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Principles and Techniques of Macular Surgery

Gerardo García-Aguirre Raúl Velez-Montoya Hugo Quiroz-Mercado

HISTORY

Since its inception in the early sixties (1, 2), vitrectomy procedures have been performed in order to treat diverse vitreoretinal diseases. At the beginning, when the technique was at its infant stages (when it was performed as “open sky” vitrectomy), its purpose was mainly to treat abnormal vitreous conditions, most of the times with disappointing results. It was not until the seventies that Dr. Robert Machemer (3, 4) developed a pars plana approach using specialized instruments introduced through small incisions, while maintaining an adequate intraocular pressure and thus limiting damage to the anterior segment while allowing for maneuvers in the posterior segment. This surgical advance offered vitreoretinal surgeons a whole new array of tools and techniques for the treatment of several vitreoretinal pathologies.

During its early phases, pars plana vitrectomy was performed for nonclearing vitreous hemorrhages or complicated cases of retinal detachment. It was in 1978 when Dr. Machemer (5) again reported the first case of vitrectomy and epiretinal membrane peeling, thus giving birth to macular surgery. In 1991, Drs. Kelly and Wendel (6) provided another breakthrough in macular surgery, when they published the results of a pilot study of vitreous surgery for idiopathic macular holes. Ever since, an increasing number of surgeons have adopted vitrectomy as the treatment of choice for diverse macular pathologies and refined its instruments and methods, broadening the indications for vitrectomy and improving anatomic and visual results.

PREOPERATIVE CONSIDERATIONS

In order to improve the surgical outcome on a patient who will undergo macular surgery, a careful surgical plan must be elaborated, based on a thorough preoperative evaluation that should include a complete eye examination. Other factors, such as the general medical condition of the patient, must be considered. Before surgery, the patient must be informed about the potential risks and benefits expected from the procedure as well as the anticipated outcome based on the severity of the disease being treated.

OPERATIVE CONSIDERATIONS

Preoperative Instrument Check

Before administering anesthesia, a preoperative instrument check must be performed. The microscope must be inspected for adequate lighting, pedal function, and X-Y mobility. The vitrectomy console must have sufficient gas pressure. The cut-suction probe must be checked for adequate cutting rate and suction. Tamponade agents such as gas or silicone oil must be available. Foot pedals should be placed so that the surgeon can sit comfortably while maintaining balance.

ANESTHESIA

For most vitrectomy procedures, local anesthesia (retrobulbar or peribulbar) with monitored anesthetic care is preferred. However, general anesthesia is indicated in some cases (such as performing procedures in children or in extremely anxious patients). Peribulbar or retrobulbar block is performed with a 50:50 mixture of 2% lidocaine and 0.75% bupivacaine, delivering 3 to 4 ml of anesthetic in the retrobulbar/peribulbar space, in order to achieve adequate anesthesia and akinesia. Facial block may be performed, according to the preference of the surgeon.

OPERATIVE FIELD PREPARATION

After the patient is comfortably placed in the operative chair or table, the head is positioned with the face directed toward the ceiling. Air and/or supplemental oxygen can be delivered through a nasal cannula. The periocular skin and lids are then prepped with 5% povidone-iodine. Care must be taken so that povidone-iodine enters the conjunctival cul-de-sac, thereby contacting the ocular surface.

A forehead drape should be placed around the head and another should cover the inferior part of the face and the rest of the body. Then, a plastic adhesive drape is placed over the eye, covering the eyelids and keeping the eyelashes out of the field as much as possible. A plastic bag is placed in the temporal side of the adhesive drape in order to collect fluids. A lid speculum is then placed.

SCLERAL INCISIONS

If using conventional 20-gauge pars plana vitrectomy, fornix-based conjunctival flaps should be created, exposing the sclera at the inferotemporal, superotemporal, and superonasal sectors. An incision is then performed with an microvitreo retinal (MVR) blade in the inferotemporal quadrant. The distance from the corneoscleral limbus varies: 4 mm in phakic patients, 3.5 mm in pseudophakic patients or patients with planned simultaneous cataract extraction, and 3 mm in aphakic patients. A single- or double-bite 6- or 7-0 Vicryl suture is placed, and an infusion cannula is inserted and secured with the preplaced suture. The superotemporal and superonasal sclerotomies are performed with an MVR blade, just superior to the meridians of the horizontal rectus insertions, in order to serve as ports for the diverse intraocular instruments that will be used during the procedure.

If using 23-gauge or 25-gauge instruments, trocars are placed transconjunctivally in an oblique fashion in order to improve wound closure. The inferotemporal trocar should be placed first and the infusion cannula must be connected to it. Superotemporal and superonasal trocars are placed after the infusion is set.

CORE VITRECTOMY

Removal of the central vitreous is the first step in every macular procedure. The specifications of microscopes, viewing systems, and instruments necessary for vitrectomy are reviewed in the additional chapters of this section. It is of critical importance that the tip of the infusion cannula be visualized through the pupil inside the vitreous cavity before opening the infusion. After the infusion has been opened, the tip of the cut-suction probe is placed at the center of the vitreous cavity and the pedal is activated. A relatively low cutting rate (800 to 1200 cuts per minute) and a vacuum of 100 to 150 mm Hg are recommended at this time for quicker vitreous aspiration (higher vacuum is recommended for 23-gauge and 25-gauge vitrectomy). The port of the suction probe should be directed toward the vitreous to be cut. If the vitreous is free of traction, it will readily engage the port. If the vitreous is under traction, the port must be placed in contact with the vitreous to be cut. If a vitreous band is present, it must be engaged directly.

POSTERIOR HYALOID REMOVAL

After core vitrectomy has been performed, the next important step is posterior hyaloid separation and removal. The posterior hyaloid is more firmly adhered around the optic disc at the foveola and over retinal blood vessels (7). Its removal is of key importance because if left attached, it may provide a surface for cellular proliferation or contribute to remaining postsurgical vitreoretinal traction. The posterior hyaloid may be removed using the cut-suction probe or using a silicone tip cannula, although other methods have been advocated.

CUT-SUCTION PROBE

Posterior hyaloid removal using the cut-suction probe is recommended, mainly because there is no need to change the instrument used in the previous step (core vitrectomy). The mode is set to suction only, with a vacuum of 150 to 200 mm Hg. The infusion pressure may need to be elevated in order to avoid hypotony. The tip of the probe is then positioned just above the optic disc on the nasal side, and suction is applied (Fig. 15-1). The probe is then pulled anteriorly, away from the optic disc (8). If the maneuver is successful, it will break the attachments of the posterior hyaloid to the area around the optic disc. This in turn will allow the passage of fluid to the retrohyaloidal space and facilitate the dissection. The detachment of the posterior hyaloid usually is visualized as a dark circle or shadow at the surface of the retina. After the posterior hyaloid has been detached, the mode is set to cut suction, and the remaining vitreous can be cut and aspirated.

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