Ординатура / Офтальмология / Английские материалы / Bimanual Phaco Mastering the Phakonit MICS Technique_Agarwal_2004

Figure 19-4. Bimanual vitrectomy. Please note separate vitrectomy probe and infusion cannula.

Unplanned posterior capsulotomy that violates the anterior vitreous hyaloid face tends to induce vitreous loss. Factors which inhibit early recognition of a posterior capsular rent by the surgeon (ie, obstruction of view by a large and opaque nuclear fragment, may increase the tendency for greater vitreous loss).

In the event of a posterior capsular rent with no vitreous loss, vitrectomy may not be required. Nevertheless, the flow rate and infusion should be decreased to avoid subsequent anterior vitreous herniation. However, a vitrectomy is mandatory when vitreous loss is confirmed. A single vitrectomy probe with a coaxial cannula should generally be avoided in favor of a bimanual vitrectomy technique using separate infusion cannula and vitrectomy probe (Figure 19-4). A coaxial infusion probe may require enlargement of the original incisional wound. Coaxial infusion also tends to open up the posterior capsular flap and hydrate the vitreous more than a separate infusion cannula, thus permitting more anterior vitreous prolapse. With the bimanual technique, a limited anterior vitrectomy is performed and the main body of the vitreous is not disturbed. During the procedure, vitreous should be aspirated downward below the plane of the posterior capsule. Irrigation should be gentle and limited to the anterior chamber. Following vitrectomy, a posterior intraocular lens (IOL) may be inserted in front of the anterior capsule in the ciliary sulcus, if an adequate capsular rim is present. Vitreous loss can be prevented or minimized by avoiding phacoemulsification on the posterior surface of the nucleus. Improper vitrectomy can result in postoperative malpositioning of the IOL (Figure 19-5) and severe intraocular inflammation (Figure 19-6).

NUCLEAR DISLOCATION

If the posterior capsular rent is large, the nucleus may migrate into the posterior vitreous cavity. Since an exposed nucleus is strongly antigenic and may cause a severe ocular phacoanaphylactic or phacotoxic reaction, its removal is mandatory. A soft nucleus can be removed with a vitrectomy probe alone, but a hard one requires posterior phacofragmentation, usually via a pars plana approach. An alternative method for removing a large and hard nuclear fragment is floating it anteriorly with perfluorocarbon liquids (PFCL) after a posterior vitrectomy (see Chapter 20). The anteriorly displaced lens fragment can then be delivered out of an enlarged corneal-scleral limbal

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Figure 19-5. Haptic of an IOL in the anterior chamber (courtesy of Dr. Prakash, DP).

Figure 19-6. Severe inflammatory reaction in the anterior chamber (courtesy of Dr. Prakash, DP).

wound. One can also use the FAVIT technique (see Chapter 20) for removing dropped nuclear pieces.6

EXPULSIVE HEMORRHAGE

Expulsive suprachoroidal hemorrhage rarely occurs in conjunction with a 1.0-mm incision associated with bimanual phaco. This small beveled incision is self-sealing, and therefore, usually prevents extrusion of intraocular contents associated with the suprachoroidal hemorrhage. In the event of a hemorrhagic choroidal detachment, the performance of a posterior sclerotomy to allow posterior release of the suprachoroidal hemorrhage and a rapid closure of the wounds minimize the chance of an expulsive hemorrhage.

CONVERSION TO

EXTRACAPSULAR CATARACT EXTRACTION

Upon the first sign of excessive corneal clouding or anterior vitreous prolapse, the surgeon should consider converting bimanual phaco to extracapsular cataract extraction (ECCE), in order to enhance the likelihood of achieving good functional visual outcome. Conversion should be undertaken preferably before excessive corneal endothelial damages and capsular rupture occur.

Planned conversion to ECCE is better than forced conversion. The surgeon should enlarge the limbal wound for extracapsular delivery of the nucleus from the posterior chamber, upon the first sign of anterior vitreous herniation. A lens loop or equivalent instrument may be inserted under the nucleus for its expression out of the eye. After the nucleus is out, an irrigation/aspiration handpiece with a 0.5-mm tip is employed with low vacuum for lenticular cortical clean-up. However, lens fragments dislocated into the vitreous cavity are left alone for subsequent management with vitreoretinal techniques. The cataract surgeon unfamiliar with vitreoretinal techniques should refer the patient to a vitreoretinal surgeon. Attempts in removing posteriorly dislocated lens fragments without proper vitreoretinal techniques tend to cause retinal complications. In the event of vitreous loss, cortical aspiration may be difficult, and a vitrectomy probe is usually a better tool for completing the cortical clean-up.

MANAGEMENT OF A MALPOSITIONED IOL

Disturbing visual symptoms such as diplopia, metamorphopsia, and hazy images are associated with a dislocated IOL (Figure 19-7). If not properly managed, a malpositioned IOL may also induce sight-threatening ocular complications, including persistent cystoid macular edema, intraocular hemorrhage, retinal breaks, and retinal detachment. Contemporaneous with advances in bimanual phaco microsurgical techniques for treating cataracts, a number of highly effective surgical methods have been developed for managing a dislocated IOL (Figure 19-8). They include IOL manipulation with perfluorocarbon liquids, scleral loop fixation, use of a snare, employing 25gauge IOL forceps, temporary haptic externalization, as well as managing the single plate implant and two simultaneous intraocular implants. One excellent method is the use of a diamond tipped forceps to hold the IOL and bring it anteriorly after vitrectomy (Figure 19-9). The primary aim of such methods is to reposition the dislocated IOL close to the original site of the crystalline lens in an expeditious manner whenever possible, and with minimal morbidity, enhancing the chance of good visual outcome.

PERFLUOROCARBON LIQUIDS

Chang popularized the use of perfluorocarbon liquids for the surgical treatment of various vitreoretinal disorders. Due to their heavier-than-water properties and their ease of intraocular injection and removal, perfluorocarbon liquids are highly effective for flattening detached retina, tamponading retinal tears, limiting intraocular hemorrhage, insulating the retina from damages, as well as floating dropped crystalline lens fragments and dislocated IOLs. The anterior displacement of a dislocated IOL by perfluorocarbon liquids facilitates its removal or repositioning.

Types of Perfluorocarbon Liquids

Four types of perfluorocarbon liquids are frequently employed for intraocular surgery. They include:

1.Perfluoro-N-Octane.

2.Perfluoro-Tributylamine.

3.Perfluoro-Decaline.

4.Perfluoro-Phenanthrene.

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Figure 19-7. Dislocated plate haptic IOL on the retina.

Figure 19-8. IOL lying over the disc.

Figure 19-9. Diamond tipped forceps lifting a looped IOL lying on the retina after a vitrectomy.

TA B L E 19-2

PROPERTIES OF PERFLUOROCARBON LIQUIDS

Their physical properties are outlined in Table 19-2.

THE SNARE

Grieshaber first manufactured a snare that was designed by Packo in the early 1990s. It consists of a 20-gauge tube and a handle with a movable spring-loaded finger slide for adjusting the size of a protruding polypropylene loop. The distal portion of the tube with the polypropylene loop is inserted through an anterior sclerotomy for engaging a dislocated haptic in the vitreous cavity. Once the looped haptic is pulled up against the anterior sclerotomy, the external portion of the polypropylene loop is cut free and guided through a 30-gauge needle for anchoring by the anterior sclerotomy (Figure 19-10).

TEMPORARY HAPTIC EXTERNALIZATION

Chan first described this method in 1992. Its main features involve temporary haptic externalization for suture placement after a pars plana vitrectomy, followed by reinternalization of the haptics tied with 9-0 or 10-0 polypropylene sutures for secured anchoring by the anterior sclerotomies. The details of this technique include the following:5

1.A three-port pars plana vitrectomy is performed for the removal of the anterior and central vitreous adjacent to the dislocated IOL, in order to prevent any vitreoretinal traction during the process of manipulating the IOL.

2.Two diametrically opposed limbal-based partial thickness triangular scleral flaps are prepared along the horizontal meridians at 3 and 9 o’clock. Anterior sclerotomies within the beds under the scleral flaps are made 1.0 to 1.5 mm from the limbus (Figure 19-11A). As an alternative to the scleral flaps, the anterior scleromies may be made within scleral grooves at 1.0 to 1.5 mm from the horizontal limbus.

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Figure 19-10. The Grieshaber snare consists of a 20-gauge tube and handle with a movable spring-loaded finger slide for adjusting the amount of a protruding polypropylene suture loop. The suture loop is inserted posteriorly to engage a dislocated haptic. The external portion of the suture loop is then cut free and guided through a 30-gauge needle for anchoring at the sclera, after the engaged haptic is pulled up against the anterior sclerotomy.

3. .A fiberoptic light pipe is inserted through one of the posterior sclerotomies, while a pair of fine non-angled positive action forceps (eg, Grieshaber 612.8) is inserted through the anterior sclerotomy of the opposing quadrant to engage one haptic of the dislocated IOL for temporary externalization (Figure 19-11B). A doublearmed 9-0 (Ethicon TG 160-8 plus, Somerville, NJ) or 10-0 polypropylene suture (Ethicon CS 160-6, Somerville, NJ) is tied around the externalized haptic to make a secured knot. The same process is repeated for the other haptic after the surgeon switches the instruments to his opposite hands.

4.The externalized haptics with the tied sutures are re-internalized through the corresponding anterior sclerotomies with the same forceps (Figure 19-11C). The surgeon anchors the internalized haptics securely in the ciliary sulcus by taking scleral bites with the external suture needles on the lips of the anterior sclerotomies. By adjusting the tension of the opposing sutures while tying the polypropylene suture knots by the anterior sclerotomies, the optic is centered behind the pupil, and the haptics are anchored in the ciliary sulcus.

ONE-PIECE PLATE IOL

The surgeon may extend the tip of a lighted pick under the edge of the silicone plate implant to gently elevate it off the retinal surface. The elevated edge is then grasped with the intraocular forceps for the repositioning or removal of the implant. Alternatively, the plate implant may be brought anteriorly by hooking the lighted pick through one of its positioning holes, and then grasped with forceps at the anterior or mid-vitreous cavity (Figure 19-12).

Figure 19-11. Temporary haptic externalization.

Figure 19-12. The slippery plate implant may be lifted on its edge or hooked through a positioning hole with a lighted pick, and then grasped with intraocular forceps for its repositioning or removal.

MISCELLANEOUS IOL PROBLEMS

A number of problems may be associated with the IOL itself. For instance, a defective IOL due to improper manufacturing may cause increased tendency for opacification of the IOL (Figure 19-13). The IOL may also decenter or tilt (Figure 19-14), and extrude (Figure 19-15).

ENDOPHTHALMITIS

Introduction

Despite numerous recent advances in its treatment, infectious endophthalmitis continues to be one of the most serious complications in ophthalmology. The infectious organism associated with endophthalmitis causes prominent ocular inflammation and

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Figure 19-13. IOL opacification.

Figure 19-14. IOL decentration.

Figure 19-15. IOL extrusion.

toxic reactions, leading to severe intraocular tissue damages and the consequential marked visual loss.

Techniques of Specimen Collection

Aqueous and vitreous specimens may be obtained in an office setting or at the time of a vitrectomy. In the former situation, careful administration of local anesthesia (topical, subconjunctival, peribulbar, or retrobulbar) and sterile prepping with 5% povi- done-iodine solution are recommended. A small volume of aqueous specimen (0.1 to 0.2 mL) is then carefully withdrawn via a 27or 30-gauge needle at the limbus into a tuberculin syringe. The vitreous specimen may be obtained with one of the following two methods:

1.Needle tap: A 22to 27-gauge needle attached to a tuberculin syringe is inserted through the pars plana into the vitreous cavity for gentle aspiration of 0.1 to 0.3 ml of liquid vitreous. Excessive force must be avoided to prevent vitreoretinal traction. A “dry tap” requires the conversion to a mechanized biopsy.

2.Mechanized vitreous biopsy: A one-, two-, or three-port pars plana vitrectomy with a mechanized 20-gauge vitrectomy probe is employed for the biopsy. A small volume of undiluted specimen (up to 0.3 mL) from the anterior vitreous is collected into a sterile syringe connected to the aspiration line of the vitrectomy probe through gentle manual suction by a surgical assistant during the vitrectomy.

Diluted specimens collected into a larger syringe or into a vitrectomy cassette may also be concentrated either with the suction filtered technique or the centrifuged method (Figure 19-16A). The former involves passing the diluted specimens in an upper sterile chamber through a membrane filter with 0.45-µm pores into a lower chamber connected to suction. With the aid of sterile forceps and scissors or knives, the membrane filter containing the concentrated specimens is then cut into small pieces for direct inoculation on solid and into liquid media for cultures (Figure 1916B). Concentrated specimens scraped off the surface of the membrane filter are also applied on slides for preparation of various stains. The alternative centrifuged method requires the transfer of the diluted specimens into a sterile centrifuge tube for highspeed centrifuge. The sediments from the centrifuged tube are then processed for microbiological stains and cultures (Figure 19-16C).

Treatment of Endophthalmitis

The two fundamental therapeutic modalities for treating infectious endophthalmitis in the modern world comprise of antimicrobial therapy and vitrectomy (Figure 19-17). When appropriate, they may be supplemented with anti-inflammatory therapy for reducing damages induced by the infection. Applying effective strategies for antimicrobial therapy constitutes the most critical aspect of the management of endophthalmitis. The intravitreal dosage of drugs is shown in Table 19-3.

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Figure 19-16. Methods of collecting specimens in endophthalmitis. A) Undiluted aqueous and vitreous specimens may be directly inoculated onto culture media and used for smear preparation. B) Diluted vitreous specimen collected into a syringe or a cassette is either first concentrated by vacuuming the diluted fluid in a sterile upper chamber through a 0.45-µm membrane filter into a lower sterile chamber (suction filter method). C) Concentrated in a sterile centrifuge tube after performing high-speed centrifuge (centrifuge method). Small cut segments of the membrane filter with the concentrated specimens or the sediments from the centrifuged tube are inoculated into culture media and applied on slides for smear preparation.

Figure 19-17. Anterior chamber washout before vitrectomy. The technique of eliminating cloudy fibrin deposits, membranes, and hyphema from the anterior chamber is illustrated. A microsurgical hook or pick inserted at the limbus is used to scrape off the cloudy material from the IOL and iris surface before removing them with a vitrectomy probe from the anterior chamber. A separate probe also inserted at the limbus for anterior chamber infusion is often necessary to prevent chamber collapse. The posterior infusion fluid is not turned on until adequate media clarity is achieved to ascertain the proper location of the tip of the posterior infusion cannula.