Chapter 104 – Vitrectomy
In the 30 years since its genesis, remarkable advances in vitreous surgery have established this microsurgical procedure as the most common intraocular operation after cataract extraction. Progress in two major areas fueled the extraordinarily rapid growth in vitreous surgical techniques:
• Understanding of the pathoanatomical changes that affect the retina;
• Introduction of new technology and instrumentation.
In the early years, vitrectomy was used to restore ambulatory vision in eyes that were destined to become blind. Both removal of opacified vitreous and removal of fibrovascular tissue in diabetic retinopathy often resulted in restoration of functional vision. Eyes that had complicated retinal detachments, such as those associated with proliferative vitreoretinopathy or that resulted from severe penetrating injury, were regarded as inoperable previously. As refinements in technique continued and the safety of the procedure was established, the focus shifted to newer applications (e.g., macular surgery). The goals of this surgery are to restore central visual function in such conditions as macular pucker, macular hole, and choroidal neovascularization.
Until the 1960s, it was believed dogmatically that the vitreous body should not be violated deliberately. In 1970, Machemer and Parel introduced the first instrument to cut and remove vitreous, and the first planned vitrectomy procedure was performed in a diabetic patient who had a long-standing vitreous hemorrhage.
PREOPERATIVE EVALUATION AND DIAGNOSTIC APPROACH
The preoperative evaluation of patients who are to undergo vitrectomy includes a careful examination of the clinical situation as well as assessment of the patient’s medical status and anesthetic risk. The surgeon and surgical team review the goals of the planned procedure with the patient and explain the potential benefits and risks.
Slit-lamp examination is carried out to evaluate the anterior segment structures; indirect biomicroscopy is used to determine the vitreoretinal relationships. When a gas bubble tamponade is to be used, the depth of the anterior chamber is examined to assess the possibility of postoperative angle-closure glaucoma. The cornea, size of the dilated pupil, and clarity of the lens are noted to ensure that, intraoperatively, the retina can be visualized adequately. In pseudophakic eyes, the type of intraocular lens (IOL) and its composition are studied. As a consequence of its hydrophobic properties, a silicone IOL may develop condensation on its surface during fluid-air exchange, and the placement of silicone oil intravitreally may result in adhesion of oil droplets to the implant surface, which adversely affects the clarity of the optical zone. Gonioscopic evaluation is carried out in diabetic patients and those who have inflammatory conditions.
The status of the vitreous is best studied using indirect biomicroscopy—a 78D or 90D lens may be used. The absence or presence of separation of the posterior hyaloid surface is determined first, as this finding is critical to the surgical approach in macular conditions. These findings are supplemented by those of careful indirect ophthalmoscopy, which provides information about the severity of epiretinal membrane proliferation, the location of retinal breaks, and anatomical changes in vitreous base and peripheral retinal structures.
In cases of media opacity, ultrasonographic evaluation provides an accurate map of the vitreoretinal relationships. In particular, the mobility of retinal detachment, delineation of tractional regions, and localization of vitreous or subretinal hemorrhage may be depicted. The location and dimensions of prior scleral buckling elements may be determined. In traumatic situations, ancillary tests using computed tomography or orbital radiographic analysis may be necessary to aid in the localization of foreign bodies and damage to periocular structures.
INDICATIONS AND ALTERNATIVES TO SURGERY
The surgical indications for vitrectomy are given in Box 104-1 . These include a wide range of conditions, some of which involve the vitreous or retina focally, whereas others represent more diffuse processes. Other chapters in this book describe the alternative medical approaches for many of the listed conditions.
The majority of vitrectomies are carried out under local, infiltrative anesthetic (retrobulbar block, peribulbar block, or subconjunctival irrigation) with monitored anesthetic care. In instances of extreme patient apprehension or an inability to cooperate, general anesthetic is required. When using general anesthetic and intraoperative gas, it is important to discontinue inhalation of nitrous oxide at least 20 minutes prior to the final injection of gas. Otherwise, elevated intraocular pressure or an inadequate gas fill may result.
A three-port (sclerotomy) vitrectomy is the routine approach, using separate 20-gauge incisions through the pars plana. The incisions are usually located 3.5–4.0?mm posterior to the limbus in phakic eyes and approximately 0.5?mm more anteriorly in aphakic or pseudophakic eyes. An infusion cannula is sutured to the sclera, typically inferotemporally, to allow saline to replace the excised tissue and thereby maintain the intraocular pressure. The two additional sclerotomies allow instrumentation to be placed—usually, one of the instruments is connected to a light source for endoillumination. Such an approach allows bimanual control of eye movement and the use of two hands to engage tissue. The surgical incisions may vary depending on the clinical situation.
In general, a surgical microscope is used to view the fundus during surgery. A planoconcave contact lens is used most commonly,
Indications for Vitrectomy
Nonclearing or repeated vitreous hemorrhage
Traction retinal detachment
Combined traction and rhegmatogenous retinal detachment
Progressive fibrovascular proliferation
Macular distortion by fibrovascular proliferation
Macular edema that results from a taut posterior hyaloid
Retinal detachment with proliferative vitreoretinopathy
Giant retinal tears
Retinal detachment with posterior retinal breaks
Selected primary retinal detachments
COMPLICATIONS OF ANTERIOR SEGMENT SURGERY
Dislocated lens fragments
Dislocated intraocular lens
Aphakic or pseudophakic cystoid macular edema
Anesthetic needle perforation
Traumatic cataract or dislocated lens
Posterior penetration injuries with vitreous hemorrhage and/or retinal detachment
Reactive intraocular foreign body
Subretinal membranes or hemorrhage
Traumatic macular holes
Massive subretinal hemorrhage
Vitreomacular traction syndrome
Serous retinal detachment secondary to optic pit
Transplantation of retinal photoreceptors or retinal pigment epithelium
PEDIATRIC RETINAL DISORDERS
Retinopathy of prematurity
Persistent hyperplastic primary vitreous
Familial exudative vitreoretinopathy
Giant retinal tears/dialysis
Juvenile rheumatoid arthritis
Retinal detachment secondary to choroidal coloboma
Retinal detachment in “morning glory” syndrome or optic nerve colobomas
Complications of retinal angiomatosis
Combined hamartoma of the retina and retinal pigment epithelium
Viral retinitis—cytomegalovirus, acute retinal necrosis
Intraocular infections—bacterial, viral, fungal, parasitic
Inflammatory conditions—sarcoidosis, Behçet’s syndrome, uveal effusion
but additional surgical viewing lenses (e.g., prism lenses, lenses of higher refractive index) have been developed to improve intraoperative visualization. Of increasing acceptance is the use of wide-field or panoramic viewing systems based on the principles of binocular indirect ophthalmoscopic visualization. Such systems offer an expanded visualization area and increased depth of focus but require that an image inverter be mounted on the microscope. Similarly, it is possible to perform pars plana vitrectomy using the binocular indirect ophthalmoscope rather than an operating microscope for illumination and observation.
Lensectomy is indicated when cataract prevents visualization of the fundus or when the lens is subluxated. Also, the lens is removed if vitreoretinal traction located at or anterior to the vitreous base must be dissected, which is most frequently seen in proliferative vitreoretinopathy (PVR) and trauma. Ultrasonic fragmentation of the lens is usually approached from the pars plana with the lens equator entered by the fragmenter probe. If no IOL is to be placed, the capsule is excised completely using the vitreous cutter or removed en bloc with forceps.
In some clinical situations, it has become increasingly common to combine standard phacoemulsification, using an acrylic foldable IOL, with vitrectomy.  Such an approach should not be employed when extensive anterior membrane dissection is required.
The main types of vitreous cutting technology employed are the guillotine and rotary cutters. The guillotine cutter is a 20-gauge blunt instrument with a side port through which tissue is aspirated and cut by an inner sleeve that moves along the long axis of the probe. Currently, cutting speeds of up to 2500 cuts/minute are attainable. Higher cutting speeds result in less traction on the tissue and, theoretically, fewer iatrogenic tears. Rotary cutters have a port closer to the tip of the probe and cut tissue using an inner cutting blade that spins inside the outer needle. Because the port is closer to the tip of the instrument, it is possible to cut closer to the surface of the retina. However, rotary cutters are more costly to produce and are not available as disposable instruments.
Epiretinal Membrane Dissection
Two types of epiretinal proliferation are encountered:
• Fibrovascular proliferation, which contains neovascularization, most commonly seen in proliferative diabetic retinopathy (PDR);
• Nonvascular membranes, found in PVR and macular pucker.
The surgical goals are to separate the posterior hyaloid from the retinal surface peripherally and to remove the epiretinal proliferative tissue or release its tractional effects centrally ( Fig. 104-1 , A). Surgical techniques employed to remove the proliferative tissue are:
• Delamination; and
• En bloc dissection.
The dissections are achieved using microsurgical instruments such as scissors that cut perpendicularly across fibrovascular tissue or scissors that have curved or horizontally oriented blades to cut between the retinal attachments of the proliferative tissue. The use of lit, multifunction instruments allows bimanual delamination of tissue, which can be carried out more safely and
Figure 104-1 Proliferative diabetic retinopathy. A, Severe tractional retinal detachment with vitreous hemorrhage secondary to proliferative diabetic retinopathy. B, After vitrectomy and epiretinal membrane removal, the retinal anatomy is restored.
with less bleeding. Attainment of the surgical objectives results in a stabilization of the retinopathy and vision ( Fig. 104-1 , B).
Nonvascular epiretinal membranes are found in PVR and, in a less severe form, macular pucker. Such membranes may adhere strongly to the surface of the retina and are best removed using end-gripping membrane forceps; a bimanual approach using an illuminated membrane pick and forceps reduces the possibility of the formation of iatrogenic retinal tears.
It is recognized now that mechanical effects of the posterior hyaloid at the vitreoretinal interface may result in macula hole formation and central visual loss. The actual structural changes within this layer of cortical vitreous that cause retinal pathology are unclear. A critical step in the surgical management is separation of the posterior hyaloid from the retina. After a central vitrectomy has been performed, the adherent layer of cortical vitreous at the vitreoretinal interface is engaged and elevated using a silicone tip cannula at high aspiration levels. The posterior hyaloid is most adherent at the optic disc and at the macular region. After separation of the hyaloid, noted by observation of the Weiss ring, the vitreous layer is excised out to the periphery.
Perfluorocarbon liquids are useful as an intraoperative mechanical tool. The various perfluorocarbon liquids currently used in vitreous surgery have different physical and optical properties. Perfluoro-n-octane, because of the better visibility it allows, low viscosity, and high vapor pressure, is the most commonly used perfluorocarbon liquid. Giant retinal tears with large, inverted posterior flaps can be repositioned easily into their normal anatomical position, which allows the successful management of this condition without the use of special equipment to rotate the patient intraoperatively.
In PVR, as perfluorocarbon liquid flattens the posterior retina, retinal folds are opened and allow traction and visualization of additional membranes ( Fig. 104-2 ). A posterior retinotomy for internal drainage of subretinal fluid is no longer necessary. The retina is stabilized as membrane dissection proceeds, and large retinotomies, when necessary, can be carried out more safely.
Figure 104-2 Ability of perfluorocarbon liquids to reattach mechanically posterior retina in proliferative vitreoretinopathy. Simultaneously, subretinal fluid is displaced anteriorly and out through peripheral retinal breaks.
Other applications of perfluorocarbon liquids are to float dislocated lens fragments or dislocated IOLs anteriorly, to provide intraocular hemostasis by localization of bleeding, and to express liquefied subretinal blood from under the retina.
Laser photocoagulation is applied around retinal breaks and circumferential retinotomies; in general, two to three rows of treatment are adequate. In more advanced cases of retinal detachment, such as PVR, laser spots may be placed contiguously in two or three rows on the anterior slope of the scleral buckle. In PDR, scatter photocoagulation is applied peripherally to reduce the risk of neovascular glaucoma. Recent experience with submacular surgery suggests that small, posterior retinotomies do not require laser photocoagulation.
Gas and Silicone Oil Tamponade
The final step in vitreous surgery is to decide whether it is necessary to fill the vitreous space using a tamponade agent. An automated air-infusion pump is used to perform the fluid-air exchange. A flute needle is used actively or passively to aspirate the intraocular fluid as air is infused through the infusion line. The entry of an air bubble into the vitreous results in an altered optical power of the eye and, as a consequence, different contact lenses are required to compensate for these changes.
Potential Complications of Vitreous Surgery
Posterior retinal breaks
Peripheral retinal breaks
Choroidal hemorrhage (rare)
Rhegmatogenous retinal detachment
Elevated intraocular pressure (multiple potential causes)
• neovascular glaucoma
• angle-closure glaucoma
• inflammatory debris
• corticosteroid response
• overfill with gas
Anterior hyaloidal fibrovascular proliferation
Fibrin deposition in the anterior chamber (not rare, especially in diabetics)
Progressive nuclear sclerosis (almost universal in phakic eyes)
Endophthalmitis (rare —1 in 2000)
In case no retinal detachment exists, a bubble tamponade may be unnecessary; but in some of these eyes, air is used to smooth out retinal folds or to allow visualization through a hemorrhagic medium postoperatively. In macular hole surgery, a longer lasting gas bubble is useful as its buoyant force may help close the hole. When retinal detachment is present, the subretinal fluid must be evacuated to achieve a complete fill with gas and ensure that the retina flattens without posterior folds. Perfluorocarbon liquid may be injected to flatten the retina up to the level of peripheral retinal breaks—the posterior subretinal fluid is expressed anteriorly. Internal drainage of the remaining subretinal fluid is accomplished by placement of the aspirating needle through the retinal break as air enters the eye. The descending air bubble flattens the anterior retinal detachment and forces the anterior subretinal fluid through the retinal break. When the subretinal fluid has been aspirated completely or nearly completely, the perfluorocarbon liquid may be removed.
The type of gas used is dependent on the individual clinical situation.  In eyes that have a simple retinal detachment, the role of the gas bubble is to allow adequate time for the chorioretinal adhesion from laser treatment to form. Usually, air or sulfur hexafluoride, which persists for 10–14 days, may be used. For more complex retinal detachments, such as PVR, trauma, and giant retinal tears, a longer lasting gas bubble is usually required. Perfluorohexane or perfluoropropane gases are chosen frequently for these situations.
Silicone oil tamponade may also be used as a long-term tamponade agent. This clear viscous liquid, which is immiscible with water, replaces the vitreous. Its surface tension and mild buoyant force mechanically hold the retina against the choroid. The advantage of silicone oil is that the patient has vision through the oil bubble and that extensive prone-head positioning (required with gas bubbles) is unnecessary. However, silicone oil may require surgical removal months after the retina has been reattached. The results of a multicenter, randomized clinical trial, in which the use of perfluoropropane gas was compared with the use of silicone oil for the treatment of severe PVR, found no statistically significant difference in the final retinal reattachment rate between the two modalities.
TABLE 104-1 — SURGICAL OUTCOMES IN VITREOUS SURGERY
Diabetic vitreous hemorrhage
89% improvement with clear vitreous 
Diabetic traction retinal detachment
66–95% retinal reattachment rate
94% final retinal reattachment rate
Giant retinal tears
96% final retinal reattachment rate
78–87% visual improvement by 2 Snellen lines
Idiopathic macular hole
80–94% holes closed
Choroidal neovascularization (idiopathic, presumed histoplasmosis)
58–63% visual improvement if ingrowth site is juxtafoveal or extrafoveal 72% no change in visual acuity if ingrowth site is subfoveal
Dislocated lens fragments
68% final visual acuity 20/40 (6/12) or better
Many of the potential complications of vitreous surgery may be realized later. The rate of complications has decreased gradually as improvements in technology have been introduced. However, experience, surgical skill, and training are also significant factors that can reduce the rate of complications. The more widely described intraoperative and postoperative complications encountered with vitreous surgery are given in Box 104-2 .
The introduction of new surgical techniques and instrumentation and improved knowledge of the pathophysiology of abnormal vitreoretinal structural changes have resulted in a steady improvement in the anatomical and visual results of vitreous surgery. Some of the results reported for the most common indications of vitrectomy are given in Table 104-1 and represent significant advances in the surgical treatment of retinal disorders.
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