Ординатура / Офтальмология / Английские материалы / The Art of Phacoemulsification_Mehta, Alpar_2001

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widen the pupil, there is little likelihood of tearing the sphincter and allowing prostaglandins to leak out and cause inflammation or cystoid macular edema (CME). In this technique we can easily go into even hard nuclei on the first attempt.

Soft Cataracts

In soft cataracts, the technique is a bit different. We embed the phaco tip and then cut the nucleus as if we are cutting a piece of cake. This should be done 2 to 3 times in the same area so that the cataract gets cut. It is very tough to chop a soft cataract, so this technique helps in splitting the cataract.

Topical Anesthesia Cataract Surgery

All our cases are done under topical

Fig. 8.14: Stromal hydration anesthesia. Four percent Xylocaine drops are instilled in the eye about 3 time’s 10

to15 minutes before surgery. No intracameral anesthesia is used. It is not advisable to use Xylocaine drops while operating. This can damage the epithelium and create more trouble in visualization. No stitches and no pad are applied. This is called the—no injection, no stitch, no pad cataract surgery technique.

No Anesthesia Cataract Surgery

We had been wondering whether any topical anesthesia is required or not. So we then operated patients without any anesthesia. In these patients no Xylocaine drops were instilled. The patients did not have any pain. It sounds funny because we have been taught from the beginning that we should apply Xylocaine. This is possible because we do not touch the conjunctiva or sclera. We never use any one-tooth forceps to stabilize the eye. Instead what we use is a straight rod which is passed inside the eye to stabilize it when we are performing rhexis, etc. The anterior chamber should be well maintained and the amount of ultrasound power used very less. If you tend to use the techniques like trenching then the ultrasound power generated is high, which in turn generates heat. This causes pain to the patient. If you follow these rules one can perform No Anesthesia Cataract Surgery. It is not necessary to do this, as there is no harm in instilling some drops of Xylocaine in the eye. The point is that there is always a discussion

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which anesthetic drop to use. It does not matter. The technique, which you perform, should not produce pain to the patient.

C O N C L U S I O N

As in any other field, progress is inevitable in ophthalmology more so in cataract surgery. We have started to look on cataract surgery as a craft and should constantly try to improve our craft and become better everyday. By this, we will be able

to provide good vision to more people than any one dared dream a few decades ago. It also goes without saying that we are and will be forever grateful to

all our patients because without their faith, we would never have had the courage to proceed.

Keeping this in mind, we hope and wish that the effectiveness and the advantages of this “Karate Chop Technique” be realized and practised, thereby making the technique of phacoemulsification safer and easier providing good visual outcome and patient recovery.

86 THE ART OF PHACOEMULSIFICATION

Keiki R Mehta

Cyres K Mehta

INTRODUCTION

Clear corneal cataract incisions are becoming very popular for cataract extraction and IOL implantation throughout the world. Using clear corneal incisions, with the concomitantuseofintracameralanesthesia,cataractsurgeryhasnowbeenrefinedtosuch an extraordinary level, that it has reached the stage of virtually immediate, visual rehabilitation.Perhapsthegreatestadvantageofclearcornealincisionsisthetremendous safety with relative astigmatic neutrality, coupled with exceptional results.

The limbal location for cataract surgery has been in use from time immemorial. In India, couching has been an established technique, which, is still in use in inaccessible parts. Jaques Daviel in 1745 utilized clear corneal incisions in his cataract surgery technique. Albrecht Von Graefe in 1750 developed a clear corneal knife and developed a very successful corneal incision technique that became famous as the “Graefe section”. Kratz in 1980, was the first phacoemulsification surgeon to go more posterior , making scleral incisions commencing far back and tunneling forwards with a view to increase appositional surface, which would enhance wound healing and thus reduce surgically induced astigmatism.

Gerard and Hoffman in 1984 were the first to name the posterior incision as “the corneal tunnel”. Moreover, they were the first to make a point of entering the anterior chamber through the cornea, creating for the first time a corneal shelf. Maloney in 1988, popularized this particular corneal shelf, which in the earlier days was made purely as a means of preventing iris prolapse. In 1989 MacFarland recognized the advantages of implantation of foldable lenses with the self-sealing incisions, but it was Ernst in 1990 who recognized that this long scleral entry, with a tunnel configuration, coupled with a corneal shelf acted as a one-way valve and

thus explained the mechanism for self-apposition and changed the name from corneal shelf to posterior corneal lip.

Howard Fine in 1992 presented his self-sealing temporal corneal tunnel incision at the annual meeting of the American Society of Cataract and Refractive Surgery (ASCRS) and from that time onwards it has become an extremely popular technique.

Giving appropriate credit to many surgeons all over the world who had favored corneal incisions for cataract surgery, the leaders in this field were Harms and

Mackinson in Germany in 1967, Charles Elm in 1968, Troutman in 1973. In Japan, one of the leading proponents was Kimiya Shimuju.

In a recent survey in Eye World magazine, 60 percent of the American surgeons surveyed utilize self-sealing clear corneal cataract incisions for phacoemulsification and foldable IOL implantation. It is anticipated the number will perhaps double by the next year.

CONTROVERSIES REGARDING CLEAR CORNEAL INCISIONS

The indications for clear corneal cataract surgery have expanded significantly since the last few years. Initially the indications were limited to those patients on anticoagulants, with blood dyscrasias, patients with cicatrizing diseases such as ocular pemphigoid, or Stevens Johnson syndrome. However, the greatest advantage of the clear corneal incision has been the ability to do surgery with topical anesthesia. With the ability to avoid an injection into the orbit, with all its attendant risks, or utilization of intravenous medication in patients with cardiovascular insufficiency, or enhanced risk in patients with general debility, clear corneal cataract surgery became automatically the ideal technique.

Another big advantage of clear corneal incisions was that the clear corneal incision technique is topographically astigmatism neutral. With inherent astigmatic neutrality, the predictability of additional astigmatic and cylindrical reducing techniques like arcuate or limbal keratotomy became more predictably effective. The advent of phakic IOL as well as multifocal IOLs has led to stress to gain accuracy not only with the basic power, but to avoid any further development of astigmatism and reduce significantly, if not eliminate astigmatism.

Advantages of the temporal clear corneal incision include better preservation of pre-existing corneal configuration, with better preservation of the limbal zone at the 12 O’clock position for future filtering surgery. In cases with tight lids where the exposure is poor, the temporal incision makes life much easier for the surgeon. In addition, drainage from the temporal site is easier as the fluid trickles out from the naturally draining side zone.

A fair quantum of controversy regarding the clear corneal incisions was the major concern of increased incidence of endophthalmitis secondary to delayed chamber reformation. It was felt that poor wound healing enhanced the possibility of late postoperative infection. Fortunately, a significant number of very meticulous studies have shown that with a well-designed trapdoor incision, a clear corneal incision, be it placed vertically or temporally does not leak, and thus does not in any way

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enhance the risks. On the other hand, the relative simplicity, the superb clarity the next day and the quiet eye far outweigh any inconvenience involved.

CLASSIFICATION OF CORNEAL TUNNEL INCISIONS (after Fine et al) Location

•Corneal tunnel incision—entry posterior to limbus, exit at the cornea-scleral junction

•Corneal tunnel incision—entry just posterior to limbus, exit in clear cornea.

•Clear corneal tunnel incision—entry and exit in the clear cornea.

Architecture

•Single plane no groove

•Shallow groove < 400 microns

•Deep groove > 400 microns

Size and Planar Configuration

•Single-plane incision 2.5 by 1.5 mm rectangular tunnel

•Two-plane incision 2.5 by 1.5 mm rectangular tunnel

•Three-plane incision 2.5 by 1.5 mm rectangular tunnel plus a perpendicular arcuate component.

STRENGTH OF CLEAR CORNEAL INCISIONS VERSUS LIMBAL OR SCLERAL INCISIONS

Paul Ernst in 1994, demonstrated that rectangular clear corneal incisions in animal models show higher resistance to external deformation utilizing pinpoint pressure as compared to square limbal incisions.

The question of stability of the corneal tunnel has been the challenge of pinpoint pressure. The concept has been that whether cataract wound strength should be evaluated by challenging one’s incision using a pinpoint pressure on the posterior lip of the incision. Howard Fine and many other surgeons have demonstrated that it is not a correct test, as it is very unlikely that the patient would challenge his or her own wound strength by pressing with so fine an instrument as to pinpoint the exact site of pressure, which may leak. It is more appropriate to check the challenge with a blunt hook, which closely resembles the pressure, induced by a fingertip or knuckle, which is the most likely way the patient, would exert pressure. It is very unlikely that even a small percentage of incisions would leak spontaneously with blunt pressure (Fig. 9.1).

Questions have been raised regarding the relative safety of clear corneal incision versus a limbal-based corneal incision. Though, in theory, the limbal-based corneal incision would heal faster, and have a stronger ability to prevent leakage, the corneal incision gives excellent stability against leakage, and against accidental pressure.The one big disadvantage of the limbal-based corneal incision is the greater likelihood of ballooning of the conjunctiva, either at the site of the incision or even sometimes

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the complete conjunctiva, billowing forwards, making visualization of the anterior chamber structures during the surgical procedure more difficult.

A point of caution Park in 1997 has demonstrated that violation of the glaucoma bleb could threaten the integrity, not only of pre-existing filtering bleb but could also make the zone very amenable to subsequent infection. In addition, there is always likelihood that even a minor trauma like a hard rub to the eye could lead to a small hemorrhage.

TECHNIQUES

Fine et al in 1992 described the first self-sealing corneal tunnel incision for small incision cataract surgery utilizing a 3.00 mm diamond knife. The technique utilized was a two-plane incision. The first incision was performed perpendicular to the plane of the cornea (Fig. 9.2). The depth of the incision is kept at roughly 200 microns. Though ideally done with a calibrated diamond knife, it is more often, than not, done using the unguarded edge of the diamond knife, with the incision being made a little deeper than a superficial scratch. In doing the second plane, the knife enters deep into the primary incision and then continues in a plane parallel to the corneal plane, forming the cleavage in the corneal stroma. In practice it is simple to do, if the operating surgeon places the flat of the diamond blade, opposed to the conjunctiva, and then enters via the primary incision made. It gives a virtually perfect placement in the stromal zone (Fig. 9.3). The tip of the diamond knife after a 2 mm tunnel is constructed, is then allowed to “dimple” the edge of the Descemet’s, and is then simply pushed forward in the same plane, to achieve a cut in a straightline configuration (Fig. 9.4).

Alternatively, the surgeon can use a round disk knife to dissect open a shallow stromal tunnel of the required length and then enter the chamber with the knife. Caution should be used in not entering the chamber with the rounded disk knife as it does not give a straight line cut and will compromise the valve function of the incision.

90 THE ART OF PHACOEMULSIFICATION

Paul Ernst has clearly demonstrated that to be astigmatically neutral the incision should be squared. (i.e. the length and the width of the tunnel should be equal).

Williamson in 1993 was the first to utilize a 300 to 400 microns primary clear corneal incision. Rationale for the Williamson incision was that a thicker external edge to the roof of the tunnel had a less likelihood of tearing.

Langerman in 1994 described the single hinge incision in which the primary incision was made vertically in the cornea for a depth of ¾ of the cornea (400 microns) with the calibrated diamond knife. Subsequently, half way through the depth of the incision a horizontal groove is made in the stroma. The knife is then passed parallel to the corneal plane for a length of 2.00 mm, is dipped down to dimple the Descemet’s membrane and penetrates into the anterior chamber. Langerman felt that this initial “hinge” gave total protection towards accidental leakage of aqueous by pressure on the posterior flange of the incision. This technique led to an improved resistance for leakage from the incisional edges by the application of external pressure leading to deformation.

New Blade Technologies

The Fine Tri-diamond knife was developed with Mastel so that the entry incision into the cornea and exit from the cornea into the anterior chamber could be made in an extremely sharp thin line without a necessity to depress the tip of the knife down which often results in a tendency for tearing of tissue or scrolling of the Descemet’s membrane. It also makes for a superb self-sealing valve.

Rhein Medical developed a 3-D blade of 2.8 mm in width. This blade has differential slopes on the anterior and posterior surfaces, so that the forces of the tissues exerted along the blade will automatically allow the blade to “flow” in the plane of the cornea with no risk of an early entry nor of an inadvertent anterior escape. One simply places the tip of the blade where one desires the external incision. The blade is then pushed in the plane of the cornea with no attempt to applanate the cornea or attempt to enter the eye by dimpling. Perfect incision can be made rapidly, and more importantly, reproducibly produced.

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CLEAR CORNEAL INCISIONS AND ASTIGMATISM

One has to clearly understand the rationale of clear corneal incisions

•Excellent access to the anterior chamber for proper rhexis performance and access to the cataract and for IOL placement.

•Virtually bloodless incision

•Enables the formation of a self-sealing incision, resistant to deformation or leakage.

•Variable incision architecture to reduce or eliminate pre-existing astigmatism

•Faster physical rehabilitation of the patient. Most surgeons will permit immediate postoperative bending over by the patients or even strenuous physical activity without the risk of wound disruption.

•Being an anastigmatic incision, the refractive stability is almost perfect enabling additional reading spectacles to be prescribed in 4 days time.

•A much quieter eye, with faster healing, virtually no irritation or redness and no “flag” signs of inflammation.

TOPOGRAPHIC CONTROL OF CORNEAL ASTIGMATISM

Astigmatism has always been an integral part of cataract surgery. Intracapsular cataract extraction (ICCE) is still popular in many parts of the world especially in Asia, Middle East and Africa. The ICCE technique generally utilized the Graefe knife or scissor based, 180-degree corneal incision. Subsequent wound closure by suturing with 10/0 nylon usually saddled the poor patient with an exorbitant quantum of variable astigmatism. The shift to extracapsular cataract surgery (ECCE) did little to reduce the astigmatism, as invariably a two plane or a three plane, large implant had to be inserted.

It was the advent of phacoemulsification that has made the surgeon, and the patient, appreciate the advantages of small incision surgery and apply the concept in an endeavor to reduce astigmatism still further. The greatest advantage of clear corneal < 3.00 mm (also termed sub-three) incision, was that it was literally an astigmatic neutral incision. Evaluating corneal changes utilizing the computerized corneal topographer has significantly improved the understanding of how these incisions work and what has to be done to reduce their astigmatic tendencies.

Ideally, corneal topography should be done in all cases in an effort to evaluate the astigmatic component and the resting status of the cornea. In order to understand the effect of clear corneal sutureless incisions, one has to comprehend that the shape of the corneal dome is derived partly from lamellar collagen bundles and the relative elasticity of the corneal tissue. Trauma induced to a cornea, be it an injury or even simply, surgery, affects the regularity of the corneal surface. As the lesions heal, alterations are induced to the corneal shape.

It must however be clearly appreciated that while a corneal incision made of 2.8 mm size will induce no topographically demonstratable astigmatic changes whatsoever, one of 4.00 mm or 5.00 mm will induce against-the-rule (ART) astigmatism, more so, if the incisions are not properly constructed.