Vitrectomy is an intraocular surgery during which the vitreous is removed to allow for adjunctive procedures to repair retinal and/or macular pathology or to remove foreign, abnormal, or dislocated tissue or material from the posterior segment or to place therapeutic medications, devices, or tamponades into the eye.
Introduction
Since its genesis, remarkable advances in vitreous surgery have established this microsurgical procedure as the second-most common intraocular operation after cataract extraction. Progress in two major areas has fueled the extraordinarily rapid growth in vitreous surgical techniques:
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Understanding of the pathoanatomical changes that affect the retina and vitreous.
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Introduction of new technology and instrumentation.
In the early years, vitrectomy was used to restore ambulatory vision in eyes that were otherwise 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 advances in technology continued and the safety of the vitrectomy procedure was established, the focus shifted to newer applications (e.g., macular surgery). The goals of this surgery are to improve and restore central visual acuity in such conditions as macular pucker, macular hole, and retinal detachment.
Preoperative Evaluation and Diagnostic Approach
The preoperative evaluation of patients who are to undergo vitrectomy includes a careful examination of the eye and assessment of the patient’s medical status and risk of anesthesia-related complications. The surgeon reviews the planned procedure with the patient to explain expected outcomes and potential benefits and risks.
Slit-lamp examination is used to evaluate the anterior segment structures, whereas indirect biomicroscopy allows for assessment of vitreoretinal anatomy. When a gas bubble tamponade is planned, the depth of the anterior chamber is assessed because a large bubble may result in shallowing and 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 pseudo-phakic eyes, the type of intraocular lens (IOL) and its composition are studied. Because 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 reduces the clarity of the optical zone. Gonioscopic evaluation is carried out in patients with diabetes and those who have inflammatory conditions.
The status of the vitreous is best studied using indirect biomicroscopy—either a noncontact +78.00 diopters (D) or +90.00 D lens or a contact 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 (ERM) proliferation, the location of retinal breaks, and anatomical changes in the vitreous base and peripheral retinal structures. Optical coherence tomography (OCT) as an adjunctive diagnostic tool has revolutionized the assessment of the vitreous–retinal interface as well as the retina, retinal pigment epithelium (RPE), and subretinal space at a close to ultrastructural level in a noninvasive fashion. This has greatly facilitated the distinction between “true” macular holes, pseudo- and lamellar holes, as well as cystic macular edema. Sensitivity, specificity, and reproducibility exceed that of a contact lens examination. It is also increasingly being used to help prognosticate surgical outcomes for macular hole and macula-off detachment surgery.
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 trauma 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 6.12.1 . 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.
Diabetic Retinopathy
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Nonclearing or repeated vitreous hemorrhage
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Traction retinal detachment
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Combined traction and rhegmatogenous retinal detachment
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Progressive fibrovascular proliferation
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Macular distortion by fibrovascular proliferation
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Macular edema that results from a taut posterior hyaloid
Retinal Detachment
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Retinal detachment with proliferative vitreoretinopathy
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Giant retinal tears
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Retinal detachment with posterior retinal breaks
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Some primary retinal detachments
Complications of Anterior Segment Surgery
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Dislocated lens fragments
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Dislocated intraocular lens
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Aphakic or pseudo-phakic cystoid macular edema
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Endophthalmitis
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Choroidal hemorrhage
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Epithelial downgrowth
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Anesthetic needle perforation
Trauma
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Hyphema evacuation
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Traumatic cataract or dislocated lens
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Posterior penetration injuries with vitreous hemorrhage and/or retinal detachment
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Reactive intraocular foreign body
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Subretinal membranes or hemorrhage
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Traumatic macular holes
Macular Surgery
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Macular pucker
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Macular hole
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Massive subretinal hemorrhage
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Vitreomacular traction syndrome
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Myopic traction maculopathy
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Retinal detachment secondary to optic pit, and other optic nerve anomalies
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Transplantation of retinal photoreceptors or retinal pigment epithelium
Pediatric Retinal Disorders
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Retinopathy of prematurity
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Persistent hyperplastic primary vitreous
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Familial exudative vitreoretinopathy
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Giant retinal tears/dialysis
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Juvenile retinoschisis
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Juvenile rheumatoid arthritis
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Retinal detachment secondary to choroidal coloboma
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Retinal detachment in “morning glory” syndrome or optic nerve colobomas
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Gene therapy for treatment of retinal degenerations
Tumors
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Choroidal melanoma
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Complications of retinal angiomatosis
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Combined hamartoma of the retina and retinal pigment epithelium
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Intraocular lymphoma
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Diagnostic vitrectomy, fine needle aspiration
Uveitis
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Viral retinitis—cytomegalovirus infection, acute retinal necrosis
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Intraocular infections—bacterial, viral, fungal, parasitic
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Ophthalmomyiasis
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Inflammatory conditions—sarcoidosis, Behçet’s syndrome, uveal effusion
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Pars planitis
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Whipple’s disease
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Familial amyloidosis
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Hypotony
Anesthesia
The majority of vitrectomies are carried out under local anesthesia (retrobulbar block, peribulbar block, or subconjunctival irrigation) with monitored anesthesia care. In instances of extreme patient apprehension or an inability to cooperate, general anesthesia is required. When using general anesthesia and intraoperative gas administration, 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.
General Techniques
Microincision vitrectomy uses instruments of 23-gauge, 25-gauge, or 27-gauge caliber ( Fig. 6.12.1 ) and has replaced standard 20-gauge vitrectomy for most cases in the hands of most surgeons. Microincision vitrectomy employs self-retaining microcannula ports, which are inserted transconjunctivally by using trocar needles. During insertion, the needles are directed at such an angle that a beveled self-sealing incision results. The cannulas are placed 3.5–4.0 mm posterior to the corneal limbus, depending on the phakic status of the eye. Usually the inferior cannula is connected to an infusion line to replace the vitreous removed with balanced saline. A vitreous cutter probe, and a fiberoptic light probe are inserted through the superior sclerotomy openings. “Valved” cannulas, which have a thin membrane covering the entrance of the cannula, are increasingly utilized so that fluid egress from the eye is limited during the procedure and turbulent flow and pressure oscillation in the eye are minimized. Additional light fibers of 2-gauge or 27-gauge (“chandelier” lighting) can be inserted through the pars plana to supplement the light from the fiberoptic probe or allow two instruments to be placed into the eye for bimanual dissection. An assortment of additional instruments, such as forceps, scissors, and laser probes, is also available for membrane manipulation ( Fig. 6.12.2 ). Even the most complex vitrectomies can be done with smaller gauges, with 20-gauge instruments still required to remove dense lens fragments or foreign bodies. Most of the small-gauge incisions are self-sealing, but occasionally, a single transconjunctival suture is necessary to close a leaky opening.
A high-resolution surgical microscope is used to view the fundus during surgery. A plano-concave contact lens is used most commonly, 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 contact or noncontact wide-field or panoramic viewing systems based on the principles of binocular indirect ophthalmoscopic visualization ( Fig. 6.12.3 ). Such systems offer an expanded visualization area and increased depth of focus but require that an image inverter be mounted on the microscope. Recently, systems using binocular video cameras placed onto the body of a surgical microscope have been developed for vitrectomy. The surgeon views a large surgical monitor with three-dimensional glasses and is able to perform the delicate surgical maneuvers required. Advantages for such an approach are that lower illumination is required, and ergonomically, the surgeon’s neck and back are less prone to stress.
Specific Techniques
Lensectomy
Lensectomy is indicated when cataract prevents visualization of the fundus or when the lens is subluxated. Furthermore, 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 fragmentation probe. If no IOL is to be placed, the capsule is excised completely by using the vitreous cutter or removed en bloc with forceps.
It has become increasingly common to combine standard phacoemulsification, using an acrylic foldable IOL, with vitrectomy. This combined approach speeds the recovery time for stabilization of visual acuity.
Vitreous Cutters
The vitreous cutting technology used is the guillotine cutter. This instrument, which comes in 20, 23, 25, and 27 gauges, consists of a round needle-like shaft small opening near the tip. Tissue is aspirated into the port and cut by an inner hollow sleeve that moves back and forth along the long axis of the probe. Currently, cutting speeds of up to 10 000 cuts/min are attainable. Higher cutting speeds result in less traction on the tissue, and theoretically, fewer iatrogenic tears would occur when the probe is working near the surface of the retina. Higher cutting rates have also been introduced by modifying the inner cutting sleeve to have two openings so that with each stroke, the tissue is cut twice with one cycle. Enhancements, such as placing the port closer to the end of the probe or beveling the end of the probe, also allow the port to be placed closely to the tissue that is being cut ( Fig. 6.12.4 ).
