A, The ordinary tube uses a low electric field of 1.25 × 107 V/m applied to the target and is able to produce only 1 electron hole pair from a single incident photon. B, The high-gain avalanche rushing–amorphous photoconductor (HARP) tube uses a high electric field of 108 V/m applied to the selenium target, which accelerates electron hole pairs initiated by an incident photon. These accelerated carriers produce another electron hole pair through impact ionization. This multiplication effect occurs in the target to notably increase the sensitivity, and finally, 600 electron hole pairs are produced from a single photon in the HARP tube.
The setup of the high-definition television (HDTV) single-camera system in the operating room. For low-illumination surgery, the camera is switched to the HDTV high-gain avalanche rushing–amorphous photoconductor camera. Although only one viewer's monitor is present in the figure, additional monitors can be set up.
The actual setup of the devices shown in Figure 2. Note the primary surgeon is performing surgery while observing through the stereoscopic high-definition television viewer.
The images of cataract removal and posterior chamber intraocular lens insertion in the pig cadaver eyes for the stereoscopic high-definition television viewer. The photographs have been produced from videotape by the video-capture procedure. A, Continuous curvilinear capsulorhexis is being performed. Note the clear visualization of the cutting edge of continuous curvilinear capsulorhexis (60,600 lux). B, Phacoemulsification and aspiration is being performed (36,000 lux). C, Note the clear visualization of the spider-shape folding intentionally created during polishing of the posterior lens capsule (15,000 lux). D, Insertion of the posterior chamber intraocular lens (4430 lux).
Images of pars plana vitrectomy in the pig cadaver eyes for the high-definition television stereoscopic viewer. The photographs have been produced from videotape by the video capture procedure. A, Removal of the vitreous gel (4500 lux). B, Procedures during "back flash" technique for creating posterior vitreous detachment (14,700 lux). C, Membrane peeling. Note the fine fibrous tissue (8900 lux). D, Membrane peeling. Note the fine fibrous tissue (6300 lux).
Miyake K, Ota I, Miyake S, Tanioka K, Kubota M, Mochizuki R. Application of a Newly Developed, Highly Sensitive Camera and a 3-Dimensional High-Definition Television System in Experimental Ophthalmic Surgeries. Arch Ophthalmol. 1999;117(12):1623–1629. doi:10.1001/archopht.117.12.1623
To apply a new television system, which displays highly sensitive, high-quality 3-dimensional (3-D) images, in performing experimental ophthalmic surgeries.
By combining a high-gain avalanche rushing–amorphous photoconductor (HARP) camera, recently developed in Japan, which has 600 times greater sensitivity than conventional television cameras, and a single-camera, 3-D high-definition television system, which displays high-quality 3-D images, we performed cataract/intraocular lens surgeries and pars plana vitrectomies under various illumination intensities in pig cadaver eyes.
Cataract/intraocular lens surgeries were performed using 7.3% the intensity of ordinary surgical microscopic illumination; vitrectomies were performed using 30.2% the intensity of an ordinary endoillumination probe with the HARP camera and by observing the stereoscopic display of the single-camera 3-D high-definition television system. Images identical to those observed by the surgeon were displayed on the stereoscopic display monitor.
The system not only allowed surgeries to be performed under lower intensities of operating light but also provided real-time, highly sensitive 3-D images identical to those observed by the surgeon; thus, the device may be effectively used for education, team surgery, and telesurgery.
The new television system for ocular surgeries to be performed under lower intensities of operating light as well as providing real-time, highly sensitive 3-D images identical to those observed by the surgeon may be effectively used for education and telesurgery.
THE INTRODUCTION of the operating microscope in different fields of medicine, including ophthalmology, neurosurgery, and otorhinolaryngology, dramatically improved the quality of surgery and led to the development of various new surgical techniques. While the operating microscope has facilitated the development of microsurgery, stereoscopic views are available to a limited number of observers. Although side microscopes and assistant's microscopes have now been made available for assistants and advisors, still only limited numbers of people are permitted to observe the surgical field. For this reason, the side microscopes of today's operating microscopes are equipped with a television (TV) camera. More recently, the camera has been attached to the side microscopes of the right and left optical paths to display stereoscopic views. With the latter method, however, the images are displayed with the ordinary National Television Standards Committee system; hence, the images and their colors are of poor quality, and the amount of information obtained remains insufficient. Furthermore, the system requires 2 sets of cameras, a videotape recorder, and other necessary equipment, and these factors have limited its wider use.
Another disadvantage of microsurgery in ophthalmology is that intense illumination of the operating microscope for anterior segment procedures1- 5 as well as endoillumination for retinal surgeries6- 8 are reported to cause retinal phototoxicity. To minimize this risk of retinal phototoxicity from the operating microscope, surgical time has been extensively shortened,2 the route of illumination has been changed from coaxial to oblique, only a minimum amount of illumination necessary for each procedure is applied, excess use of oxygen is eliminated,7 intraocular lens (IOL) biomaterials are now vastly improved, cooler irrigating solution is applied,9 and various filters are introduced during surgery.10 Despite these strategies, the risk of light toxicity has not been eliminated.
The 2 TV devices recently developed in Japan by the Japan Broadcasting Corporation, Tokyo (ie, Nippon Hoso Kyokai [NHK]), and its groups, the NHK Science and Technical Research Laboratories, have the potential for further reducing the risk of light damage described above. One is a system that transmits 2 separate images from the side microscopes into a high-definition (HD) TV camera through a newly developed optical adapter and provides the primary surgeon as well as the surgical assistant or advisor with high-quality stereoscopic images comparable to those observed through a conventional operating microscope.11 The other is a newly developed TV camera that has 600 times greater sensitivity than ordinary TV cameras.12,13 In this study, the 2 systems have been combined and successfully used to provide realistic images during experimental cataract/IOL surgeries and pars plana vitrectomies in pig cadaver eyes performed under low-intensity operating illumination.
The science and technical research laboratories of the NHK developed a pickup tube called the HARP12,13 that is compatible with an HDTV camera. The tube uses the avalanche multiplication effect in the amorphous selenium target. In the HARP pickup tube, an electron hole pair initiated by an incident photon is accelerated by a high electric field of 108 V/m applied to the target. These accelerated carriers produce another electron hole pair through impact ionization as shown in Figure 1, bottom. This multiplication effect occurs in the target to notably increase the sensitivity. While ordinary tubes (Figure 1, top) use a low electric field of 1.25 × 107 V/m, they are able to produce only 1 electron hole pair from a single incident photon. With the HARP tube, 600 electron hole pairs are produced from a single photon: the HARP tube has 600 times greater sensitivity than ordinary tubes. When converted to sensitivity classifications of the American Standards Association and the International Standards Association, the sensitivity of ordinary tubes is about 80 while that of the HARP tube is approximately 50,000.
Conventional 3-D TV systems require a camera to be attached to the right and left side microscopes of an operating microscope, and these right and left images are displayed onto a screen via 2 separate projectors. A pair of 3-D glasses, which deflects the images back to the original ones and allows the right eye to pick up the right images and the left eye the left images, must be worn by all the viewers. The major drawback of these systems is that they all require 2 sets of related equipment, including the camera, videotape recorder, and cable line.
The system introduced here, known as a single-camera 3-D HDTV system (Figure 2),11 has successfully solved the problems stated above by using an optical lens adapter connected to the HDTV camera and an optical adapter connected to the HDTV stereoscopic viewer. The optical lens adapter combines 2 images, 1 for the right eye and 1 for the left, to the HDTV camera through a prism, an image rotator, and a lens. The optical adapter, combined with a prism and a lens, has the ability to pick up right and left images and display them as stereoscopic images. The viewers need not wear special glasses.
Figure 2 and Figure 3 show the setup of these instruments in the operating room. To perform surgeries under lower illumination, the HDTV camera shown in Figure 2 was switched to the HDTV-HARP camera. Although only one viewer's monitor is shown in Figure 2, in addition to the surgeon's HDTV stereoscopic viewer, the monitor's viewers can be set up as necessary at distant regions to observe the procedure. Figure 3 demonstrates no considerable differences in ergonomics for the primary surgeon, such as in working distance compared with a conventional operating microscope. For assisting staff, adequate minor modification is necessary and is quite possible.
To simultaneously compare the same surgical field, a conventional National Television Standards Committee camera (3-charge coupled-device [3CCD] camera; Hitachi, Tokyo) was attached to either the right or left side microscope of an operating microscope and an HD-HARP camera (Figure 1, bottom) was attached to the remaining side microscope. The 2 cameras differ in their iris function. For this study, the iris of the 3CCD camera was completely opened while that of the HD-HARP camera was adjusted automatically.
Experimental cataract/IOL surgeries or vitrectomies were performed in pig cadaver eyes under 7 different intensities of light listed in Table 1 and Table 2. More specifically, for cataract/IOL surgeries, the intensity of the Zeiss OPMI (Carl Zeiss Ltd, Oberkochen, Germany) operating microscope was set at 7 different illuminations starting from vol 4 (maximum) to vol 0.2 (minimum); for vitrectomies, the intensity of the fiberoptic probe was set at 7 different voltages starting from 12 V (maximum) to 5 V (minimum). Intensities of illumination of the surgical fields were directly measured by means of the digital illumination meter (Minolta, Tokyo). Both surgical procedures were performed by the primary surgeon (I. O.) and there were 2 observers (K. M. and S. M.) who evaluated each intensity by determining whether it allowed adequate visualization to complete the surgery. All images were recorded using a videotape recorder for either the HDTV or National Television Standards Committee system.
Using the single-camera 3-D HDTV system shown in Figure 2 and Figure 3, cataract/IOL surgeries or vitrectomies were performed in pig cadaver eyes. For the former, the illumination intensity of the Zeiss OPMI operating microscope was set from vol 2 to vol 0.5; for the latter, the intensity was set from 12 V to 8 V.
Three consecutive eyes underwent cataract surgeries by achieving continuous curvilinear capsulorrhexis followed by phacoemulsification and posterior chamber IOL implantation under the several intensities of illumination. Vitrectomies were achieved by removal of the vitreous, membrane peeling, and retinotomy using ordinary contact lenses, again under the several intensities of illumination. The primary surgeon determined whether the HDTV stereoscopic viewer at each illumination intensity provided sufficient visualization to continue with the surgery, and the observers evaluated the quality of the images displayed and the incidence of eyestrain. All images were recorded using a videotape recorder for an HDTV system.
The results are summarized in Table 1. We were able to clearly observe the surgical field using the 3CCD camera under vol 4 (100,000 lux) of the operating microscope, but when the HD-HARP camera was employed, this intensity was too bright and interfered with clear visualization. Both cameras under vol 2 (60,300 lux) allowed adequate observation (36,300 lux). With the HD-HARP camera, better visualization was achieved under vol 1 but not with the 3CCD camera. Moreover, the HD-HARP camera under vol 0.8 (15,300 lux) to vol 0.3 (1080 lux) permitted observation, but, again, not the 3CCD camera. The visualization was insufficient with the HD-HARP camera under vol 0.2 (460 lux). Evaluation by the primary surgeon and 2 observers found that the HD-HARP camera allowed cataract/IOL surgeries to be performed using 4430 lux of the amount of surgical microscopic light while the 3CCD camera allowed surgeries using 60,600 lux (Table 1). This means cataract/IOL surgeries were performed using 7.3% the intensity of ordinary surgical microscopic illumination with the HARP camera.
The results are summarized in Table 2. Both cameras provided sufficient visualization under 12 V (14,600 lux). The HD-HARP camera allowed sufficient observation under 10 V (8940 lux) but not the 3CCD camera. Moreover, the HD-HARP camera under 9 V (6300 lux) led to excellent visualization, while 8 V (4400 lux) and 7 V (2800 lux) led to sufficient observation but not with the 3CCD camera. With the HD-HARP camera, 6 V (1640 lux) resulted in a shot noise owing to a fluctuation of incident photons, diminishing the quality of the images, and 5 V (820 lux) could not provide useful visualization. A wider visual field was obtained with the HD-HARP camera under all illumination intensities. Evaluation by the primary surgeon and 2 observers found that the HD-HARP camera allowed vitrectomies to be performed using 4440 lux of the fiberoptic probe light while the 3CCD camera allowed it using 14,700 lux (Table 2). This means vitrectomies were performed using 30.2% the intensity of an ordinary fiberoptic probe light with the HD-HARP camera.
Under the several intensities of surgical microscopic illumination and by observing the images through the HDTV stereoscopic viewer, the same surgeon performed surgery in 3 consecutive cases but did not experience any eyestrain. The system also provided high-quality 3-D images of the surgical procedure. Figure 4 shows the images of continuous curvilinear capsulorrhexis, phacoemulsification, the posterior lens capsule, and IOL insertion (parts A, B, C, and D, respectively). The 2 other surgeons observing the surgery on the monitor of the stereoscopic viewer, which provided excellent 3-D images, also did not experience eyestrain. Decreasing the volume to 0.5 (4430 lux) did not affect the results, and continued to allow the surgeon to perform the procedure and the 2 observers to observe.
Under the several intensities of fiberoptic probe lights and by observing the images through the stereoscopic viewer, the same surgeon performed vitrectomies in 3 consecutive cases but did not experience any eyestrain. Figure 5 shows the images of removing the vitreous, creating posterior vitreous detachment (parts A and B, respectively), and membrane peeling (parts C and D). The 2 other surgeons observing the surgery on the monitor of the stereoscopic viewer, which provided excellent 3-D images, also did not experience eyestrain. Decreasing to 8 V (4440 lux) did not affect the results and continued to allow the surgeon to perform the procedure and the 2 observers to observe.
In this study, 2 TV devices recently developed in Japan were used in experimental ophthalmic surgeries. One is called the HARP camera, which has approximately 600 times greater sensitivity than ordinary TV cameras and allowed ophthalmic surgeries to be performed under much less intensity of light than in ordinary microscopic surgeries. The other device, a single-camera, 3-D HDTV system, was used to display high-quality stereoscopic views of the surgical field.
The present experimental study revealed that cataract/IOL surgeries could be performed using 7.3% and vitrectomies 30.2% the intensity of ordinary surgical microscopic illumination or fiberoptic probe light when the HARP camera was introduced. Additionally, the HARP camera provided a wider surgical field than ordinary cameras. Long-term results indicate that retinal phototoxicity from the operating microscope is most severe in cases having undergone vitreoretinal surgeries.8 The indications for vitrectomy today include a wide range of disorders, among them various macular diseases. Compared with normal maculae, the diseased maculae are probably more susceptible to light-induced damage.8 Applying a lower intensity of illumination of the operating microscope or fiberoptic probe light has been the most effective method for minimizing retinal phototoxicity. Hence, the HARP camera permitting surgeries to be performed under lower intensity is indeed advantageous in ophthalmic surgeries.
The single-camera 3-D HDTV system provided high-quality images without any difference in the focal distance, size, and color between right and left images. However, the most notable advantage of the system was that its stereoscopic monitor permitted the assistants, nurses, students, and others in the operating room to observe identical images seen by the surgeon without the need for special glasses. Connecting the HARP camera to this system resulted in surgeries performed under lower intensities of light. Furthermore, the single-camera 3-D HDTV system may also have the following merits: (1) team surgery may be accomplished since all of those present in the operating room observe identical stereoscopic images of the surgical field, (2) the images can be transmitted to experts in distant regions for timely advice and support, (3) the system may be used for educational purposes by creating a database with 3-D images of surgeries performed by experts on typical ophthalmic cases, and (4) the system can lead to the introduction of a new superimposed navigation system14 by incorporating related information onto the images obtained. The superimposed navigation system has already been developed for phacoemulsification and vitrectomy procedures, which indicates to the surgeon the most adequate settings of phacoemulsification and vitrectomy machines; a similar system is expected to be introduced and effective for other simple procedures, such as laser refractive surgeries that can be system guided.
The application of the highly sensitive, high-quality 3-D TV system introduced here is not limited to the operating room; it can also be used in conjunction with a slitlamp microscope and other optical devices in the outpatient section. As was accomplished in the operating room, such applications will allow everyone on the team to observe identical, high-quality stereoscopic images that may be used for educational purposes and allow the creation of a database of various test findings. There are only slight differences between the new 3-D TV system and the conventional one in terms of ergonomics. Even if there are, they can be easily resolved. Furthermore, telemedicine, used to extend health care to people living in sparsely populated regions, is made possible only with such advanced technologies in telecommunication.15- 17 We believe the 3-D TV system discussed here may considerably contribute to achieving this goal. The availability of such a system will allow an expert to provide timely and appropriate methods of treatment without having to physically travel to these remote areas, thus reducing the cost of medicine, which is one of the goals of telemedicine.15
The 3-D TV system, however, requires refinements, one of which is to reduce the size and the weight of the HARP camera for easier handling in the operating room. We also need to investigate the possibility of the monitor leading to eyestrain and determine a length of time for which it may be safely observed by those on the surgical and outpatient team. Moreover, this system is still a prototype and very expensive. Mass production of the system at a reasonable cost will need to be addressed.
Accepted for publication August 30, 1999.
Reprints: Kensaku Miyake, MD, Shohzankai Medical Foundation, Miyake Eye Hospital, 1070-Kami 5S, Higashiozone-cho, Kita-ku, Nagoya, 462-0823, Japan (e-mail: firstname.lastname@example.org).