Choroidal neovascularization (CNV) is the main cause of vison loss in individuals with age-related macular degeneration (AMD), occurring in 18% of patients over 5 years.1,2 A tool that was once mainly used by glaucoma specialists is finding a new purpose in the hands of vitreoretinal surgeons. First widely utilized in endoscopic cyclophotocoagulation treatment for the management of open- and narrow-angle glaucoma, vitreoretinal surgeons have found that endoscopic visualization allows them to view the posterior segment of the eye in ways not possible with standard vitrectomy techniques.

Because of this enhanced visualization, previously unthinkable surgical interventions have now become feasible. Eyes with certain types of advanced disease deemed nonoperable in the past have a chance at successful anatomic rehabilitation with endoscopic-assisted surgery. Some eyes with operable diseases can achieve equivalent or perhaps improved anatomic outcomes with more efficient, faster, less aggressive, and less inflammogenic surgical techniques using the endoscope.

PRODUCT SPECIFICATIONS
The word endoscope stems from the Greek words endo scopos, meaning to look within. The machine is a fiberoptic-based instrument used in a wide variety of medical and nonmedical applications. It has become a key tool in modern microincisional and minimally invasive diagnostic and therapeutic modalities.

The ophthalmic endoscope created by Endo Optics (Little Silver, NJ) has a 20-gauge rigid design incorporating three fiber bundles, which allow simultaneous illumination, visualization, and application of laser. An unfiltered 175-W xenon lamp serves as the light source and can be modulated in 256 discrete steps by a foot pedal. Light travels down a 75- to 100-fiber illumination bundle delivering 2,700 lumens at the distal end of the endoscope at a color temperature of 5,800° K. The integrated laser is also foot-pedal activated and consists of a 640-nm diode aiming laser and 810-nm diode treatment laser capable of generating pulse lengths of 50 to 2,000 milliseconds and 0 to 1200 mW of power. Laser energy travels down a single 200-µfm laser fiber.

The imaging fiber bundle is 600 µm in diameter and is composed of 10,000 fibers arranged in a circular pattern—10,000 fibers is equivalent to 10,000 pixels as compared with the 307,200 pixels found on a standard 480 X 640 video screen. An internally mounted single-chip Toshiba (Tokyo) video camera images the proximal end of the imaging fiber bundle and generates a 480i video signal. The endoscope has an insufficient number of fibers to warrant higher-definition video-imaging formats (ie, 480p, 720p, 1080i, 1080p).

ENDOSCOPE APPLICATIONS
Vitreoretinal surgery is all about visualization. You cannot fix what you cannot see. Additionally, you cannot fix something well if you do not see it clearly. The endoscope is a useful adjunct for retinal surgery in the following three scenarios: (1) bypassing media opacity, (2) specialized viewing angles, and (3) facilitating less-invasive surgical techniques.

  1. The ability to visualize and operate on the posterior segment in the setting of severe anterior-segmentÐbased media opacity is the most immediately useful of the endoscope features. I have found the endoscope useful in many situations, including an acute macular-sparing retinal detachment following penetrating keratoplasty where the corneal graft had not yet cleared. I also used it in a patient with acute postoperative endophthalmitis with an opaque cornea due to Serratia species and light perception vision and in tractional retinal detachment due to aniridic anterior fibrosis syndrome in the setting of aniridic keratopathy. Other examples include an aphakic patient with a posteriorly dislocated endothelial keratoplasty button, an epiretinal membrane in a patient with a 1.5-mm functional pupil from capsular bag contracture after placement of 50 series Morcher artificial iris segments (Morcher GmbH, Stuttgart, Germany) following trauma, and retinal detachment in the setting of a Boston keratoprosthesis (Massachusetts Eye & Ear Infirmary).

  2. Endoscopic surgical visualization during vitreoretinal surgery provides a unique inside-out view of ocular anatomy (figures 1 and 2). There are certain instances in which these special viewing angles become invaluable in achieving precise surgical anatomic results. When suturing a secondary posterior chamber intraocular lens (IOL) in the setting of distorted anatomy after penetrating globe injury, it is reassuring to directly visualize the ciliary sulcus and know the precise anatomy of the area in which you are planning to place the IOL fixation sutures. It also precisely confirms IOL position. Sometimes, a gentle nudge will take an IOL haptic off the ciliary body and put it in the ciliary sulcus.

    Endoscopic visualization may also greatly facilitate dissection of extreme anterior grade C-4 and C-5 proliferative vitreoretinopathy (PVR) (Figure 3). In cases of subretinal migration of perfluoro-n-octane or silicone oil, excellent direct visualization of the subretinal space is achieved by advancing the endoscope through a retinal break. This visualization allows complete, efficient, and atraumatic removal of the subretinal bubble. Direct endoscopic visualization of the subretinal space also facilitates dissection of subretinal PVR in some instances.

  3. Patients with advanced posterior segment pathology often require a meticulous and complete vitrectomy in addition to surgical dissections that involve the entire realm of the posterior segment. Many times, visualization is accomplished by means of careful intraoperative scleral depression. In patients with peripheral corneal disease, severe Soemmering's ring, previous trauma, previous pupilloplasty, or correctopia, the reduced functional pupillary diameter obligates increasingly aggressive scleral depression. In severe cases, this may not be feasible or is ill advised. The endoscope, however, can allow visualization in these cases as well as in eyes where aggressive scleral depression is optically possible but not preferred (eg, penetrating keratoplasty, marginally stable IOL, conjunctival filtering bleb, recent trauma, multiple retinal detachment repair, hypotony, and ischemic diabetic or other retinopathy). Endoscopic visualization may also allow for less-invasive and less-complex surgeries, obviating the need to place a temporary keratoprosthesis, or avoiding the explantation of a marred silicone IOL. Surgical time is reduced, less inflammation is created, and the need for a second surgeon may possibly be avoided.

SURGERY
My first experience with the endoscope was associated with more than a bit of anxiety. The beautiful stereo 3-D cues that I was used to receiving from the stereo operating microscope were replaced by a much grainier 2-D image from the endoscope displayed on a video monitor, located a face turn away from the patient. Furthermore, the illumination source and viewing aperture are the same (ie, the tip of the endoscope), so the shadows generated during standard vitrectomy surgery—which are a monocular 2-D indication of depth—are also gone. Nonetheless, other monocular cues are available and can be assimilated with practice and patience. Moving the endoscope tip close to your target results in breathtaking magnification that compensates somewhat for the grainy 10,000-pixel image.

When using the endoscope, the lighting level must be adjusted for distance. High illumination is needed to view objects that are far out, while low illumination eliminates video whiteout and works best for close maneuvers. The microscope light provides global external transillumination, which can prove either useful or detrimental at various points throughout surgery.

MOVES LIKE VITRECTOMY INSTRUMENTS
The endoscope moves three-dimensionally inside the eye like any other vitrectomy instrument. In addition to the X-Y-Z position of the instrument in the eye, however, two additional variables need to be considered when the viewing aperture is at the tip of the endoscope. These are torsion and the vector from the endoscope sclerotomy port to the endoscope tip; both greatly have an impact your viewing vantage point. Curved and straight endoscopy probes are available. The straight probe is the most intuitive to use, but the curved is a bit easier on the hands and wrists when performing a lot of very anterior dissection.

When starting out, it is most helpful to hold the endoscope in the hand you would usually hold the light pipe. From this vantage point, the view posteriorly is the most intuitive and is very familiar to the surgeon. This is a good starting-off point. When looking inferiorly, the view is still rather intuitive; however, when working superiorly, everything appears backward, which may prove challenging to the novice.

THE LEARNING CURVE
I recommend learning this technique on a cadaver eye. Once you are familiar with the basics of endoscopic vitrectomy surgery, you can use the endoscope as a light pipe during normal vitrectomy cases, increasingly glance away from the microscope to the video feed from the endoscope, and use the endoscope to help visualize cases. You should wait to perform purely endoscopic surgery until you can ensure three points: (1) that you are facile at safely visualizing the entire posterior segment at a distance and up close, (2) that you can maintain positive control and awareness of the endoscope's position in the eye at all times, and (3) that you can visualize and purposefully move the instruments in the contralateral nonendoscopic hand throughout the posterior pole.

Once these skills have been mastered, vitreoretinal surgeons will see the ophthalmic endoscope open up a world of possibility in their surgical armamentarium.

Christopher D. Riemann, MD, is a vitreoretinal surgeon in private practice at the Cincinnati Eye Institute, and he is volunteer faculty for the Department of Ophthalmology at the University of Cincinnati in Ohio. He states that he has no financial interest in the products or companies mentioned. Dr. Riemann may be reached at criemann@cincinnatieye.com; or phone: 513-984-5133.