40.3.1 Visualization

Vitreoretinal surgery is always performed with an operating microscope. Historically, the lenses used for vitrectomy were planoconcave or biconcave lenses, which allow a limited field of view (20–35 degrees). ¹ Prism lenses were also used to increase the field of view to 60 degrees. ² The retinal periphery was difficult to visualize with these viewing systems, making the surgery technically cumbersome. Wide-angle viewing systems were developed that revolutionized vitreoretinal surgery as surgeons gained access to the peripheral vitreous and retina where substantial vitreoretinal pathology is often present. These systems are based on the principles of binocular indirect ophthalmoscopy and require an image inverter mounted on the operating microscope. Two types of wide-angle viewing systems for vitrectomy surgery exist: contact and noncontact systems. Contact systems (Volk Reinverting Operating Lens System, Volk; AVI Panoramic Wide-Angle Viewing System, AVI) provide 10 degrees greater field of view than noncontact systems and eliminate corneal aberrations. However, surgeons are dependent on a skilled assistant. The most popular noncontact systems are the Binocular Indirect Ophthalmomicroscope (BIOM) by Oculus and the Resight 700 system incorporated in the Lumera operating microscope by Zeiss. Noncontact systems require greater ocular rotation for viewing the periphery than contact systems. Surgeons switching from contact systems to noncontact systems are faced with a steep learning curve. The field of view with the BIOM depends primarily on the distance between the noncontact lens surface of the operating microscope and the corneal surface. As the noncontact lens approaches the cornea, the observed field becomes wider. Also, focusing the operating microscope sharpens the image. Focusing the BIOM can be complicated for beginners due to difficulty in maintaining a suitable distance between the indirect lens and the corneal surface and in maintaining the optimal distance between the height of the operating microscope and the corneal surface. However, once the surgeon becomes accustomed to the BIOM system, most vitreoretinal procedures can be performed safely and efficiently. More recently, another noncontact system, the Resight 700, was introduced by Zeiss and is becoming increasingly popular. It has a unique focusing system that allows the reduction lens set to be moved automatically inside the operating microscope. That allows the surgeon to obtain a high-resolution wide-angle view of the retina. Most surgeons perform macular surgery with a plano contact lens which provides high magnification and good lateral and axial resolution and other vitreoretinal procedures with the BIOM or Resight system Image.

40.3.2 Illumination

The current method of endoillumination, using a fiberoptic probe inserted into the vitreous cavity, was first introduced in the 1970s for 20-gauge vitrectomy. ³ In the 20-gauge era, illumination was made possible with a halogen bulb. However, when using a small-gauge fiberoptic probe with a conventional halogen light source, only 50% or less of the brightness found with the 20-gauge system is obtained. To compensate, xenon and mercury vapor bulbs were introduced. These systems provide superior illumination even with 25- or 27-gauge systems. Concerns regarding phototoxicity have been raised with these powerful illuminating systems, especially when the endoilluminator is close to the retina for a prolonged period of time. ⁴ More recently, wide-angle illumination probes were introduced ⁵ that provide a field of view close to 100 degrees compared to the standard 50 or 80 degree field of view that focal probes produce. A chandelier illumination system, which permits the surgeon to perform bimanual maneuvers, may also be used. The retina can tolerate this type of endoillumination for a prolonged period of time without evidence of toxicity compared to the conventional endoilluminator (Fig. 40-2).

40.3.3 Chromovitrectomy

The term “chromovitrectomy” refers to the use of vital dyes during vitreoretinal surgery to assist with the identification of preretinal tissues and membranes. ⁶ It was first introduced by Kadonosono in 2000 when he used indocyanine green (ICG) to stain the internal limiting membrane (ILM) in macular hole surgery. ⁷ ICG binds to ILM, thus facilitating ILM visualization and aiding in its removal. It has also been proposed for visualization of ERM. There are concerns, however, as some investigators have reported suspected toxicity. ⁸ Other vital dyes used for ILM peeling are trypan blue and brilliant blue. Triamcinolone acetonide is superior in staining the vitreous and the posterior hyaloid but is not as good as ICG, trypan blue, or brilliant blue for ILM staining. Triamcinolone acetonide is used commonly by many surgeons to visualize the vitreous and ensure removal of the entire posterior vitreous cortex during surgery.

40.3.4 Cannula-Trocar Systems

Historically, 20-gauge surgery was performed for all pars plana vitrectomies; however, during the last decade, there has been a shift to transconjunctival MIVS with cannulated sclerotomies. In 2002, Fujii et al ⁹ introduced the 25-gauge transconjunctival sutureless vitrectomy system. The 25-gauge vitrectomy creates a smaller, self-sealing incision 0.55 mm in diameter, approximately half the size of the 1.15-mm incision created during 20-gauge vitrectomy. Initially, there were limitations with the 25-gauge instruments given their high flexibility and increased fragility. Eckardt introduced the 23-gauge system in 2005 ¹⁰ with an incision size of 0.72 mm in diameter (Fig. 40-3), and in 2010, Oshima et al introduced the 27-gauge system ¹¹ with an incision size of 0.4 mm. The initial limitations with the early vitrectomy probes were later overcome as new stiffer probes were designed. Advantages of modern MIVS include less conjunctival disruption and faster surface recovery with less postoperative discomfort, quick entry and exit from the eye, lower incidence of entry site–associated retinal breaks, lower flow rates and possibly less retinal traction, smaller cutter port size and closer proximity to the probe tip with more precise end cutting ability, and valved cannulas that eliminate sclerotomy leakage. Currently, the majority of vitreoretinal procedures are performed with 23- or 25-gauge transconjunctival cannula-trocar–based systems; 20-gauge systems are typically reserved for some trauma cases or in cases with an IOFB. Three sclerotomies are created for vitrectomy through the pars plana, 3.5 to 4.0 mm posterior to the limbus in phakic eyes and 3.0 to 3.5 mm posterior to the limbus in pseudophakic or aphakic eyes (Fig. 40-4). One sclerotomy is placed inferotemporally and provides continuous infusion of a saline solution. Two additional sclerotomies are placed (superonasally and superotemporally) and provide access for the endoilluminator and the vitreous cutter. Many surgeons prefer to displace the conjunctiva before the trocar insertion. Conjunctival displacement is essential for the transconjunctival sutureless technique, to provide containment of a vitreous wick as well as to prevent access of the tear film to the sclerotomies, thereby potentially reducing the endophthalmitis risk. In addition, the majority of surgeons prefer to enter the globe in a two-plane approach. The initial insertion is approximately 30 degrees relative to the sclera and the second trajectory is perpendicular to the sclera. This results in the creation of more stable and watertight wounds. After cannula placement, it is very important to confirm with direct visualization that the infusion cannula tip is in the vitreous cavity before the infusion is turned on, thus avoiding the possibility of infusing into the suprachoroidal space.

40.3.5 Vitrectomy Systems

Machemer introduced the vitreous infusion suction cutter in 1970. ¹² The original instrumentation was 17 gauge with an external diameter of 1.5 mm. Douvas developed the rotoextractor in the early 1970s, ¹³ and subsequently, O’Malley and Heintz introduced the Berkley Bioengineering Ocutome 800, a 20-gauge vitrectomy probe with a 0.9-mm external diameter and 0.47-mm internal diameter. ¹⁴ This was the first lightweight pneumatic probe with surgeon foot pedal–controlled on-off aspiration. Over the ensuing years, several additional vitrectomy probes were developed, and in the mid-1990s, Alcon developed the first integrated vitrectomy system, the Accurus. This included an advanced graphical user interface with soft keys, vented gas-forced infusion, integrated fragmatome, silicone oil injector, and a halogen light source. The Accurus could provide cutting speeds of up to 2,500 cuts per minute. A similar system, the Millenium Microsurgical System, was developed by Bausch & Lomb. For almost 30 years, 20-gauge vitrectomy surgery was the standard until MIVS was introduced in the early 2000s. The Accurus was later substituted with the Constellation vitrectomy system, which provided cutting speeds of up to 7,500 cuts per minute. Similarly, the Millennium was substituted with the Stellaris PC. Higher cutting speeds are considered preferable because there is less retinal traction as the vitreous is cut. In addition to increasing safety by decreasing retinal traction and mobility, increased cut rates may also increase efficiency by enhancing flow through the cutter. An integral component contributing to the dynamics of vitreous flow into the cutter is the duty cycle. Duty cycle is defined as the proportion of time the port stays open during the entire length of the open-close cycle. Modern vitrectomy machines such as the Constellation vitrectomy system allow the surgeon to control the duty cycle.

40.3.6 Lensectomy

Pars plana lensectomy is performed (Fig. 40-5) when there is a cataract precluding adequate visualization of the fundus or when the crystalline lens is subluxated or dislocated. In some cases, the capsular bag can be retained for simultaneous or possible future IOL implantation; however, removal of the lens and the entire capsule is recommended in cases of significant trauma and/or anterior proliferative vitreoretinopathy (PVR). If the crystalline lens and/or the capsule are retained in eyes with advanced anterior PVR, the capsule may serve as a scaffold for the proliferation of membranes, possibly resulting in recurrent retinal detachment and hypotony. In the pre-MIVS era, a 20-gauge fragmatome (sleeveless straight ultrasonic probe) was used for removal of the lens nucleus and cortex. However, with the advent of MIVS, many surgeons utilize the 23-gauge cutter to remove the lens. If the lens nucleus is exceptionally hard, it can be removed with the fragmatome, which requires enlargement of the 23-gauge wound. When using the fragmatome, the surgeon should be careful not to engage any vitreous in the tip of the probe as it will result in vitreous traction. Almost all cases of lensectomy are performed with a pars plana infusion. If there is a white cataract with no visualization posteriorly, an anterior chamber maintainer can be placed until there is sufficient view to visualize the pars plana infusion cannula tip so that the infusion fluid can be turned on safely. If an IOL is placed, a silicone IOL should be avoided in cases that may require future silicone oil tamponade.

40.3.7 Vitrectomy

Briefly, vitrectomy consists of first removing the vitreous around the sclerotomies, followed by removal of the core vitreous, induction of a PVD if it is not already present, peripheral vitreous shaving, and removal of any ERM. All steps of the vitrectomy should be performed under direct visualization. The vitreous cutter is placed through the superotemporal sclerotomy to perform the initial portion of the vitrectomy as access through the superotemporal sclerotomy provides a greater range of motion for the vitreous cutter. In phakic eyes, the nasal vitreous can be accessed by placing the cutter through the superonasal sclerotomy, thus minimizing the risk of traumatizing the crystalline lens. It is important to remove the vitreous near the sclerotomies before proceeding to the subsequent steps as it minimizes the chances of iatrogenic retinal breaks close to the sclerotomies.

40.3.8 Epiretinal Membrane Dissection

The first steps are to remove the vitreous around the sclerotomies, perform a core vitrectomy, and then induce a PVD if it is not already present. Most cases of idiopathic ERM are associated with a PVD, but if a PVD is not present, then a soft silicone tip or the vitreous cutter is used to create a PVD by using high aspiration adjacent to the optic nerve. Once the posterior hyaloid is engaged, it can be elevated and stripped to the periphery by gently moving the silicone tip or the cutter anteriorly. In some eyes with a strongly adherent posterior hyaloid, a pick or microvitreoretinal (MVR) blade can be used to initiate this process.

Machemer performed ERM peeling shortly after he developed vitrectomy. ¹⁵ He used a 23-gauge bent needle to engage and lift the ERM. Subsequently, O’Malley introduced the pick, a rounded-tip instrument, and Steve Charles developed end-grasping forceps (Fig. 40-6). Most surgeons nowadays prefer to use forceps to peel the ERM, while some prefer to do this after the ERM has been stained with one of the dyes discussed previously. If an ERM edge cannot be identified, then a pick, an MVR blade, or a diamond-dusted scraper introduced by Tano can be used to develop an edge. Some surgeons have suggested peeling the ILM in all cases of ERM removal in order to minimize the risk of ERM recurrence; however, this remains controversial.

In cases of proliferative diabetic retinopathy with traction retinal detachment (TRD), different techniques are utilized in order to relieve traction on the macula. In these cases, the surgical goal is to relieve anterior-posterior and tangential traction of the posterior hyaloid and ERM. The techniques commonly used are segmentation, delamination, and en-bloc dissection. Segmentation involves the vertical cutting of ERM between epicenters (individual neovascular connections from the retina to the membrane) into small segments (Fig. 40-7). Delamination (Fig. 40-8) involves removal of fibrovascular tissue from the retina using horizontal scissors to sever the individual neovascular connections from the retinal surface. Segmentation or delamination can be performed with either specially designed vertical (Fig. 40-9) or horizontal scissors, curved scissors, or even with the vitreous cutter probe. In en-bloc delamination, a small window in the partially detached posterior hyaloid is made so that a horizontal scissors can be introduced into the retrohyaloid space. Gentle traction from the vitreous immobilizes the fibrovascular membrane, and exposes areas of adhesion between the membrane and the retina, which facilitates membrane excision. The endoilluminator or illuminated forceps can be used to facilitate the dissection. When the membranes have been completely separated from the retina, the remaining posterior hyaloid complex can be removed with the vitreous cutter. Current MIVS cutters have the port close to the tip, which makes segmentation and delamination safer. Alternatively, one may use scissors to segment and forceps to dissect. Viscoelastic devices can be also used to create a plane for dissection and protect the retinal surface. In cases of strongly adherent membranes, bimanual techniques are often used with a lighted pick and forceps or a chandelier, scissors, and forceps.

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