Ординатура / Офтальмология / Английские материалы / The Art and the Science of Cataract Surgery_Boyd, Barraquer_2000
.pdf
T H E A R T A N D THE S C I E N C E OF C ATA R A C T S U R G E R Y
A. Extracapsular Cataract Extraction with Trabeculectomy
1. Separate Incisions
The cataract and trabeculectomy incisions are made separately at different sites. The cataract incision is made in the cornea and is a single 11 mm chord length corneal cataract incision. A 3 mm x 3 mm lamellar scleral trabeculectomy flap is made separately in the upper nasal quadrant in the sclera under fornix or limbus based conjunctival flap (Fig. 172). This approach has the disadvantage that it necessitates a corneal cataract wound for extracapsular surgery. This type of incision is no longer popular because of its tendency toward higher levels of astigmatism in the early postoperative phase before the corneal sutures are removed. This approach is a good technique for those surgeons using a small corneal incision for phacoemulsification combined with trabeculectomy (Fig. 187).
2. Compound Incision
By the term «compound incision» we mean that the surgeon combines a limbal 2-plane cataract incision of 9.5 mm or 10 mm chord length with a 3 mm x 3 mm 1/2 thickness lamellar scleral flap for the trabeculectomy (Fig. 173). Luntz prefers to place a trabeculectomy flap in the center of the cataract incision and this is a generally favored technique (Fig. 173). When the trabeculectomy flap is placed in the center of the cataract incision and the cornea-scleral trabeculectomy block measuring (2 mm x 2 mm) is removed from the scleral bed before removing the cataract, the total surface area of the cataract incision is increased at the site of maximum thickness of the lens during extraction for
intracapsular surgery or of a nuclear extraction for extracapsular surgery, thus facilitating their removal. This allows the use of an incision of smaller cord length - namely, 9.5 mm instead of the usual 11 mm chord length (Fig. 173).
Luntz points out that a matter of great importance in the architecture of this compound incision is that the continuity of the limbal scleral incision for the cataract removal is broken in the center by the intrusion of the trabeculectomy flap with its two radial incisions which are placed 3 mm apart. By breaking the continuity of the limbal scleral incision (the cataract portion of the incision) we introduce an element of instability into the incision. Part of the incision is parallel to the limbus (the cataract incision) and part of the incision is radial to the limbus (the trabeculectomy incision). Where the two meet at each side of the trabeculectomy scleral flap the incision, when stressed postoperatively (for example by squeezing of the eyelid or distortion of the globe) they can shift horizontally, vertically or obliquely, causing postoperative oblique or against the rule astigmatism. The ability of the incision to shift vertically is magnified if the cataract and trabeculectomy incisions meet at the limbus at a 90º angle. To minimize this effect, Luntz recommends that the cataract incision should be curved into the trabeculectomy incision forming a convex curve on each side of the cataract trabeculectomy incision junction (Fig. 173). This curving of the incision reduces any tendency for vertical shift. This can be enhanced by careful attention to placement of the interrupted sutures at the time of suturing the incision. Additional stability is imparted to the incision by placing the interrupted 10-0 nylon sutures radially in the cataract portion of the incision, and by placing the sutures in the curved junction between
304
C h a p t e r 12: Cataract Surger y in Complex Cases
Figure 172 A (left): Evolution of Types of Combined Cataract Extraction-Trabeculec- tomy Surgery - Type 1- Individual Surgical Sites - Surgeon’s View
The first method of combined cataract extraction with trabeculectomy involves two separate surgical sites. The cataract surgery is performed through a corneal incision (C). The trabeculectomy is performed by a standard technique at the limbus. Note separate 3 mm by 3 mm scleral flap (F) and 2 mm by 2 mm trabeculectomy window (W). Iridectomy (I). Limbus based conjunctival flap.
Figure 172 B (right): Evolution of Types of Combined Cataract Extrac- tion-Trabeculectomy Surgery - Type 1- Individual Surgical Sites - Cross Section View
In this cross-section view, you can instantly identify the anatomical structures involved in the combined procedure when using two individual surgical sites. Note the scleral trabeculectomy flap (F) separate from corneal cataract incision (C). Trabeculectomy window (W). Iridectomy (I). Limbus based conjunctival flap.
305
T H E A R T A N D THE S C I E N C E OF C ATA R A C T S U R G E R Y
the cataract and trabeculectomy portions at 45º to the incision line (Fig. 173).
Although this is a relatively stable compound incision, it is not as stable as a single unbroken incision and will induce more astigmatism, particularly oblique and against the rule astigmatism, than would be expected with a simple, unbroken cataract incision. An unbroken incision can be achieved by making the incision for the cataract surgery separate from the trabeculectomy (Fig. 172) or by using a large scleral bevel and combining both the trabeculectomy and the cataract wound within the unbroken incision (Figs. 174, 175).
Figure 173 A (above) : Evolution of Types of
Combined Cataract Extraction-Trabeculectomy
- Type 2- Combined Incision - Surgeon’s View
A combination of the cataract extraction and trabeculectomy incisions is seen in this surgeon’s view. Note the limbus based two-plane cataract incision (C) with cord length of 9.5 mm and centrally placed 3 mm by 3 mm scleral flap (F). Note the 2 mm by 2 mm trabeculectomy window
(W). The junction of the cataract incision and scleral flap is convex in shape (arrow) for a more stable wound closure. Iridectomy (I). Fornix based conjunctival flap.
Figure 173 B (below): Evolution of Types of Combined Cataract Extraction-Trabeculectomy - Type 2- Combined Incision - Cross Section View
This cross section view allows prompt identification of the tissues and technique involved as explained in Fig. 173 A. Compare the site of the cataract incision (limbus-based) and the combined scleral flap (F) with cataract incision in contrast with the individual surgical sites incision shown in Fig. 172 B.
306
C h a p t e r 12: Cataract Surger y in Complex Cases
Figure 174 A (left): Evolution of Types of Combined Extracapsular Cataract Extrac- tion-Trabeculectomy - Type 3- Single, Unbroken Tunnel Incision - Surgeon’s View
Development of the scleral tunnel incision for phacoemulsification has simplified the incision for combined extracapsular cataract extraction and trabeculectomy. A 9.5 mm to 10 mm cord length, 1/2- scleral thickness groove (S) is placed 1.5 mm posterior to the surgical limbus. A scleral tunnel is dissected to the limbus, penetrating into the anterior chamber in the center of the groove incision and widened on each side over the full 10 mm length of the groove using a crescent knife and corneo-scleral scissors (C) (See Fig.178). The resulting scleral flap (F) is reflected. A trabeculectomy window (W) is performed under this scleral flap, contained within the scleral bed. Iridectomy (I) shown in Fig. 174- B. Fornix based conjunctival flap.
Figure 174 B (right): Evolution of Types of
Combined Extracapsular Cataract Extraction-
Trabeculectomy - Type 3- Single, Unbroken
Tunnel Incision - Cross Section View
The angled view of the structures involved in the tunnel incision shows the difference in this surgical approach to the two previous types of incision (Figs. 172-B and 173-B). The anatomical structures and technique of incision are explained in figure legend of Fig. 174 A.
307
T H E A R T A N D THE S C I E N C E OF C ATA R A C T S U R G E R Y
3. Combining the cataracttrabeculectomy into a single, unbroken incision
Instead of making the cataract portion of the incision at the limbus, the cataract incision is moved posteriorly to a position 1.5 mm or 2 mm posterior and parallel to the limbus. This is the preferred incision for extracapsular cataract surgery with trabeculectomy (Fig. 174).
A trabeculectomy block of 2 mm x 2 mm can be excised out of this scleralcorneal bevel (Figs. 179, 180) without the necessity of cutting a separate trabeculectomy flap in the sclera (Fig. 173). The end result is a trabeculectomy block dissected within the scleral cataract incision which is a simple, unbroken incision (Fig. 180) adding significantly to the stability of the scleral incision and reducing the amount of postoperative astigmatism.
B. Phacoemulsification with Trabeculectomy
This is presently the preferred technique for those with experience in phacoemulsification surgery. It results in the least level of postoperative astigmatism and rapid visual rehabilitation.
The most popular incision is similar to the one shown in Fig. 177 except that the pocket incision is made to a chord length between 3.1 mm and 6 mm rather than the 10 mm chord length incision used for extracapsular extraction. The chord length of this incision will depend on the size and type of intraocular lens used. Thus, for a foldable silicone or acrylic IOL, a 3.5 or 4 mm chord length will be used; whereas, for a PMMA
lens a 5.5 or 6 mm chord length incision would be used.
The trabeculectomy block is removed from the scleral bevel within the incision as described previously in Figs. 179, 180. (For details of the surgical technique see Phacoemulsification Cataract Incision with Trabeculectomy later in this chapter, Figs. 182, 187.
Intraocular Lens Implants
Luntz considers that the indications for implanting an intraocular lens are the same in glaucoma patients as in non-glau- coma patients. The posterior chamber intraocular lens is preferable. Anterior chamber lenses (Kelman-Multiflex - Editor) have been successfully used where a posterior chamber lens cannot be safely used, for example, where the anterior and posterior capsule have been extensively torn and will not support a posterior chamber intraocular lens in the bag or in the sulcus. (This subject is discussed in detail in pages 118-123 - Editor).
Preoperative Preparation
Pilocarpine drops should be stopped 24-48 hours before surgery in order to facilitate pupillary dilatation at the time of surgery. If preoperative intraocular pressure is high it should be reduced prior to surgery with intravenous Mannitol (1.5 g./kg. body weight) or with oral glycerine 75 cc. Topical steroids (Prednisolone 1% q.i.d.) and topical nonsteroidal antiinflammatory drops are given 24hours before surgery and continued for 1 to 2 weeks after surgery. This reduces postoperative inflammation and may diminish the incidence of cystoid macular edema.
308
C h a p t e r 12: Cataract Surger y in Complex Cases
Figure 175 A (right): Evolution of Types of Combined Cataract Extraction-Trabeculectomy - Type 4 - Tunnel Incision for Phacoemulsification and Trabeculectomy
A 1/2- scleral thickness, 6 mm cord length groove (S) is made 1.5 mm posterior to the limbus. A scleral tunnel (T) (its margins denoted by dotted lines) is dissected to the limbus. The corneal incision for introduction of the phacoemulsification probe and trabeculectomy window (W) are located within the resulting scleral bed. Iridectomy (I). Fornix based conjunctival flap.
Figure 175 B (left): Evolution of Types of Combined Cataract Extraction-Trab- eculectomy - Type 4 - Tunnel Incision for Phacoemulsification and Trabeculectomy - Section View
Compare this cross section view with the one shown in Fig. 174 B. The scleral tunnel flap is much smaller. The cataract incision (C) in Fig. 174 B is much larger. This figure shows in cross section what is described in the surgeon’s view in Fig. 175 A.
309
T H E A R T A N D THE S C I E N C E OF C ATA R A C T S U R G E R Y
SURGICAL TECHNIQUES STEP BY STEP
The following is a summary of the two main procedures step-by-step as recommended by Luntz.
ECCE and Trabeculectomy
With Single, Unbroken Tunnel
Incision
Conjunctival - Tenon’s Flap
(Fornix-based) (5x-7x Magnification)
If Mitomycin is to be used Luntz prefers to apply it to the conjunctival surface before raising the conjunctival-Tenon’s flap (see section on antimetabolites further in this chapter).
A superior rectus bridal suture is optional. The fornix-based conjunctival-Tenon’s flap with a 12 mm cord length is raised at the superior limbus. The flap is dissected posteriorly to further expose the sclera. Adequate hemostasis and clearing of the sclera is obtained.
Luntz considers that the fornix-based conjunctival flap has many advantages compared to a limbus-based flap:
1)There is better exposure and visualization of the operative field.
2)The possibility of damaging the conjunctival flap during dissection, particularly producing a «buttonhole» is eliminated.
3)A fornix-based flap is technically easier to dissect than a limbus-based flap, especially when operating in an area of scarred conjunctiva, either from previous surgery or trauma. It also offers better exposure of the surgical area.
4)The fornix-based conjunctiva flap adheres and scars at the limbus. As a result, the bleb forms posteriorly producing a diffuse, well-vascularized «low-profile» bleb well behind the limbus. There is less possibility of developing a thin «high-profile» avascular anterior bleb which overhangs the cornea, which has the added risk of microscopic perforations of hypoxic conjunctiva and possible intraocular infection.
5)The posteriorly situated bleb and the scar at the limbus allow safe and early contact lens fitting if a contact lens is required.
6)Tenon’s fascia is minimally trau-
matized.
Scleral-Corneal Incision
(7x-10x Magnification)
A 1/2-thickness scleral groove is cut in the exposed sclera using a diamond knife blade or a crescent knife blade 1.5 mm posterior to the surgical limbus, extending for 9.5 to 10 mm cord length parallel to the limbus (Fig. 176). At the center point of the incision (12:00 o’clock position) a crescent knife blade is used to dissect a scleral tunnel just anterior to the corneal vascular arcade which is then dissected to each side across the cord length of the incision (Fig. 176). A 3.1 mm keratome is introduced into the «tunnel» at 12 o’clock and advanced to the anterior limit of the tunnel in the cornea (Fig. 176). Pressing the point of the keratome downward toward the iris, the keratome is advanced and penetrates the cornea into the anterior chamber with the tip of the keratome 45º to the iris plane (Fig. 177). At this point, the direction of the keratome tip is changed to run parallel to the iris surface and the keratome is advanced fully into the anterior chamber to
310
C h a p t e r 12: Cataract Surger y in Complex Cases
Figure 176 (above): Combined Extracapsular Cataract Extraction - Trabeculectomy Procedure With Single, Unbroken Tunnel Incision - Steps 1 and 2
A 12 mm cord length, fornix based conjunctival flap (C) is reflected. A 1/2 thickness vertical scleral groove incision (S) is made with a diamond knife or crescent knife (not shown), 1.5 mm posterior to the limbus for a cord length of 9.5 to 10 mm, parallel to the limbus. At the center the groove (12 o’clock position), a crescent knife blade (K), is used to dissect a scleral tunnel to just anterior to the corneal vascular arcade. The sclera is then dissected to each side across the length of the groove (arrows - dotted lines).
complete the 3.1 mm incision (Fig. 177). The keratome is removed and the anterior chamber filled with viscoelastic. Using a Superblade, a paracentesis incision is made at the 9:00 o’clock and 3:00 o’clock meridians.
Figure 177 (below): Combined Extracapsular Cataract Extraction - Trabeculectomy Procedure With Single, Unbroken Tunnel Incision - Step 3
A 3.1 mm keratome (K) is introduced into the tunnel at the 12 o’clock position and advanced to the anterior limit of the tunnel in the cornea (inset - 1). The tip of the keratome is depressed and advanced into the anterior chamber. At this point, the direction of the keratome tip is changed to run parallel to the iris surface and the keratome is fully advanced into the anterior camber (inset -2 ) to complete the 3.1 mm incision. The keratome is removed and the anterior chamber is filled with viscoelastic.
311
T H E A R T A N D THE S C I E N C E OF C ATA R A C T S U R G E R Y
Anterior Capsulotomy
(10x Magnification)
A 27-gauge needle with the tip bent to 90º is introduced into the anterior chamber and a can-opener capsulotomy or preferably a large capsulorhexis, depending on the surgeon’s preference is performed.
Completion of Sclero-Corneal
Incision (10x Magnification)
The scleral flap is lifted and microsurgical corneal-scleral scissors are introduced into the scleral-corneal incision cutting to the left and right, completing the incision into the anterior chamber for the entire cord length of the original scleral groove (Fig. 178). The final result is a 9.5 to 10 mm cord length
incision into the anterior chamber with a 1.5 - 2 mm wide scleral-corneal bevel (Fig. 174).
Trabeculectomy
(10x Magnification)
The anterior chamber is filled with viscoelastic . A 2 mm x 2 mm block of tissue is excised from the scleral-corneal bevel at the 12:00 o’clock position using a LuntzDodick microsurgical punch (Katena). The posterior limit of the excised scleral-corneal block reaches to the scleral spur (Figs. 179, 180).
The trabeculectomy opening located in the center of the scleral-corneal incision reduces resistance of the scleral bevel to passage of the lens nucleus from the eye and facilitates its removal.
Figure 178: Combined Extracapsular Cataract Extraction - Trabeculectomy Procedure - Step 4
After an anterior capsulotomy or capsulorhexis has been performed, the scleral flap (F) is lifted and corneal-scleral scissors (D) are introduced into the previous 3.1 mm incision. The cataract incision is extended to the left and right (arrow) using the scissors. This produces a 9.5 to 10 mm cord length incision into the anterior chamber with a 2mm-wide scleral-corneal bevel. The anterior chamber is then filled with viscoelastic.
312
C h a p t e r 12: Cataract Surger y in Complex Cases
Figure 179 (left): Combined Extracapsular Cataract Extraction - Trabeculectomy Procedure - Step 5
This cross section shows the scleral-corneal bevel (T). An approximately 2 by 2mm block of tissue is excised from the scleral-corneal bevel
(T) at the 12 o’clock position using a Kelly Descemets punch (P) or Vannas scissors. The posterior limit of the excised block reaches to the scleral spur (arrow).
Figure 180 (right): Combined Extracapsular Cataract Extraction - Trabeculectomy Procedure - Step 6
This surgeon’s view shows the initial 1/2-thickness scleral groove incision (S), the completed 9.5 to 10mm scleral-corneal bevel incision (C), the approximately 2mm by 2mm trabeculectomy window (W) and reflected scleral flap (F). (See Figure 174 B for corresponding cross section view). The surgeon then performs an extracapsular cataract extraction and IOL insertion using his/her preferred technique. A peripheral iridectomy under the trabeculectomy is essential.
313