Scleral stretch incision for cataract surgery

Scleral stretch incision for cataract surgery A technique for no-suture closure and control of astigmatism Jerre Minor Freeman , M. D .

8 TR T The . c1eral h'ctch in i ion fOI' cataract 'urg r b phac emul ification i. a three-plane multi, idth corneal inci i n. It i. a refin mcnt of the c1 ral pock t inci ion, It u the ela ticity of leral ti ue for in rti n of a tandard (6.0 mm ) pol (meth I methacr late) intrao ular len (I )through a mall r (4 .5 mm) in i ion. Th te hniqu al 0 al1O\ pont n ou wound c10 UI' , ithout a utur. d ant e of the c1 ral tr t h inci ion t hniqu are an efficient, \ ate rtight entr into th e e ~ r pha oemul ification and I L in ertion and no- utUl' 10 ur. arl c1ini al ob er at ion indicat that th c1eral tr tch in i ion minimiz ur i all induced omeal a tigmati m. K y \Vord : corn ':II astigmati"m, 1l0-'>lIture <:Io"lIr' , ph:lC:o ·ll1ul..in'ation , sdentl st r ,tch in 'ision , ,>mall-inc:isioll ·atara·t Sllrgt' r~

The current focus of cataract research is on the natural course of corneal astigmatism follOWing surgery and its control. l The type and length of incision and technique for wound closure influence surgically induced corneal astigmatism. 2-4 Because longer incisions are associated with increased corneal flattening, the trend in cataract surgery is to minimize incision length and the consequent number of sutures to close the incision. The scleral stretch incision for cataract surgery by phacoemulsification is a multiplane, multiwidth corneal incision that I developed as a refinement of the scleral pocket, or scleral tunnel, incision. It uses the elasticity of scleral tissue for the insertion of a standard (6.0 mm) poly(me thyl methacrylate) (PMMA) intraocular le ns (IOL) through a 4.5 mm incision. The scleral stretch incision allows spontaneous wound closure without a suture in most patie nts. Although this incision is technically com-

plex,5 it can be broken down into simple components. Advantages toboth surgeon and patient are an efficient, watertight entry into the eye, no-suture closure, and minimization of surgically induced astigmatism. TECHNIQUE A standard winged, fornix-based conjunctival flap is made and turned superiorly from 11 o'clock to 1 o'clock, exposing a scleral area approximately 6 by 5 mm . The exposed sclera is lightly cauterized . Calipers are set at 4.5 mm for a standard 6.0 mm PMMA IOL (3.6 mm for a 5.0 mm IOL, 5.4 mm for a 7.0 mm IOL). Two end points are marked at or near 12 o'clock on the superior sclera and 3.0 mm to 3.5 mm posterior to the center of the peripheral corneal vessels (Figure 1). With a sharp steel or diamond blade , aslight curvilinear incision is made,

Presented in part at the Symposium on Cataract , IOL and Refractive Surgery, Boston , April 1991. Joseph F. Weiss, M.D., Thomas C. Gettelfinger, M.D., Joseph M. Scott, M.D., Emily Hayes, Suzanne LaRue, C.o.T, and Noel Dawn Carpenter, C.o.A., reviewed the manuscript and Barbara J. Kuyper, Ph.D. , University of Tennessee, Memphis, proVided editorial assistance. Bryon Wood provided all illustrations. Reprint requests to Jerre Minor Freeman, M.D ., MECA, 6485 Poplar Avenue, Memphis , Tennessee 38119. 696

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Fig. 1.

(Freeman) The first two steps of the scleral stretch incision. Starting 3.0 to 3.5 mm posterior to the midpoint of the peripheral corneal vessels, the initial, curvilinear scleral incision is made at a depth of 350 J.Lm to 400 J.Lm from point 1 to point 2 (4.5 mm). With a round pocket blade, the peripheral cornea is dissected to the midpoint or edge of the peripheral corneal vessels and then right and left past points 1 and 2 to enlarge the internal width to 6.5 mm.

curving forward between the two end points and aiming at a depth of 350 /-Lm to 400 /-Lm. This depth, or flap, should be 60% to 70% of scleral thickness. (Recently, I have been using a single-sided, guarded diamond knife for greater accuracy of depth.) With a small pocket blade (Grieshaber or Beaver), the peripheral clear cornea is dissected to the anterior ~dg~ of the peripheral corneal yessels. The pocket

Fig. 2.

blade is used to dissect right and left past the end points of the original incision for l.0 mm to l.5 mm on either side (a unique feature of this incision). The blunt part of the blade where it joins the handle is bumped or pushed against the ends of the incision. A 3.2 mm keratome is passed through the righthand side of this incision (for a right-handed surgeon) into the anterior chamber (Figure 2, left). This step is difficult because the sharp point of the keratome can catch on the scleral lamellae during its slide forward. The point of the keratome is placed high within the dissected pocket or tunnel before it is pushed through the thin, internal wall into the anterior chamber, making sure that the point is anterior to Schwalbe's line but not as far anterior as the tunnel or pocket (Figure 2, right). This procedure creates a three-plane, multiwidth incision (Figure 3). Either before or after the anterior chamber entry with the keratome, an additional, small, separate anterior scleral or clear corneal paracentesis is made at approximately 1 o'clock just to the left of the scleral stretch incision, staying outside of and not communicating with the intrascleral space, or cavity, of the scleral stretch incision (Figure 4). This tiny, side-port incision is used to insert the Binkhorst spatula, which is a critical aspect of bimanual phacoemulsification technique. 6, 7 Phacoemulsification is performed through the scleral stretch incision. The advantage of initially constructing the incision wide enough to accept the IOL, leaving only the final entry into the anterior chamber to be enlarged, now becomes apparent. The external sclera is allowed to elevate, thus

(Freeman) Left: Initial entry into the anterior chamber. A 3.2 mm keratome is passed forward to engage the internal wall of the dissection about 20% to 25% short ofthe full anterior dissection. As the point of the keratome passes into clear cornea and into the anterior chamber, the point is dropped toward the pupillary plane and the entry is completed. Right: Anterior chamber view of the initial entry. Note the point of the keratome emerging through the internal wall anterior to Schwalbe's line, creating the internal flap.

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Fig. 3.

(Freeman) Side view of the multiplane incision . The initial entry (1), 350 j.Lm to 400 j.Lm deep, or 60% to 70% of scleral thickness. Lamellar dissection (2) carried forward to the anterior edge of the peripheral corneal vessels. Anterior chamber entry (3) through the thin inner wall .

transmitting less distortion to the corneal surface. The internal wall of the scleral stretch incision apparently moves back and forth as the phacoemulsifier moves, and this wall movement appears to reduce the transmission of direct forces to the corneal surface, thereby reducing distortion (Figure 5). This is especially important in the deep moves and work required for posterior chamber and in-the-bag phacoemulsification. After completing phacoemulsification, a small amount of viscoelastic material is placed within the incision. A modified, blunt-tip keratome is passed into the original keratome incision (MECA blunt-tip keratome manufactured-modified by Rx Honing

Flaps Move With Phaco, Minimizing Corneal Distortion

Fig. 5.

698

(Freeman) Move ment of the inner wall during phacoemulsification.

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Fig. 4.

(Freeman) Paracentesis. With a small knife-needle, a straight-through incision is made in the anterior sclera or peripheral cornea at 1 o'clock just to the left and outside of the scleral stretch incision, making sure not to connect with intrascleral space .

Machine Corporation, Mishawaka, IN). The use of a blunt-tip keratome at this point avoids creating a second, separate anterior chamber entry. The blunt tip is swiveled right and left, and the internal anterior chamber entry is widened with gentle, short cutting action to approximately 6.5 mm (5.5 mm for a 5.0 mm IOL, 7.5 mm for a 7.0 mm IOL) (Figure 6). More viscoelastic is placed in the anterior chamber and within the incision. The 6.0 mm PMMA IOL is slowly inserted through the 4.5 mm initial entry and then passed through the rest of the incision into the anterior and posterior chambers (Figure 7). Again, the flexible internal wall of the incision allows for easier intraocular maneuvers and lens placement in the capsular bag. While developing and refining the scleral stretch incision for standard PM MA IOLs, I have found that the newer foldable IOLs can go through even smaller scleral stretch incisions without the use of special inserters. The pupil is constricted. Most of the viscoelastic material is removed and the anterior chamber is deepened through the small side-port incision at 1 o c' lock (Figure 8). Using the second, separate incision encourages the scleral stretch incision to close spontaneously without the aid of a suture in most patients. If mechanical wound closure is required, a single horizontal 9-0 nylon suture is usually sufficient. I leave the intraocular pressure (lOP) slightly elevated, from 18 mm Hg to 25 mm Hg, to tamponade and keep the internal flap of the incision snugly against the outer portion of the incision. The conjunctival flap is brought back across the incision and held in place with cautery along the right-hand side at 11 o'clock.

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Fig. 6.

(Freeman) Enlargement of the anterior chamber entry. Left: With a special blunt-tip keratome, the anterior chamber opening is enlarged to 6.5 to 7.0 mm by swiveling right and left with gentle, short cutting action. The small zone of blind passage anterior to the anterior chamber entry acts like a flap to allow greater freedom of movement of the phacoemulsifier tip with less corneal distortion. Right: Anterior chamber view of the enlargement.

DISCUSSION Many cataract surgeons prefer the standard PMMA IOL but would also like to take advantage of the smaller incision possible with foldable IOLs. The scleral stretch incision is one solution to this dilemma. The elasticity of the sclera allows the 6.0 mm PMMA IOL to be inserted through the smaller 4.5 mm entry. The curvilinear portion, or aspect, of the scleral stretch incision can be replaced with a straight incision, which is easier to make. But since the curvilinear measurement is slightly longer than the

chord length of the straight incision, it may allow the sclera to stretch farther. This curvilinear incision is a modification of the frown incision developed by Singer. s The internal flap functions like a hinge. The base of the hinge is the internal scleral ring and ciliary body. When the vitreous cavity is decompressed, the support to the hinge is altered. In three patients who had vitreous loss and subsequent vitrectomy followed by IOL placement in the posterior chamber, the internal flap would not close spontaneously upon filling the anterior chamber through the sideport incision. In· these three patients, a single

Increase lOP To 18·25 mm Hg

Fig. 7.

(Freeman) Insertion of the IOL. The 4.5 mm entry of the scleral stretch incision allows easy passage of the firm, 6.0 mm PMMA IOL. The entry may have to be enlarged slightly (0.1 to 0.2 mm) for IOLs of higher dioptric power.

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Fig. 8.

ealing Zone (Overrap Of Internal Flap & External Flap)

(Freeman) Incision closure. Balanced salt solution is slowly injected through the paracentesis until the eye is firm at a level of 18 mm Hg to 25 mm Hg. The internal flap closes more easily when fluid is injected from another site. It is normal to have a slight incision gape.

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horizontal nylon suture was placed for internal flap apposition and closure. Certain steps of the scleral stretch incision are critical. The external incision and the wider intrascleral lamellar dissection are relatively easy to learn. Much more difficult to master is locating the optimal point at which to enter the anterior chamber through the thin inner wall. An entry that is too high will result in increased distortion during phacoemulsification. If the entry is too low, the internal flap will not be long enough to close snugly without a suture. Although it initially seemed undesirable to make an anterior dissection or blind passage of the incision and then not use it, the anterior dissection probably has an advantage. It apparently allows more lateral, back-and-forth, up-and-down movement of the ph acoemulsifier tip without total transmission of these distorting forces to the critical optical surface of the cornea. The internal wall of this incision may act independently of the external sclera and co~neal surface, which in effect partially isolates certain distorting forces. Under normal or slightly high lOP, the incision will close snugly if there is an overlap of l.5 mm to 2.0 mm between the anterior aspect of the scleral incision and the posterior aspect of the anterior chamber incision. On occasion, the scleral flap thins, tears, or distorts, and closure is not secure. A suture is then required. In four patients who had postoperative wound leak, I sutured two incisions and allowed two to close spontaneously. Complications associated with the scleral stretch incision are those attendant to any modification of the scleral tunnel incision. Because the incision is smaller, the scleral and internal corneal tissues are subject to extra stretching and distorting forces. The incidence of early postoperative hyphema may be slightly higher. Since the smaller incision normally requires less external cautery, fresh, uncauterized vessels that bleed briskly are at times encountered when the internal corneal entry is enlarged. IfIOP at the end of surgery does not exceed capillary pressure either permanently or transiently, these small vessels may bleed. This problem should be approached cautiously. A possible solution is to use wider external cautery. I feel that no cataract incision is astigmatically neutral. However, the scleral stretch incision appears to minimize surgically induced astigmatism. In clinical observations, an against-the-rule astigmatic shift is evident almost immediately during the early postoperative period. Six-week data for 120 conSeCtltive cataract patients (January to May 1991) who had scleral stretch incisions with no-suture closure but who did not have relaxing keratotomy incisions 700

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support these clinical observations. All 120 patients had routine six-week postoperative refractive examinations. The average change, or decay, of the keratometric readings was -0.06 diopter (D) toward against-the-rule astigmatism. Refractive cylinder changes showed an average decay of -0.03 D toward against-the-rule astigmatism. Of the 120 patients, 101 had changes within l.00 D above or below their original keratometric readings, 17 had changes within l.12 D to 2.00 D, and 2 had changes greater than 2.00 D. These preliminary data may be misleading, however, because they represent a consecutive pool of patients who had either spherical corneas or mild to moderate with-the-rule astigmatism, which does not appear to decay as much with a surgical incision as against-the-rule astigmatism. Based on clinical observations during 1990, I concluded that there was a mild slippage of -0.50 D to -0.75 D toward againstthe-rule astigmatism. This perceived slippage, when added to the mild to moderate against-therule astigmatism existing in most elderly cataract patients, had an additive effect. Consequently, I was doing far peripheral relaxing keratotomy tangential incisions (T cuts) in most patients. Without the distorting effects of a suture used for closure, most of the astigmatic shift is due to wound or incision relaxation. Thus the scleral stretch incision may remove one of the variables that affect corneal ;lstigmatism. Reducing the number of variables causing the astigmatism also reduces the effort necessary to solve the problem. Since the scleral stretch incision has consistently resulted in a small amount of immediate and apparently stable againstthe-rule astigmatism, I am making corneal T cuts or astigmatic keratotomy incisions more frequently to promote a spherical cornea. Even without the addition of corneal T cuts, the incidence of early, good visual acuities without correction has been relatively high. CONCLUSIONS Cataract surgeons have known for over a century that the incision for cataract surgery induces astigmatism. Both clinically and experimentally, a smaller incision that approaches 3 mm in width induces the least amount of astigmatism. 2 - 4 In my surgical experience, the scleral stretch incision combines the advantages of both small and large incisions. I believe that extending the internal dimensions of the incision induces less astigmatism than extending the external dimensions. REFERENCES 1. Talamo JH, Stark WJ, Gottsch JD, et al. Natural history of corneal astigmatism after cataract surgery. J Cataract Refract Surg 1991; 17:313-318

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2. Armeniades CD, Boriek A, Knolle GE Jr. Effect of incision length, location, and shape on local corneoscleral deformation during cataract surgery. J Cataract Refract Surg 1990; 16:83-87 3. Samuelson SW, Koch DD, Kuglen CC. Determination of maximal incision length for true small-incision surgery. Ophthalmic Surg 1991; 22:204-207 4. Steinert RF, Brint SF, White SM, Fine IH. Astigmatism after small incision cataract surgery: a prospective, randomized, multicenter comparison of 4- and 6.5-mm incisions. Ophthalmology 1991; 98:417-424 5. Eisner G. Eye Surgery. An Introduction to Operative

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Technique, 2nd ed. Berlin, Springer-Verlag, 1990; 162 6. Freeman JM, Devine TM. Special considerations. Small pupil phacoemulsification. In: Devine TM, Banko W, eds, Phacoemulsification Surgery. New York, Pergamon Press, 1991; 87-99 7. Gimbel HY. Divide and conquer nucleofractis phacoemulsification: development and variations. J Cataract Refract Surg 1991; 17:281-291 8. Singer JA. Frown incision for minimizing induced astigmatism after small incision cataract surgery with rigid optic intraocular lens implantation. J Cataract Refract Surg 1991; 17:677-688

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