Ординатура / Офтальмология / Английские материалы / The Art and the Science of Cataract Surgery_Boyd, Barraquer_2000

In previous chapters we have discussed

in depth how to evaluate the patient preoperatively (Chapter 2), how to calculate the correct IOL power in standard and complex cases (Chapter 3), prevent major complications such as infection (Chapter 4), and how to proceed with the operation by using adequate, modern anesthesia and to make the operating room efficient (Chapter 5). Why phacoemulsification is so important (Chapter 6), how to make the transition from ECCE to phacoemulsification with minimum risk to the patient while minimizing mental and emotional trauma to the surgeon (Chapter 7), what are the best instruments and equipments to use in phacoemulsification (Chapter 8), are all essential experiences and information for the modern cataract surgeon. In addition, you may also find the state of the art phacoemulsification techniques and facilitate your understanding of each group of procedures so that you can establish a basis for your own selection of the procedure that will lead you to master phacoemulsification (Chapters 9 and 10). Finally, a discussion of the most important complications you may encounter in phacoemulsification and in planned extracapsulars and how to manage them successfully is presented in Chapter 11.

Aims of this Chapter

Based on the tools and concepts provided in Chapters 1-11, in this Chapter we carefully consider, in depth, powerful techniques available today which allow the use of phacoemulsification in the management of complex, and more challenging cases.

Broadening of Indications

As emphasized by Miguel Angelo Padilha, M.D., F.B.C.S., one of Brazil’s most prestigious anterior segment surgeons, the progressive mastering of phacoemulsification (Chapter 9) by an increasing number of surgeons in various parts of the world allows indications for this procedure to broaden rapidly extending to the complex cases that were previously considered a contraindication to phaco. Patients with very hard cataracts, classified as “rock hard cataracts”, eyes with shallow anterior chamber, pseudoexfoliation, subluxated cataracts, cornea guttata, corneal dystrophies, corneal transparency alterations, as well as small pupils, were previously considered contraindications to the use of this technique.

In this chapter, we intend to provide the cataract surgeon with practical clinical observations, strategies and surgical techniques leading to safe and efficient management of cataract surgery in special situations that we refer to as «the Complex Cases.» Although much of the focus is on phacoemulsification, many of the approaches to complex cases here presented are also applicable to manual extracapsular.

Complex Cases Already Discussed in

Previous Chapters

They are: 1) Cataract surgery in patients with diabetic retinopathy (pages 21-27, Figs. 8-18). 2) In age-related macular degeneration (pages 28-29, Figs. 19-20). 3) In the presence of retinal breaks (pages 28-30, Fig. 21). 4) In uveitis (pages 31,33, Fig. 22). 5) In adult strabismus with partial amblyopia (page 33). 6) Determining IOL power in complex cases (pages 48-58, Figs. 24-32).

viscoelastics years ago as his «third assistant.» Viscoelastics are very important for cataract surgery, whether in routine or complex cases. Their main uses are for maintaining the anterior chamber depth, protecting the endothelium, as aids during capsulorhexis, hydrodissection, phacoemulsification, with I/A, maintaining the capsular bag fully open a intraocular lens during insertion, unfolding, and positioning of the IOL.

They have a special place in this chapter because their adequate use has become even more valuable and indispensable in the management of complex cases.

Cohesive and Dispersive

Viscoelastics

In the past few years, industry has refined viscoelastics, and made their properties more specific so that we now have available two main groups, each type better than the other for specific functions. As clarified by Buratto, these groups are: 1) cohesive,

2) dispersive.

FOCUSING ON THE MAIN COMPLEX CASES

THE DIFFERENT TYPES OF VISCOELASTICS

Their Specific Roles

For years we have generally referred to viscoelastics (VES) as highly valuable protective and space-maintaining substances.

Joaquin Barraquer, M.D., referred to

The Cohesive VES -

Specific Properties

The better known cohesives are those with high viscosity, such as Healon GV, Healon, Provisc, Amvisc Plus, Amvisc, and Biolon. They are very useful in creating space and stabilizing the tissues, increasing mydriasis, supporting the nucleus during capsulorhexis, deepening the anterior chamber, separating synechiae, opening the capsular bag and maintaining this space during implantation of the IOL.

The cohesive viscoelastics maintain space really well because the molecules hold themselves together. They are also quite easy

to remove. If you are trying to create a space such as when opening the capsular bag, or deepening the anterior chamber, then the cohesive viscoelastics are going to work better.

The Dispersive VES-

Specific Properties

The dispersive VES are those with lower viscosity and lower cohesiveness. They break up easily when injected into the eye and therefore disperse in small fragments. This group includes Viscoat (Alcon), Vitrax (Allergan) and the methylcellulose products. These substances form a layer that will adhere and coat the posterior surface of the cornea to protect the endothelium during phacoemulsification, or from other instrumentation during manual ECCE. They help in capturing nuclear fragments. They are also valuable if the phacoemulsification tip accidentally catches the iris, in zonular disinsertion and rupture of the posterior capsule.

The dispersive viscoelastics are excellent coaters. If you aim to reduce the friction between the intraocular lens optic and the injector, so you are less likely to tear the intraocular lens, Lindstrom uses a dispersive viscoelastic. Or, if you are operating on an eye with a dry or somewhat opaque surface, placing a few drops of the dispersive viscoelastic on the surface clears the view significantly. If you tear the posterior capsule, but have not lost vitreous yet, if you again inject a dispersive viscoelastic, it can stay in the eye over the tear and the capsule, to hold vitreous back and protect the capsule while you carefully remove the nuclear remnants or a little cortex. That can be very helpful.

But the dispersives are a little more difficult to remove and they do not maintain space as well. Consequently, the choice of VES varies with the surgical requirements of

each particular case. Each surgeon must be sufficiently trained to choose the most appropriate substance for the individual patient and the specific technique.

PHACOEMULSIFICATION AFTER PREVIOUS REFRACTIVE SURGERY

The primary challenge in operating on patients who have already had radial keratotomy (RK) or excimer laser surgery is selection of the appropriate lens power. As the corneal curvature is altered, the usual predictive formulas have also been altered. Standard ultrasound A-scan technology and corneal curvature are still used to estimate the appropriate lens implant for reaching the target refraction. In addition, if the fellow eye has not had refractive surgery, that eye is also measured.

We have already discussed this subject in practical and specific terms for the clinician in pages 50-54 and presented the methods and formulas most often used. Since there is no universally accepted formula to calculate these patient’s IOL power accurately, we present here the method used by a master cataract surgeon to solve this problem.

Jack Dodick, M.D., has found the following procedure quite effective. He implants a specifically designated lens under topical anesthesia with sutureless clear corneal wound. Following the operation, the patient is taken to an autorefractor just minutes after surgery. If there is a high ametropia present, the patient returns to the table, the eye is again prepped, the lens is removed and replaced with one of the appropriate power. In patients with high myopia, for example, the surgeon’s best judgment about lens implant power can be considerably off target because

of untoward circumstances like a staphyloma. In patients who have had RK, surgeons tend to underestimate the power of the lens implant.

Removing the lens does not present a major problem. The challenge is to remove the lens without enlarging the small incision and implant another through the same small incision . If the original 6 mm or 5.5 mm optic has been implanted through a 3.2 mm incision by folding; it is important to remove the lens without sacrificing the length of the wound. This is done quite simply by bisecting the optic with Gills’ capsulotomy scissors under viscoelastic and removing the hinged two halves through the small incision. This technique for removing the foldable lens is presented in Figs. 165 and 166, Chapter 11.

PHACOEMULSIFICATION IN HIGH MYOPIA

In patients with high myopia, phacoemulsification is somewhat more challenging than in other eyes. Patients with high myopia have globes that are superelongated and sclera that is thinned out. The minute the phaco probe is inserted and the infusion starts, the chamber deepens dramatically (Fig. 169). The probe must reach deep into the eye to access the nucleus because the lens iris diaphragm may have moved considerably back. Dodick has sought to overcome this problem by lowering the bottle height and reducing the flow, so that the lens is unlikely to move to such a posterior location. Even when this occurs, it is still quite possible with

high vacuum to bring the nucleus up into the pupillary plane earlier than with a normal or emmetropic eye. Phaco chop helps further by cutting the nucleus in several pieces and bringing these pieces up into the pupillary plane with high vacuum.

The challenges in calculating the correct IOL power in high myopia are discussed on page 50.

CHALLENGES OF PHACOEMULSIFICATION IN HYPEROPIA

The challenge in hyperopia is somewhat different. Dodick refers to these as crowded eyes because all of the small anatomical structures are in a smaller, confined space. Positive pressure is more likely to occur. Dodick makes two fundamental adjustments in technique when dealing with an extremely hyperopic eye. First, he dehydrates the vitreous with an osmotic agent such as Mannitol. Secondly, he tries to compress the eye and to express some of the unbound water in the vitreous with a compressive device like an Honan balloon (Fig. 96). He leaves this Honan balloon on at about 35 to 40 mm Hg for 20 to 30 minutes. These two preparatory steps help reduce the volume of the eye and soften the eye prior to nucleus removal.

The challenges in calculating the correct IOL power in high hyperopia are presented on page 48. The pros and cons of piggyback lenses in very high hyperopia are discussed on page 49.

REFRACTIVE CATARACT SURGERY

Why and When Do Refractive

Cataract Surgery

Richard Lindstrom, M.D. has become an advocate of what he calls «refractive cataract surgery», by which we mean trying to improve the patient’s astigmatism at the time of cataract surgery.

In his extensive research and clinical experience, about 70% of the cataract patients that he operates have less than one diopter of astigmatism preoperatively and about 30% have more than one. He does not make any astigmatic corrections in those that have less than one diopter. That is good enough for 20/30 uncorrected visual acuity. Lindstrom becomes somewhat more aggressive with astigmatism when there are two diopters or more before the cataract operation. His goal is to reduce it to one diopter; not to try to correct it all, just to get it down into a reasonable range. He advises making the combined operation for cataract and astigmatism only when performing phacoemulsification.

As a matter of fact, he advises against it if the phacoemulsification incision, is enlarged to place a 6.5 or 7 millimeter optic PMMA IOL or when a planned ECCE is performed. In such cases, he recommends, doing the cataract surgery, see what you get, and then fix it later if there is a problem. Most patients adapt to glasses. This is be-

cause with an incision of this size, it is almost impossible to plan the refractive operation. The range of effect on astigmatism with such incisions is significant. With a planned extracapsular wound one patient might change a diopter and another might change four diopters.

TECHNIQUE FOR REFRACTIVE CATARACT SURGERY

Surgical Principles

Lindstrom’s surgical principles and technique are as follows:

1)Move the cataract 3 mm tunnel incision to the steeper meridian (Fig. 170). He thinks of this small wound as an astigmatic keratotomy. This will reduce the present astigmatism by 0.50 diopters. If the patient has 1 diopter of plus cylinder at axis 90, and a 3 mm cataract incision is made at axis 90, he/she will end up with only a 1/2 diopter of cylinder. If they have +1 diopter at 180 and the 3 mm cataract/IOL incision is moved over to the temporal side where the steeper meridian is located, they will end up with only +1/2 diopter of astigmatism at 180º which is good enough for 20/20 vision uncorrected. Lindstrom’s approach is to make them better, not to correct all the astigmatism. If they have 1.5 diopters, they will end up with 1 diopter cylinder and that is acceptable. But if they have 2 diopters to begin with, they will end up with 1.5 diopters and that is outside his goal. Lindstrom’s outcome goal is 1 diopter astigmatism or less.

2)If more than 1.0 diopter of astigmatism would remain, Lindstrom applies the

principles of astigmatic keratotomy at the time of surgery. He does this very conservatively. The cataract wound becomes one astigmatic keratotomy. On the opposite side, at a 7 mm optical zone, he will make a small 2 mm corneal incision to correct 1 diopter or a 3 mm long incision to correct 2 diopters of astigmatism in the cataract age group. This becomes a second astigmatic keratotomy (Fig. 170).

If the patient preoperatively has 3 diopters of astigmatism, Lindstrom places the 3 mm cataract/IOL incision again on the steeper meridian. This brings the astigmatism down to 2-1/2. If he wants the patient to end up with 1/2 diopters instead of 2 1/2 diopters of astigmatism, he makes a small 3 mm, nonperforating corneal incision with a diamond knife on the opposite side of the cataract incision at a 7 mm optical zone (Fig. 170).

Surgical Procedure

Lindstrom sets the depth of the diamond blade at 600 microns. In that area on the average the cornea is about 650 microns thick so it is a very safe setting so as not to perforate the cornea. This incision can be done at the very beginning of the surgery. The first thing to do is make this little tiny cut. The other alternative is to complete the cataract operation, firm up the eye, and make that tiny cut at the end, but that may be more difficult.

The exact location of this cut in the cornea is 3.5 mm from the center of the cornea. By using a 7 mm optical zone, the cut is really 3.5 mm from the center of the cornea. The diameter of the cornea is 12 mm. The limbus is 6 mm from the center.

C h a p t e r 12: Cataract Surger y in Complex Cases

Figure 170 (above)): Technique for Refractive Cataract Surgery

Dr. Lindstrom places the 3 mm cataract tunnel incision (C) in the steeper meridian to reduce pre-op astigmatism when present in a cataract patient. Further reduction of astigmatism may be obtained with a corneal incision (A) placed opposite the cataract incision in the same axis at the 7 mm optical zone (dotted line). The example shows a patient with pre-op 3 diopters of plus cylinder at axis 145º (inset). The corneal cataract incision is placed in this axis and may reduce the pre-op astigmatism by 0.50 diopters. The 3 mm straight corneal incision placed opposite the cataract incision in the same axis at the 7 mm optical zone should reduce astigmatism further by 2.0 diopters. The two together will reduce astigmatism a total of 2.5 diopters.

Why Straight Cuts Instead of

Arcuate

Lindstrom uses a 7 mm optical zone marker that has little marks on it for 30, 45, 60 and 90 degrees. At a 7 mm zone a 30 degree arcuate cut is equivalent to a 2 mm straight cut and a 45 degree arcuate cut is equivalent to a 3 mm straight cut (Fig. 171). Lindstrom finds that it is safer and easier

Figure 171 (below): Length of Straight Corneal Incision Related to Arcuate Incision

At the 7 mm optical zone (dotted line), a 30º

Dr. Lindstrom finds that it is safer and easier to make such small incisions straight rather than arcuate.

just to make these small incisions straight instead of arcuate. With this technique he tries to make things safe and better for the patient, not perfect, and without doing any harm. This means trying to bring a patient from 3.5 diopters of astigmatism down to one, in order to improve the quality of his/her vision. He finds that he can enhance the results to the point now where about 85% to 90% of the patients will have 1 diopter or less of astigmatism.

Lindstrom finds that these tiny incisions programmed as outlined here are a very powerful tool and seem to be very safe. He

has not observed any major complications such as poor wound healing, infection or perforation.

Full Refractive Correction of

the Cataract Patient

By selecting the correct IOL power even in complex cases as outlined in pages 45-54, correcting the preexisting astigmatism as discussed here and further enhancement with the use of toric foldable IOL’s if necessary (see Chapter 9), we have the means to create in our patients the truly refractive cataract operation.

Age related cataract and primary open-angle glaucoma or chronic angle closure glaucoma often coexist in the older population. With increasing longevity this is becoming more prevalent. The management of such cases has been controversial because medical or surgical therapy of one condition often affects the other.

Most of the concepts and techniques presented in this chapter are based on the experiences and observations of Maurice H. Luntz, M.D., Chief of the Glaucoma Service at the Manhattan Eye and Ear Hospital in New York.

Overview - Alternative

Approaches

When cataract and glaucoma coexist but the glaucoma is uncontrolled or poorly controlled, one approach is to give priority to control of the glaucoma either with additional medication or if this is not possible,

with laser trabeculoplasty or filtration surgery. Luntz believes that this approach has its drawbacks. Medical therapy for glaucoma may necessitate miotics, which tend to reduce visual acuity regardless of preexisting lens opacities, and may encourage an acceleration of cataract progression. Surgical therapy of glaucoma may be associated with increased lens opacification, especially if the surgery is complicated by inadvertent lens trauma but even in the absence of lens trauma. Subsequent cataract extraction, even if a functioning bleb and good drainage are obtained, results in loss of the bleb in approximately 10% of eyes, and inability to restore control of the glaucoma.

When the indications for cataract extraction are present but the glaucoma is controlled medically, the most common approach has been to remove the cataract and continue medical management of the glaucoma. Intraocular pressure is more easily controlled in some eyes after lens extraction but a significant number of these patients will require

glaucoma surgery as early as 3-6 months after standard cataract extraction . The patient then faces a second surgical procedure with its attendant risks soon after the first operation.

An alternative approach is combined cataract and glaucoma surgery. Most surgeons are now oriented toward this approach. Excellent results are reported with extracapsular cataract extraction and trabeculectomy (Luntz and Stein, 1988; Simmons, 1992) and phacoemulsification with trabeculectomy. The combined procedure is used in those patients in whom IOP runs above the upper limit of the target IOP for that patient, or in whom good control of IOP necessitates the use of three or more different drugs. In those patients in whom IOP is well controlled using no more than two different drugs, phacoemulsification alone will generally maintain adequate postoperative control.

COMBINED CATARACT SURGERY AND TRABECULECTOMY

In this chapter, we will first present the evolution of the different types of Combined Procedures for Cataract Extraction and Trabeculectomy as described by Luntz, to provide you with an instant mental picture of the different approaches to this problem, the latest being combining phacoemulsification with a tunnel incision and trabeculectomy. Considering that this Volume covers all major, widely accepted cataract surgery procedures, we present the advanced techniques in combined surgery for glaucoma with phacoemulsification as well as with planned extracapsular. The evolution of the different types of combined cataract extraction-trab- eculectomy is presented in Figs. 172, 173,

174, 175, the combined extracapsular extraction with trabeculectomy step by step in Figs. 176 through 181, and phacoemulsification combined with trabeculectomy step by step in Figs. 182 through 187.

Indications

The indications based on Luntz’s observations are: 1) Any eye with open angle glaucoma and cataract in which surgery is required for the cataract, even if the glaucoma can be medically controlled but requires more than two medications to do so. If combined surgery is not done, many of these eyes will require glaucoma surgery at a later date, exposing the patient to two surgical procedures where one would have sufficed. An exception to this are those patients in whom IOP with three medications runs in the very low teens (10-11mm Hg).

2) Eyes with uncontrolled glaucoma requiring glaucoma surgery and significant cataract with corrected vision of 20/40 or less, reading 6-pt. print or less or with poor glare tolerance.

Evolution of the Incision for Combined Cataract Extraction and Trabeculectomy

The combined operation for cataract and glaucoma constitutes two procedures performed at the same surgical session. The technique for each procedure remains unchanged but the surgical incision needs to be modified using either separate incisions for each procedure (Fig. 172) or combining the incisions for each operation into one compound incision (Figs. 173, 174, 175).