Ординатура / Офтальмология / Английские материалы / The Art of Phacoemulsification_Mehta, Alpar_2001
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THE ART OF PHACOEMULSIFICATION |
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bupivacaine HCl suggests that it causes undesired mucous production.) Intracameral anesthesia is achieved with unpreserved lidocaine HCl 1.0 percent. Some surgeons advocate diluting the intracameral agent with BSS solution in order to raise the pH and reduce the mild discomfort associated with anterior chamber instillation.
• Administer topical proparacaine HCl 0.4 percent to initiate anesthesia with little sting. Administer dilating agents (cyclopentolate or tropicamide and phenylephrine 2.5%), topical antibiotics, a topical NSAID, and lidocaine HCl 4.0 percent four times at five minute intervals prior to surgery.
•After the patient is brought into the theater several drops of the 4.0 percent lidocaine are administered prior to the sterile “prep”. The latter begins with instillation of two drops of half strength Betadine solution (not Betadine scrub) directly to the operative eye. At this time very small amounts of intravenous sedation may be given, depending upon the mental and medical status of the patient, the anxiety of the surgeon, and the observations of the anesthetist or equivalent. The author generally asks that 0.5 mg to 1.0 mg of midazolam HCl be administered IV.
•During the draping process communicate with the patients about the operative process. Tell them that they will feel slight pressure from the lid speculum and that they will need to fixate on the light of the microscope. Tell them that requests to look up, down, etc. should be achieved by moving the eye and not the head. Reassure them that they will feel no pain.
•Begin surgery with the microscope light at low levels of illumination, sufficient only to perform a paracentesis. Place 0.2 cc of non-preserved lidocaine HCl in the anterior chamber and follow that with the viscoelastic of choice. The anesthetic will be washed out as the viscoagent fills the chamber if the lip of the sideport is depressed as the viscoelastic is injected. Slowly increase the microscope light and perform the clear-corneal incision. Continue with routine surgical procedure.
•Generally, no further anesthesia is necessary. However, in situations with prolonged surgery or very sensitive patients, additional intracameral anesthetic may be administered for complaints of “pressure“ or intraocular pain. For surface discomfort the conjunctiva may be swabbed with a pledget of any sterile topical anesthetic, but care should be taken to avoid placing the agent near or in the incision if it contains preservatives. Additionally, small increments of intravenous sedation can be added as may be (rarely) necessary.
•In the very unlikely case that the patient cannot tolerate the microscope light even at low illumination and continues to squeeze the lids against the speculum, additional doses of IV medicine could be given until the intracameral anesthetic is administered. In the author’s observations, once the eye has received the intracameral agent, all lid squeezing and signs of anxiety or discomfort abate rapidly. However, in extreme situations or should an operative complication occur that will significantly prolong surgery, one can stop surgery, given a self-sealing incision, pressurize the eye to normal, and administer deep sub-Tenon’s local anesthetic with a blunt cannula (Fig. 6.1) through a conjunctival buttonhole entry in the superior or inferior nasal quadrant.
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Prior to incising the conjunctiva, a pledget of local anesthesia may be placed on the area for a few moments. The cannula should reach the retrobulbar space with ease if the buttonhole opening includes Tenon’s capsule. Only 2.0 cc of local agent is necessary, given direct access to the muscle cone. Relative amaurosis will be achieved in a matter of seconds, and, with strong local agents, akinesia can be established in a few minutes.
REFERENCES
1.Leaming DV: Practice styles and preferences of ASCRS members—1996 survey. J Cataract Refract Surg 23:527-35, 1997.
2.Cionni R, Osher R: Retrobulbar hemorrhage. Ophthalmology 98:1153-55, 1991.
3.Duker JS, Belmont, JB, Benson WE et al: Inadvertent globe perforation during retrobulbar and peribulbar anesthesia. Ophthalmology 98:519-26, 1997.
4.Hay A, Flynn Jr HW, Hoffmann JI et al:. Needle penetration of the globe during retrobulbar and peribulbar injections. Ophthalmology 98:1017-24,1991.
5.Grizzard WS, Kirk NM, Pavan PR et al: Perforating ocular injuries caused by anesthesia personnel.
Ophthalmology 98:1011-16, 1991.
6.Masket S, Tennen DG: Astigmatic stabilization of 3.0 mm temporal clear corneal cataract incisions.
J Cataract Refract Surg, 22(10):1451-55, 1996.
7.Fine IH, Fichman RA, Grabow HR: Clear-corneal Cataract Surgery and Topical Anesthesia. Slack Inc: Thorofare, 1993.
8.Gills JP, Cherchio M, Raanan MG: Unpreserved lidocaine to control discomfort during cataract surgery using topical anesthesia. J Cataract Refract Surg 23:545-50, 1997.
9.Koch PS: Anterior chamber irrigation with unpreserved lidocaine 1% for anesthesia during cataract surgery. J Cataract Refract Surg 23:551-54, 1997.
10.Masket S, Gokmen F: Efficacy and apparent safety of intracameral lidocaine as a supplement to topical anesthesia. J Cataract Refract Surg (24)7:956-60, 1997.
11.Stevens JD : A new local anaesthesia technique for cataract extraction by one quadrant sub-Tenon’s infiltration. Br J Ophthalmol 76:670, 1992.
12.Greenbaum S: Anesthesia in cataract surgery. In Greenbaum S (Ed): Ocular Anesthesia WB Saunders: Philadelphia 1-55, 1997.
13.Fukasaku H, Marron JA: Pinpoint anesthesia—a new approach to local ocular anesthesia. J Cataract Refract Surg 20:468, 1994.
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THE ART OF PHACOEMULSIFICATION
Shashi Kapoor
The limbal Incision |
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I N T R O D U C T I O N
Kratz is credited as the first surgeon, to move from the limbus posteriorly to the sclera, increasing appositional surfaces to enhance wound healing and attempt to exert less traction on the cornea, thereby controlling surgically induced astigmatism. Girard and Hoffmann were the first to call the posterior incision a “scleral tunnel” incision. In 1989, McFarland and Ernst introduced an incision architecture that allowed the phacoemulsification and implantation of lenses without the need for suturing. Besides lengthening the scleral tunnel, this incision terminated in a decidedly corneal entrance and the posterior lip of the incision, the so-called corneal lip, acted as one-way valve imparting to this incision its self-sealing characteristics. Paul Koch described what he called the `incision funnel’ indicating that there were certain characteristics of self-sealing incisions with respect to length and configuration that imparted not only self-sealability but also astigmatism neutrality to these incisions. The advent of the foldable IOL and advances in device technologies have led to significant refinements in small incision surgery and wound closure that are revolutionizing the practice of cataract surgery. These clinical advances are leading to reductions in iatrogenic ocular trauma and postoperative astigmatism, decreased risk of hyphema, delayed filtering blebs and iris prolapse, increased wound stability, and faster recovery and vision restoration.
Posterior Limbal Incision
Ernst et al are advocating the use of the temporal posterior limbal incision, which can be made nearly square for foldable IOLs (3.2 mm × 3.0 mm). In a cadaver
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Fig. 7.2: Square corneal wound, 2 × 2 mm (1.5 mm being the minimal internal corneal lip) is impractical, as it is too small to permit the insertion of current phaco tips and IOLs
Fig. 7.1: Square corneal wound, 3.5 × 3.5 mm, is impractical since it impinges on the visual axis, and causes disturbing striae, intraoperatively
eye studies, as rectangular clear corneal incisions were made more square by only 0.5 mm from 3.2 mm × 2.0 mm to 3.0 mm × 2.5 mm, they became more resistant to pressure. Once the length was increased so that the wounds were square (3.2 mm × 3.2 mm) with a 1.5 mm internal corneal lip, they were capable of withstanding maximal external pressures of 525 psi. As yet, square clear corneal incisions are clinically impractical, because they either encroach upon the visual axis (Fig. 7.1) or are too small to permit the insertion of current phaco tips and IOLs (Fig. 7.2).
The limbal incision has several advantages over the currently advocated clear corneal incision. Clear corneal incisions, especially those that have a vertical component, are more subject to foreign body sensation than limbal incisions. This irritation occurs because there is edema of both the anterior and posterior aspects of the incision in clear corneal incisions with vertical components, which creates a gape in the most superficial aspect of the incision (Figs 7.3A and B). In turn, this gape forms a ridge that can irritate the patient.
Dr Tipperman et al, performed a feline study evaluating limbal versus clear corneal incisions. The incision dimensions were non-square, 3.00 mm in width and 1.75 mm in length. A paracentesis type incision was made in each case. Reformation of the anterior chamber and stromal hydration were not performed.
The eyes were observed over a period of 16 days. Pinpoint pressure was applied to each eye at various time intervals. The results showed a statistically significant
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Fig. 7.3A: Schematic drawing of a clear corneal incision postphacoemulsification showing corneal edema and ridge
Fig. 7.3B: Schematic diagram of a limbal incision postphacoemulsification showing edema of the corneal tunnel, but not edema of the incision
difference in resistance to pinpoint deformation pressure between the limbal and paracentesis incision (P = 0.0034) (Fig. 7.4).
Incision Design
The design of modern sutureless, self-sealing cataract incisions, involves the consideration of three design parameters, site, size and shape.
Incision Shape
Shape is an anatomic parameter in the geometric consideration of cataract incision construction. There are two aspect views of these incisions: sagittal and anteroposterior; and three components: the external incisions, the intratissue tunnel and the internal incision. From the sagittal aspect, limbal incisions may be made in one of following configurations varying, between single-plane, grooved beveled and triplane with a groove and a bevel.
The external component of limbal incisions also may be in one of the following theoretical configurations: the single-step “stab” incision as initially introduced by Howard Fine; the two-step grooved incision by Charles Williamson, who felt that the incision should be larger on the outside than the inside, which would allow the injector to fit more easily in the incision without stretching the sclera.
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Fig. 7.4: Graph comparing resistance deformation pressure of clear corneal (CC) and limbal incisions (LB) over time
The ultimate goal is to have no tissue stretch. The trapezoid incision that Dr Williamson describes are about 0.5 mm wider on the outside than the inside.
Langerman Hinge and Gills Modification
Langerman and Gills have modified clear corneal incisions, and these modifications are applicable to limbal incisions.
Although clear corneal incisions appear to be watertight at the end of surgery, Langerman and Ernst have shown that both the straight-in and two-plane clear corneals can leak. This ability to leak indicates a less than perfect seal. John has shown a higher incidence of sterile endophthalmitis in clear corneals compared to scleral tunnels. This increased incidence is probably due to reflux of flora into the anterior chamber through the incision. The lack of culture positive infection can be attributed to John’s aggressive prophylactic antibiotic regimen, after the Gills method.
Langerman has developed a hinge technique which involves making the initial vertical groove deeper than the point at which the horizontal shelf is started (Fig. 7.5). The deep groove then functions as a hinge, with the inner aspect of the incision flexible and malleable, allowing it to adhere to the outer portion of the incision.
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The Gills modification of the Langerman hinge involves a vertical incision that is 85% deep. The next step is to create a deep longitudinal bevel in the stroma in either a single-or twoplane fashion. This portion is deeper and longer than Langerman describes.
Because the inner flap is very thin, it allows for greater flexibility and better contact when pressure is applied to any portion of the wound.
The key to creating a very deep, thin incision is to pick up the distal aspect
of the limbal wound with forceps. This step is essential for two reasons: (i) it allows the surgeon to have control over fixation of the eye when using topical anesthesia, and (ii) it allows the surgeon to make a deep incision with greater ease. The flap is created by directing the keratome (diamond or metal) toward the dome of the eye. After tunneling through the posterior stroma for a distance of approximately two-thirds the keratome width, the incision is beveled posteriorly through Descemet’s membrane and into the anterior chamber. Using a 2.3 mm to 2.5 mm trapezoidal keratome and beveling it into the anterior chamber approximately 2 mm will create a 2.3 mm to 2.5 mm by 2.0 mm incision. The incision performs similarly to navigational valves, when pressure against the rubber forces the aperture closed.
Grooved incisions provide a superficial corneal flap that has a thicker edge, which helps to avoid avulsion when grasping with forceps or when suturing. The deep groove of Langerman is believed to physically separate the sclera from the internal corneal flap sufficiently to allow sclera indentation (patient rubbing) without internal wound separation, thereby reducing the potential for wound leak.
The sagittal shape and direction of the tunnel may also vary. Most tunnels are made flat or planar by flat blades advanced in a single plane. Some surgeons
believe there may be superior |
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sealability with a convex sagittal |
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curve to the tunnel although it is |
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technically difficult to create and to |
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reproduce. |
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The third component of these |
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incisions, the internal opening, may |
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have one of two sagittal shapes: |
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single-plane “stabs” in the same plane |
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as the limbocorneal tunnel (Fig. 7.6), |
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or bi-planar “steeped”. In addition, |
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Singer proposes that the most |
Fig. 7.6: Limbocorneal tunnel incision |
accurate anatomic angle of entry into |
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Figs 7.7A to C: Anteroposterior aspect of limbaltunnel (Grabow): (A) convergent trapezoid, (B) parallelogram, and (C) divergent trapezoid
the anterior chamber through the endothelial surface is 17.5 degrees, that which duplicates the average angle of perforation of scleral veins.
The anteroposterior aspect of the second component of limbal incisions, the tissue tunnel, is summarized in Figures 7.7A to C. The original configuration was parallelogram introduced by Fine. The second configuration, was a convergent trapezoid, introduced by Williamson. In this design, the external incision is longer than the internal incision, to improve instrument maneuverability while preserving the smallest internal opening for self-sealability. The third configuration, the divergent trapezoid of Hoffer, has its external opening smaller than its internal opening, to reduce the astigmatic effect, while allowing maneuverability internally.
The anteroposterior aspect of the third incisional component, the internal opening has only recently come under investigation. Three directional possibilities exist for this incision (Figs 7.8A to C): limbus-parallel, tangential and limbus-antiparallel (“corneal frown”).
Limbus-parallel internal incisions, unlike limbus parallel external incisions, have been demonstrated to be the most stable and most resistant to deformation and leakage. Conversely, corneal frown internal incisions are the weakest.
Therefore, cutting strokes to enlarge an internal incision should move either in a central direction, by advancing the blade, or in a lateral direction, so as to preserve a limbus-parallel configuration, rather than in a peripheral direction, as when withdrawing the blade.
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Figs 7.8A to C: Anteroposterior aspect of internal corneal openings (Grabow): (A) limbus parallel, (B) tangential, and (C) limbusantiparallel “corneal frown”
Site
One classification of location of cataract incisions, involves the radial distance from the optic axis. These locations for cataract incisions have traditionally been designated by their anatomic locations; the sclera, the cornea, and the junction of these two—the limbus.
Scleral Incisions
Scleral incisions, being furthest from the optic axis, when compared to corneal and limbal incisions of equal dimension, have less effect on both corneal astigmatism and the corneal endothelium, and the same is true for peripheral corneal incision as compared to more central corneal incisions.
The external entry incision for small, self-sealing sclerocorneal incisions, as originally described was made 3 to 4 mm posterior to the limbus. The distance from the limbus has become progressively less as surgeons have become more conversant with creating the self-sealing internal corneal lip. Now most surgeons are comfortable about 1.5 mm posterior to the limbus, giving a total sclerocorneal tunnel length of approximately 2.5 to 3.0 mm. In 1972, Fine introduced the clear corneal incision, which was originally described as a stab incision temporally located in avascular tissue. Since then, many modifications and variations have been developed, encompassing a wide variety of sutureless incisions.
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Limbal Incision
Anatomists describe the anterior vascular arcade as extending 0.5 mm into clear cornea, anterior to the limbus with its external surface covered by conjunctiva.
Thus the limbus can be defined as the anterior edge of the conjunctival insertion, with the corneal vascular arcade considered to be in clear cornea.
Architecturally, limbal incisions can be described as follows.
a. Single plane (without a vertical groove at the external edge of the incision) b. Shallow groove (having a groove perpendicular to the corneal surface at 
the external edge of the incision, upto 400 µ deep)
c.Deeply grooved (where the groove perpendicular to the external edge of the incision is greater than 400 µm).
In another classification, the cataract incision is usually described as located at one of four possible sites on the corneal circle superiorly, obliquely, temporally or on steep axis. Superiorly located incisions when not under the influence of sutures, are known to have an against-the-rule (ART) astigmatic effect, greater with longer incisions, due to the effects of gravity and/or lid closure on wound gape.
The oblique location, whether nasal or temporal, is espoused by some who prefer this site not only for ergonomic advantage, but also for greater wound stability when compared to superior incisions. These wounds are believed by some to be the only ones not affected by transmitted tractional forces of a rectus muscle, a theory yet to be documented.
Superolateral Incisions
It has been reported that a lateral or superolateral incision, can decrease and quickly stabilize surgically induced astigmatism (SIA), although the reason for this is unclear. Hayashi et al compared superior (group I) with superolateral incisions (Group 2) in IOL patients who underwent a 6.5 mm beveled incision, 0.5 mm posterior to the surgical limbus, followed by endocapsular phacoemulsification, enlargement of incision to 6.5 mm and insertion of a posterior chamber IOL with a 6.0 mm optic. The wound was closed by 3 interrupted 10-0 nylon sutures. The patients were followed up using keratometer and computerized corneal topography.
Figure 7.9 shows the induced changes in the mean keratometric cylinder at each interval, in the two groups. Group 1 has significantly less induced astigmatism throughout the six month follow-up than group 2. The patients in group 1 also had less standard deviation throughout the follow-up than the patients in group 2. This indicates that SIA in group 1 was less variable than in group 2.
Two types of corneal topographic maps were used to illustrate the postoperative corneal shape alterations: color-coded maps “averaging” all corneas at each interval and absolute scale maps of individual cases. The averaged maps of Group 1 patients show a slight steepening in the central cornea in the 10 O’clock meridian, one week after surgery. There were no remarkable changes in the peripheral cornea. The surgically induced steepening in the central cornea disappeared within one