &#;Conventional fundus cameras capture color retinal images that are oversatured in the red channel, showing an optic disc that looks washed-out and uniform,&#; he points out. &#;Image acquisition may be limited by media opacities such as cataracts or corneal opacities, and the capture flash can be very disturbing for the patient. SLO systems are able to achieve better contrast compared to conventional fundus photography, but they typically use a single wavelength laser and provide monochromatic images&#;black and white or pseudo-color&#;and thus are unable to extract color information from the retina. A true color, high-resolution retinal image is essential for an accurate diagnosis.&#;Dr. Lanzetta says that his clinic has used Optos&#;s Daytona instrument in the past. &#;Both the Daytona and Eidon are compact in design and extremely easy to use, although positioning the patient&#;s head and capturing the retinal image is easier with Eidon,&#; he says. (The manufacturer notes that the Eidon costs less than half as much as Optos&#;s California.)Dr. Lanzetta says the Eidon does have some limitations. &#;Eidon is an excellent device, but the field of view should be increased,&#; he says. &#;Adding autofluorescence images or fluorescein angiography may provide additional diagnostic information. Also, Eidon&#;s optical system operates within the range of -12 D to +15 D. In eyes with a myopic refractive error of more than 12 D, Eidon may be unable to focus on the posterior pole and detect retinal conditions related to pathological myopia.&#;Despite these limitations, Dr. Lanzetta says the Eidon device could be widely used as a screening tool in the primary-care setting for the detection of ophthalmic diseases such as diabetic retinopathy, glaucoma and age-related macular degeneration. &#;Eidon can be introduced into the daily practice for detecting posterior segment diseases and helping retinal physicians in the diagnosis and management of several retinal conditions,&#; he says. &#;It can easily be used by any type of personnel thanks to its automated mode.&#;Optos&#;s recently approved California instrument is a compact, tabletop device that does non-mydriatic high-resolution ultra wide-field imaging (up to 200 degrees) through many cataracts, and pupils as small as2 mm. According to Optos, other features include:Srinivas R. Sadda, MD, professor of ophthalmology at the David Geffen School of Medicine, University of California, Los Angeles, and director of the Doheny Image Reading Center, says his group has worked with a prototype of the California device prior to its recent FDA approval. (He notes that their prototype is almost identical to the version that was approved.) &#;This device allows us to do fluorescein, indocyanine green angiography, autofluoresence, red-free and pseudo-color testing all on one platform out to the retinal periphery,&#; he says. &#;We&#;ve found it to be very useful in taking care of patients, and it&#;s now being incorporated into a number of different trials.&#;Dr. Sadda says that in his experience, several features of the California are big steps forward. &#;One is that the Optos wide-field platform now has indocyanine green angiography capability,&#; he explains. &#;ICG is important for identifying certain conditions such as polypoidal choroidal vasculopathy, a type of choroidal neovascularization. One of the things that we&#;ve learned from using ultra-wide-field ICG for this purpose is that the lesions can be quite large and extend quite a ways, even past the posterior poles. We also use ICG to aid in the diagnosis and management of patients with central serous chorioretinopathy. Using ultra-wide-field ICG on my patients with CSR, I&#;ve discovered that the choroidal vascular disturbance and hyperpermeability can be quite extensive. This has given us new insights into that disease.&#;Dr. Sadda believes the most significant application for wide-field ICG, especially in the United States, is for the evaluation of uveitis and inflammatory diseases. &#;ICG can highlight a number of lesions that you can&#;t see with other imaging modalities because they tend to be deep lesions or affect the choroid in particular,&#; he explains. &#;Having ultra-wide-field ICG is great because inflammatory diseases that affect the choroid tend to affect the entire retina and extend far beyond the posterior pole. Those are areas we were not able to access before.&#;Dr. Sadda is also impressed that Optos has figured out how to manage the peripheral distortion that&#;s present in retinal images. &#;Any fundus camera will have this distortion,&#; he notes. &#;It can become particularly noticeable in a wide-field fundus camera, and it&#;s not easy to correct for the distortion so that you can get accurate measurements from the images. I run an image-reading center, so things related to image quality and measurements are pretty important.&#;Optos claimed to have resolved this problem with this instrument, so we put it to the test,&#; he continues. &#;We did a project that we published in Ophthalmology a few months ago,in which we used patients who had been implanted with the retinal chip prosthesis&#;an electronic implant that&#;s put on the retina in blind patients with retinal degenerations to help them see. We chose these patients because that chip is of a known size, making it possible to use it as a ruler inside the eye.&#;We took pictures of these eyes using the Optos systems; then we used the new software available on the California to compute the measurements,&#; he continues. &#;We compared them with the known measurements, and they were accurate within 1 percent. It&#;s the first time any fundus camera system has been validated in this way, in terms of the measurements it produces. I think this technology will make a big difference in how we do trials going forward.&#;The California instrument also addresses another common problem with wide-field images: It&#;s harder to see the details in the superior and inferior aspects of the image,&#; he says. &#;The image kind of fades away a bit. In the past we&#;d compensate for this by having the patient look up or down and take another image. Now we don&#;t often do that, because the California device optimizes and maintains the resolution out to the periphery, especially superiorly and inferiorly.&#;Dr. Sadda also likes that the California makes it easy to correlate findings between the different modalities it offers. &#;We&#;ve had a few patients in whom we&#;ve done a fluorescein angiogram and ICG simultaneously,&#; he explains. &#;The instrument doesn&#;t do them at exactly the same time; it alternates the flashes to get them. But they&#;re so close in time that it makes it easier to correlate findings between the two modalities.&#;Dr. Sadda has served as an advisor and consultant to Optos, as well as other imaging companies. His reading center has received research support to support the analysis of images collected in trials and other projects related to retinal imaging. Prof. Lanzetta has no financial interest in any technology cited in this article.
For more than a half-century, ophthalmologists have relied on light to treat retinal disease. After observing the effects of a solar eclipse on patients' retinas, Gerhard (Gerd) Meyer-Schwickerath investigated using natural sunlight to treat retinal disease, first successfully using the technique in to perform a retinal coagulation.1 Unfortunately, the technique was limited by weather conditions, the lengthy exposure time required, and the constantly changing angle of the sun in the sky.
Dr. Meyer-Schwickerath then developed a carbon arc lamp as a more reliable artificial light source; however, a short filament life span, liberation of soot, and unpredictable retinal burns limited its usefulness. In the s, Carl Zeiss Laboratories produced the xenon arc lamp as specified by Dr. Meyer-Schwickerath, which quickly came into widespread use by ophthalmologists for retinal photocoagulation. These units produced light from the passage of a high intensity electrical arc through a chamber filled with xenon gas. It emitted a light spectrum similar to sunlight, with a relatively high, uniform power output. Although this modality was effective, it was difficult to focus the beam precisely to a small spot. Treatments also required a relatively long exposure duration and were painful for the patient.
Furthermore, many complications occurred, such as intense retinal burns, resulting in scarring, fibrous traction, visual field defects, and vitreous hemorrhage. Diminished transparency of any ocular media was a contraindication to xenon arc photocoagulation because the absorption of the visible light by the cornea, lens, or other media opacity caused tremendous heat absorption in that area.
The introduction of the ruby laser in launched the laser era. Lasers offered clinicians much more versatility, with a range of wavelengths and pulse durations, and more precisely targeted treatments. With this milestone, technology evolved rapidly, including concurrent development of various lenses, revolutionizing the treatment of retinal disease.
Read on to learn more about what lasers currently offer clinicians in treating patients with retinal disease.
Michael D. Ober, MD, practices ophthalmology at Retina Consultants of Michigan in Southfield, Michigan. Seenu M. Hariprasad, M.D., is associate professor, director of clinical research, and chief of Vitreo-retinal Service at the University of Chicago, Department of Surgery, Section of Ophthalmology and Visual Science, Chicago, Illinois. Neither Dr. Ober nor Dr. Hariprasad has a financial interest in the products mentioned in this article.Compared with the xenon arc lamp, the ruby laser featured a more controlled delivery of energy, allowing ophthalmologists to manipulate light beams for treatments, creating small chorioretinal scars and reducing the risk of damage to surrounding tissues. Although the ruby laser was attached to a monocular, direct ophthalmoscope, the development of argon and subsequent laser sources permitted ophthalmologists the flexibility of treating patients at the slit lamp, the indirect ophthalmoscope or the operating microscope.
Since the ruby red laser, a number of lasers have been used, including argon, krypton, frequency-doubled Nd:YAG, Er:YAG, excimer, Ti:sapphire, dye lasers, and solid state diode. The introduction of solid state lasers was a major development, with the advantages of being less expensive, compact and portable.
Currently available ophthalmic lasers offer a range of wavelengths, depending on the type. The most common are 532-nm green, 561- or 577-nm yellow, 660- or 670-red, and 810-nm infrared. Although some clinicians prefer a laser with multiple wavelengths, others utilize a single wavelength because multiple-wavelength lasers take more space and carry a heftier price tag.
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It has not been determined that one specific wavelength is most efficacious; however, some wavelengths offer advantages in specific situations. For example, the red laser is useful in patients with a vitreous hemorrhage because it is least absorbed by hemoglobin, and yellow has the benefit of less absorption by macular pigment.
Photocoagulation quickly came into widespread use throughout ophthalmology despite a lack of randomized, controlled studies proving their benefit. In the s and s, several landmark studies were performed that filled this void and confirmed the undeniable therapeutic effect of retinal photocoagulation. Two of these trials, the Diabetic Retinopathy Study and Early Treatment Diabetic Retinopathy Study, were so exceptionally well planned and conducted, with results that forever impacted practice patterns, that they are considered among the best clinical trials conducted in ophthalmology and medicine.
The Diabetic Retinopathy Study (DRS), a prospective, randomized, multicenter clinical trial that began in the s, examined whether panretinal photocoagulation (PRP) is effective in preventing severe vision loss in patients with diabetic retinopathy.2,3 It enrolled one eye of 1,758 patients with proliferative diabetic retinopathy (PDR) or severe nonproliferative diabetic retinopathy (NPDR), which randomly received either argon laser or xenon arc photocoagulation while the other eye was placed in an untreated control group. The study demonstrated that PRP reduces the risk of severe vision loss by at least 50% compared with eyes receiving no treatment. Severe vision loss was defined as visual acuity less than 5/200 at two or more consecutive follow-up visits performed at 4-month intervals. Two years into the study, severe vision loss associated with PDR developed in 16% of control eyes versus 6% of treated eyes. In eyes with high-risk characteristics (Table 1),2,3 the effect was more pronounced, with severe vision loss developing in 26% of control eyes and 11% of treated eyes. Argon laser was found to have equal efficacy to xenon arc but was favored overall because it produced fewer adverse effects.
Table 1. DRS High-Risk Characteristics2,3 &#; Neovascularization of the optic disc at least one-fourth to one-third disc areas in sizeFigure 1. Laser technology has evolved considerably from the humble beginnings of the xenon arc lamp (above).
The Early Treatment Diabetic Retinopathy Study (ETDRS), a prospective, randomized, multicenter clinical trial that enrolled patients between and , examined whether focal photocoagulation was effective in treating diabetic macular edema,4,5 whether aspirin affected the course of diabetic retinopathy,6 and when PRP treatment should begin.7
In this study, 1,508 eyes were randomly chosen to immediately receive focal or panretinal photocoagulation, and treatment was deferred in 1,490 eyes. Patients were randomly chosen to receive 650 mg/day of aspirin or placebo. Follow-up continued for 1 year in 80% of eyes and at least 3 years in 35%.
The study reported that the risk of persistent macular edema and significant visual loss decreased by approximately 50% in eyes treated with focal laser photocoagulation. At 1 year of follow-up, 5% of eyes treated with focal photocoagulation had moderate visual loss (defined as doubling of the visual angle or loss of 15 letters) compared with 8% of eyes with deferred treatment; at 2 years, 7% of eyes treated with focal photocoagulation had moderate visual loss compared with 16% of deferred; and at 3 years, 12% of eyes treated with focal photocoagulation had moderate visual loss compared with 24% of deferred eyes. However, the reduction in risk of moderate vision loss was more pronounced in patients with clinically significant macular edema (CSME): 1% in treated eyes versus 8% in deferred eyes at 1 year, 6% in treated eyes versus 16% in deferred eyes at 2 years, and 13% in treated eyes versus 33% in deferred eyes at 3 years (Table 2).4,5 Researchers concluded that focal photocoagulation was effective in reducing the risk of moderate visual loss for patients with CSME.
Table 2. Definition of Clinically Significant Macular Edema in ETDRS4,5 &#; Thickening of the retina at or within 500 microns of the center of the maculaFigure 2. Proliferative diabetic retinopathy after panretinal photocoagulation. The DRS concluded that PRP reduces risk of severe vision loss by at least 50%.
Figure 3. Retinal tear after laser therapy.
The study also found that aspirin did not alter the effects of focal laser treatment or prevent progression to PDR.6 It further concluded that early scatter photocoagulation was not recommended for patients with mild or moderate nonproliferative diabetic retinopathy.7
Twenty-eight years after the ETDRS trial began, the Diabetic Retinopathy Clinical Research Network published a landmark paper that confirmed the visual benefits of focal laser photocoagulation.8 The study was a randomized, multicenter clinical trial comparing the efficacy and safety of 1-mg and 4-mg doses of intravitreal triamcinolone (Trivaris, Allergan Pharmaceuticals, Irvine, CA) with focal/grid photocoagulation in the treatment of diabetic macular edema with foveal involvement in 840 eyes. Four months after treatment, mean visual acuity was better in the group treated with 4 mg triamcinolone than in the group treated with 1 mg triamcinolone or laser; however, at 16 months and 2 years, mean visual acuity was significantly better in laser-treated eyes than either intravitreal triamcinolone group. This result confirmed that lasers remain the gold standard treatment for diabetic macular edema, despite advances in pharmacologic treatments.
Despite the proven efficacy of laser treatment and initially rapid advances in laser technology, over the last 20 years lasers have not kept pace with technological advancement in other areas. A comparison with retinal imaging technologies, where modalities such as optical coherence tomography (OCT) and fundus photography have shown rapid advancement, confirms the relative stagnation in laser delivery systems. Economic factors confronting laser manufacturers may have limited research and development for this modality. Lasers today are sold outright and often last beyond their intended lifetime with many units functioning well over 10 years past their purchase date. Without innovation and technological advances, there is little incentive for physicians to trade in or purchase new equipment. The lack of capital return to laser manufacturers in turn decreases available funding for research and development continuing the cycle.
The most recent developments generally have focused on laser adjustments such as spot size, power, and pulse duration. These adjustments are typically available in most laser delivery systems that have been available for the last 15 years. For example, to reduce heat accumulation and retinal damage, laser manufacturers have conducted research to determine whether units that provide short-duration pulses at higher power achieve the same results. However, clinicians may be able to use their existing lasers similarly, making adjustments for shorter pulse durations and higher power levels. Even if research shows less damage using shorter durations, physicians may not have to purchase new technology when a duration as short as 0.01 seconds has been available on models available for many years.
In , OptiMedica (Santa Clara, Calif.) introduced a unique platform that represents one of the only recent major advances in a laser delivery system with the Pascal pattern scan laser photocoagulator. It is a 532-nm laser used for standard photocoagulation procedures that can apply a uniform pattern of as many as 56 spots in 0.6 seconds. OptiMedica reports that the Pascal laser allows ophthalmologists to perform macular grid treatments effectively and panretinal photocoagulation more rapidly than conventional lasers.
Ellex (Minneapolis, Minn.) introduced the Integre Duo, which features red and green wavelengths in a single unit, and soon will introduce the Integre Pro, with yellow and red wavelengths in a single unit. Quantel Medical (Bozeman, Mont.) recently released a single laser delivery system with four individual wavelengths (532-nm green, 577-nm yellow, 660-nm red, and 810-nm infrared). This is the only commercially available system we are aware of with all four wavelengths in one unit.
Several companies currently sell laser delivery systems with multi-wavelength platforms (usually 532-nm green, 561-nm yellow, and 660-nm red), including Lumenis (Santa Clara, Calif.), Nidek (Fremont, Calif.), and Carl-Zeiss Meditec (Dublin, Calif.). Iridex (Mountain View, Calif.) makes individual 532-nm green and 810-nm infrared lasers as well as a recently released 577-nm yellow unit, which can be combined together on the same slit lamp system.
Figure 4. Clinically significant macular edema. The ETDRS concluded that focal coagulation can reduce the risk of moderate vision loss in such patients.
Despite the challenges we face in treating retinal disease, we are optimistic that the future will bring new innovations to help us treat these patients even more effectively. In the second part of this report (later in ), we will share details about next-generation technology we hope and believe will be unveiled in the future. RP
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