18

Incisions

Luis W Lu, Alejandro Espaillat

Ana Claudia Arenas

Francisco Contreras-Campos

Introduction

Intracapsular cataract extraction, popular during the 1970s, generally utilized a large corneal incision performed superiorly creating an against-the-rule astigmatism as a consequence. The switch to extracapsular cataract extraction (ECCE) with intraocular lens (IOL) implantation was a real improvement in the quality of vision, but did little to resolve the post cataract astigmatic errors due to the large incisions needed to introduce the IOL. With the introduction of phacoemulsification, and new foldable IOL designs, creating the correct small incision became crucial to determine the successful outcome of the procedure, and minimize the residual amount of astigmatism.

The Limbal Incision

In 1989, McFarland and Ernest introduced an incision architecture that allowed the phacoemulsification, and intraocular lens implantation without the need of suturing. Besides lengthening the “scleral tunnel”, as named by Girard and Hoffmann, this incision ended in a corneal entrance and a posterior lip, the so-called corneal lip, which acted as a one-way valve with 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 self-sealability as well as but also astigmatism neutrality.

There are two aspect views of these incisions: sagittal and anteroposterior; and three components: the external incision, the intratissue tunnel and the internal incision. From the sagittal aspect, limbal incisions can be made in one of the following configurations varying between single-plane, grooved beveled and, triplane with a groove and a bevel.

The external component may also be in one of the following theoretical configurations: the singlestep “stab” incision, as initially introduced by Howard Fine, and the two-step grooved incision by Charles Williamson, who felt that the wound should be larger on the outside than the inside, creating a trapezoid configuration.

The sagittal shape, and the direction of the tunnel may also vary, but usually are made flat by blades advancing in a single plane. On the other hand, its anteroposterior configuration can be as a parallelogram.

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The third component of these incisions, the internal opening, may have a single-plane “Stab” or biplane “Steeped” sagittal shape. The anteroposterior aspect of the wound incision could be made limbus-parallel, tangential, or limbus antiparallel “corneal frown”.

The limbal incision could be located superior, oblique or temporal. Superiorly located incisions, when not under the influence of sutures, are known to have an against-the-rule astigmatic effect. The oblique location, whether nasal or temporal, is advocated by some surgeons who prefer this site for ergonomic reasons as well as for greater wound stability. The temporal wound incision has been shown to be the most astigmatically neutral of

these three locations, achieving stability almost immediately, and maintaining it for life.1,2

The limbal incision is very simple to perform making the maneuvers of entrance, and instrumental manipulation easy for the surgeon. It is used primarily by the surgeon in transition to phacoemulsification from the classic ECCE. The technique usually starts with a conjunctival peritomy, followed by a perpendicular limbal incision made with a metal or diamond blade, and an oblique entrance to the anterior chamber (Fig. 18.1). The length of the incision could be as small as 2.5 mm initially to keep a close system, and a deep anterior chamber during the phacoemulsif ication procedure, then it could be enlarged up to 6.0 mm, depending on the type of the IOL used.

FIGURE 18.1 Limbal incision. Oblique entrance to the anterior chamber

Both limbal and clear corneal incisions heal by fibroblast response. The key is the timing of the healing process: 7 days for vascular origin (limbal) and 60 days for a vascular origin (corneal). Clear corneal incisions are also more subject to foreign body sensation than limbal incisions.1,2

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scleral incision with calipers, followed by the creation of a vertical groove of a desired length and configuration, 40 to 50 percent scleral depth, using a microsurgical steel or diamond blade held perpendicular to the surface of the sclera. The second step is the creation of the scleral tunnel, with a rounded crescent blade, dissecting a lamellar flap anteriorly through the sclera, 1 to 2 mm into clear cornea. The dissection is carried forward to Descemet’s membrane at the anterior edge of the vascular arcade. The last step is the advancement of the scleral tunnel incision, aiming the tip of the keratome toward the center of the lens, dimpling the Descemet’s membrane of the cornea, before entering the anterior chamber creating a triplanar self-sealing incision.

The scleral tunnel must extend into the clear cornea to avoid the prolapse of the iris, damage to the structures of the chamber angle, fluid loss and a flat anterior chamber, and to create a valve effect which will seal the wound at the end of the surgery. Some of the disadvantages of the scleral tunnel incisions are that it can surgically induce astigmatism, from the use of cautery to control bleeding conjunctival, and episcleral vessels,5,6 presents a difficult access to the anterior chamber with limited movement of the surgical instruments, and a difficult access to the lens nucleus, aspiration of the lens cortex, and IOL manipulation.

The Clear Corneal Incisions

The more advanced incision for phacoemulsification surgery is the clear-cornea incision. 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. Another big advantage of clear corneal incisions is the tremendous safety with relative astigmatism neutrality, coupled with exceptional results.

This is a bloodless, self-sealing, sutureless, and quick incision, best performed temporally, where the distance from the visual axis to the periphery is longer, and accessibility to the eye is optimal. This temporal approach includes also better preservation of pre-existing corneal configuration, and of the limbal zone at the 12 o’clock position in case of a future filtering surgery. It can also be used to reduce the patient’s natural astigmatism by approximately 0.50 diopters in that meridian.5,6

This type of incisions can be classified, after Fine, depending on:

I-Location

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

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

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

II-Architecture

• Single plane no groove

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•Shallow groove<400 microns

•Deep groove>400 microns

III-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 perpendicular arcuate component.

When making the incision, a decision must be made as whether to groove or not to groove, the external aspect to the incision. Non-grooved single-plane incisions utilize a 2.5 to 3.0 mm steel or diamond knife.7 First the anterior chamber is filled with a viscoelastic agent through the paracentesis site, giving the eye stability prior to entry into the anterior chamber. The globe is then fixated with a fixation ring or forceps to avoid creating conjunctival tears, hemorrhages, or corneal abrasions. The uniplanar incision is made inserting the blade in-and-out through the cornea at the surgical limbus, 1 mm anterior to the limbal vessels in the plane of the cornea until the shoulders, which are 2 mm posterior to the point of the knife, touch the external edge of the incision. After the tip enters the anterior chamber, the initial plane of the knife is re-established to cut through Descemet’s in a straight line configuration.

A grooved, triplanar, self sealing, clear-cornea incision has three steps. The first step is the creation of an approximately 300 µm deep, perpendicular incision to the corneal surface, 1 mm anterior to the limbal vessels, using steel or preferably a calibrated diamond blade. The second step is the creation of a 1.75 to 2 mm stromal tunnel, parallel to the iris plane, dissecting the corneal stroma in a lamellar fashion.

The third and final step is to downward tilt the keratome blade 30 degrees toward the visual axis, in order to penetrate the anterior chamber.8 The stability of the wound depends on the construction of the internal valve, the total width of the incision, and the length of the tunnel.9 Generally, the clearcorneal incision is limited to 4 or 5 mm in length in order to be self-sealing. The use of a foldable IOL that could be inserted through a 3 to 4 mm incision allows the surgeon to perform a purely corneal sutureless tunnel of 1.5 to 2.0 mm length, with minimal variation in the preexisting astigmatism.10

When properly created, the clear-cornea incision will seal by itself. This can be hastened by stromal hydration.11 Stromal hydration is best accomplished by the injection of fluid via syringe attached to a 27-gauge cannula tightly against the lateral wall of the deeper layers of the incision causing immediate opacification. All properly created incisions usually seal after 1 to 2 minutes, when the stroma opposes properly.

In summary, one has to understand the rationale of clear corneal incisions:

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

•Virtually bloodless incision.

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

•Variable incision architecture capable of eliminating pre-existing astigmatism.

•Faster physical rehabilitation of the patient.

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•Being an anastigmatic incision, the refractive stability is almost perfect, enabling additional reading spectacles to be prescribed in a short period of time.

•Faster healing with virtually no irritation, and redness.

The Side Port Incision

A side port incision is a small paracentesis limbal incision 1 mm wide, and 0.75 mm long, usually created 90 degrees away from the main incision, using a 15–30 degrees metal blade, or a 1 mm diamond blade.

The side port incision should always be used during phacoemulsification because it provides an access route for the introduction of viscoelastic, saline, anesthetics, and antibiotics to the anterior chamber. It can also be used to introduce additional instruments during the surgery to stabilize the globe, manipulate the lens nucleus, protect the posterior capsule, keep the iris in place, and facilitate the removal of the lens cortex, as well as the insertion of the IOL.

The paracentesis incision is generally performed with the anterior chamber still closed, or with the chamber open but previously filled with a viscoelastic agent. The incision is performed through the clear cornea, just in front of the limbal vessels, tangential to the iris. The external end of the incision is usually larger than the internal wound, to facilitate the introduction of the surgical tools. When performed correctly the paracentesis incision is self-sealing. It is very important to avoid creating a paracentesis that is too narrow, wide, superficial, deep, anterior, or posterior, to facilitate the introduction of surgical instruments, and prevent fluid leakage, iris prolapse, and corneal folds.

Relaxing Incisions

Improved spherical and astigmatic outcomes are now well-recognized benefits of modern small-incision cataract surgery. The combination of limbal or corneal relaxing incisions with cataract surgery is fundamental to the current definition of “Refractive Cataract Surgery”, which has come to represent a reality for cataract patients.

Over the past several years, great efforts have been made to study the astigmatic effects of various cataract incisions. By manipulating the size, location, and shape of the incisions, surgeons could tailor the astigmatic outcome according to the patient’s preexisting astigmatism. If a patient has enough pre-existing astigmatism to warrant reduction, modern astigmatic keratotomy may then be conservatively added to arrive at the desired cylindrical outcome. Arcuate astigmatic relaxing incisions (RIs) have proven to be extremely safe and reliable,12 and have been used since the early 1970s to reduce high pre-existing astigmatism in cataract surgery.13 The RIs can be made at the limbus (LRIs), or at the cornea (CRIs), depending on the amount of astigmatism. Although CRIs remain a powerful tool for correcting high astigmatism, they have a limited predictability, and often may result in overcorrection particularly in patients with lower amounts of preoperative astigmatism. Most surgeons prefer to use LRIs to correct the pre-operative astigmatism, because they are easy to perform, more comfortable for the patient, result in more regular corneal topographies with less corneal distortion, postoperative refractions

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are less variable, overcorrections are rare, and are effective in patients with low to moderate astigmatism, usually 3 diopters or less.

To create a relaxing incision some surgeons advocate placing an orientation mark at the limbus at the 12 o’clock position before the patient is supine. The surgeon will then determine the amount, and axis of the corneal cylinder through corneal topography. The refractive cylinder is usually not considered in phakic patients, because any lenticular astigmatism would be removed by the cataract surgery, and cannot be included in the surgical plan. The LRIs are created using a diamond blade which incorporates an special preset 600-µm diamond microknife. The globe is fixated with a modified Fine-Thornton fixation ring, and the diamond blade is placed in the steep axis at the limbus just anterior to the palisades of Vogt, creating an incision of an appropriate length by visually following the degree marks on the metal ring. The number, and length of incisions are determined according to the various nomograms previously published.12–15 Astigmatic keratotomy, whether primary or associated with cataract surgery, is a simple, low-cost, and effective procedure. Following surgery, these incisions appear to heal quickly, and are nearly unidentifiable within several days leaving a long lasting effect on the patient’s quantity and quality of vision.

Cataract surgery is a procedure which is in a constant evolution, and undoubtedly will continue to improve in the future. In the mean time, following the previous suggestions will help surgeons achieve a successful outcome of a phacoemulsification cataract extraction.

References

1.Fine HI: Architecture and construction of a self-sealing incision for cataract surgery. J Cataract Refract Surg 17 (Supp):672–76, 1991.

2.Steinert RF, Brint SF, White SM, et al: Astigmatism after small incision cataract surgery: A prospective, randomized, multicenter comparison of 4 and 6.5 mm incisions. Ophthalmology 98:417–24, 1991.

3.Singer JA: Frown incision for minimizing induced astigmatism after small incision cataract surgery with rigid optic intraocular lens implantation. J Cataract Refractive Surgery 17(Supp): 677–88, 1991.

4.Koch PS: Mastering phacoemulsification: A simplified manual of strategies for the spring, crack and stop and chop technique. 4th ed. Thorofare, NJ: Slack, 19, 1994.

5.Long DA, Monica ML: A prospective evaluation of corneal curvature changes with 3.0 to 3.5 corneal tunnel phacoemulsification. Ophthalmology 103:226–32, 1996.

6.Ley land MD: Corneal curvature changes associated with corneal tunnel phacoemulsification. Ophthalmology 103: 867–88, 1996. Letter.

7.Fine IH: Self-sealing corneal tunnel incision for smallincision cataract surgery. Ocular Surgery News 1, 1992.

8.Williamson CH: Cataract keratotomy surgery. In: Fine IH, Fichman RA, Grabow HB, (Eds):

Clear-Corneal Cataract Surgery and Topical Anesthesia. Thorofare, NJ: SLACK; 87–93, 1993.

9.Buratto LL: Phacoemulsification: Principles and Techniques. 1st ed. Thorofare, NJ: Slack, 41, 1998.

10.Albert DM: Ophthalmic Surgery: Principles and Techniques. 1st ed. Maiden, MA: Blackwell Science, 25(283):1999.

11.Mackool RJ: Current Personal Phaco Procedure. In Fine IH (Ed): Clear-Corneal Lens Surgery. Thorofare, NJ: SLACK; 239–50, 1999.

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12.Gills JP, Gayton JL: Reducing pre-existing astigmatism. In Gills JP, Fenzl R, Martin RG, (Eds):

Cataract Surgery: The State-of-the Art. Thorofare, NJ: SLACK Inc; 1998.

13.Troutman RC: Management of pre-existing corneal astigmatism. In: Emery JM, Paton D, (Eds):

Current Concepts in Cataract Surgery. St. Louis, Mo: CV Mosby; 1976.

14.Masket S, Tennen DG: Astigmatic stabilization of 3.0 mm temporal clear corneal cataract incisions. J Cataract Refract Surg 22:1451–55, 1996.

15.Nichamin LD: Intraoperative astigmatism. In Ford JG, Karp CL, (Eds): Cataract Surgery and Intraocular Lenses, a 21st Century Perspective. Ophth. Monographs 7, 2nd ed. AAO, LEO series. 2001.