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

Nevertheless, he considers that there still are indications for the standard PMMA lenses, for example the secondary anterior chamber lens implant (Fig. 129). He also uses standard PMMA intraocular lenses when performing a triple procedure that includes a penetrating keratoplasty. In these patients there is no reason to use a foldable lens. He may use a 7 mm optic modified C loop PMMA lens.

MONOFOCAL FOLDABLE LENSES

An extensive variety of excellent monofocal foldable lenses are produced by manufacturers in the US, Germany, France, Belgium,Switzerlandandothercountries. They use the finest technology and front-line engineers, biochemists and designers.

Themostwidelyaccepted,majorgroups of foldable lenses are made of either acrylic or secondgeneration silicone (PDMDPS). Each grouphasadvantagesanddisadvantages. Other monofocal lenses creating interest are the Memory lens, the hydrogel lenses and the toric lens made by STAAR.

THE FOLDABLE ACRYLIC IOL'S

These lenses have a very high refractive index providing crystal clear vision. Chemically they are closely related to the still generally favored PMMA. Mechanically they are best described as pliable rather than elastic.

This is clinically important because acrylic lenses are comsidered by many surgeons as somewhat bulky when folded and, consequently, difficult to implant through an inci-

sion less than 3.5 mm. We have presented Carreño's technique in which he describes how to insert the AcrySof lens through a 2.8 mm incision in Chapter 8. The most widely used foldable acrylic lenses are the popular Alcon AcrySof lens model MA30BA, which has a 5.5 mm optic and PMMA haptics and the Allergan Sensar AR40 with a 6.0 mm optic. Theybothcomewithverypracticalfoldingand injector systems, the "Acrypack" for Alcon's AcrySof and the "Unfolder Saphire" for Allergan's Sensar.

Specific Advantages of Acrylic

Foldables

In addition to providing a very high refractive index, they are also the first choice lenses to use in higher risk cases such as patients with diabetic retinopathy (Figs. 8-17), chronic uveitis or any candidates for future vitrectomy with silicone oil.

Another advantage seems to be that acrylic lenses have a "tacky" surface. According to Tobias Neuhann, M.D., a positive consequence of this tackiness is a mechanicaladhesivenessbetweenlenscapsule and IOL, which, in turn, may lead to reduction of secondary cataract (posterior capsule opacification).

A disadvantage of this tackiness, however, is that a multitude of small particles may stick to the lens surface and be pressed into the material with the implantation instruments, where they remain forever, since they are not absorbed. Forthesereasons,injectorimplantation or disposable implantation forceps are gainingincreasingimportanceinhandlingthese lenses (Fig. 82 B and C).

Disadvantages of Acrylic

Foldables

Foldable acrylic lenses come in a 5.5 and a 6 mm optic size. Lindstrom and some other surgeons prefer the 6 mm optic because the 5.5 mm optic lenses may have problems with edge glare and unwanted visual images.

Another limitation with acrylic lenses, according to Lindstrom, is that none of the foldable acryliclenseswillgothroughanincisionsmaller than 3.5 mm. (they are pliable but not elastic - Editor) In his experience, you have to make one of two compromises if you use an acrylic lens. Either you make the incision larger or make the optic smaller. 3.5 mm instead of 3.2 or 3.0 mm is not a large difference but still, withaclearcornealincision,Lindstromthinks the smaller the incision the safer it is as far as sealingofthewound. Andifyougotoasmaller optics then you get more symptoms of edge glare, particularly with younger patients who have larger pupils.

Edgardo Carreño, M.D., on the other hand, has developed a technique by which he implants the foldable acrylic Alcon AcrySof lens 5.5 mm optic through a 2.75 mm incision. Carreño's technique is described in this book in Chapter 8.

THE FOLDABLE MONOFOCAL

SILICONE IOL's

Second generation silicones are gaining in popularity because they are inert and do not give rise to inflammatory reactions. This second generation silicone polymer is identified as the PDMDPS.

Therewasatimewhenthesiliconelenses caused more inflammation or capsular fibroses but the newer silicones do not do that at least based on the studies made by Lindstrom and others. Many surgeons like silicone lenses because they go through an incision smaller than other lenses thereby allowing a larger optic. The favorite lenses are those with 6.0 mm optic or larger.

There are now two companies that have a 6.3 mm optic silicone lens. One of them is

Staar and the other is Bausch & Lomb. Most other companies have 6 mm optic silicone lenses. The most popular monofocal foldable silicone lenses are Allergan's SI 40 NV and Bausch & Lomb's LI 61 both of which have a 6 mm optic. The Bausch & Lomb LI 63 silicone lens has a 6.3 mm optic. Silicone lenses have more elasticity. When the lens is implanted through an injector, it stretches. So it can go through a smaller incision. The AllerganSI40NVthathasa6.00mmopticand the Bausch & Lomb LI 63 with a 6.3 mm optic will go through a 3 mm incision with the proper

(Fig. 132). This gives you a 6.3 mm or 6.0 mm optic through a 3 mm incision. The open modified C loop silicone lenses are better accepted by the surgeon than the plate haptic lenses because of less decentration.

The Importance of Cost

An additional advantage of the silicone lenses is that because many companies make them, they tend to be less expensive. And so, if you are in an environment where cost is an issue, which is just about anywhere in the world, the new second generation, high quality siliconelensesontheaveragecanbepurchased for maybe half the price of foldable lenses of other materials.

OTHER MONOFOCAL LENSES

The Hydrogel, Foldable Monofocal

IOL

These lenses swell in water. Their mechanical properties are pliable rather than elastic. Their properties are close to PMMA but have a hydrophilic surface and may be folded and inserted through small incisions.

The Foldable Toric Lens

The STAAR toric IOL (AA4203T) combines recent toric technology with a flexible optic. The toric optic offers three cylindrical powers (2.5 D, 3.5 D, 4.0 D) as well as spherical (+14D to +26 D) values, and the plate haptic possesses large fenestrations designed for lens fixation in the capsular bag.

The results of this product are encouraging and appear to be stable. This implant extends the range of refractive lens surgery, especially in cases where high ametropia is combined with astigmatism.

Bitoric Lens But Not Foldable

Although we here emphasize essentially the trends towards the increasing use of foldable lenses, it is important to bring out the development of the bitoric IOL although it is not foldable. This lens has been developed by H.R. Koch and manufactured by Dr. Schmidt Intraokularlinsen in Germany. The diskshaped PMMA implant consists of two toric lenses of the same power, both with one planar and one toric side, which counter-rotate to produce a variable degree of astigmatic power. The direction of the haptic defines the position of the cylindrical axis, and two additional lines in the optical periphery allow an

exactintraocularpositioning. Therangeofthis 6mmtoricIOLisoutstanding:sphericalpower between -3.0 D and +30 D combined with cylindrical power from +1.0 D to +12.0 D. It is 12.5 or 13.4 mm in diameter;

THE FOLDABLE

MULTIFOCAL IOL

The Array Multifocal Silicone

Lens

This is one of the most important developments in rehabilitation of sight and improv-

Figure 131 (right): How the Multifocal Array Intraocular Lens Works - Cross Section View

This cross section shows how the steeper areas of the lens (yellow zones 2 and 4) are of higher power and focus on near objects (N). The flatter areas of the lens (red zones 1, 3, and 5) are of lower power and focus far objects

(F). Light rays from a distant object (O) which refract through zones 2 and 4 (yellow rays) focus at (N). Light rays from a distant object which refract through zones 1, 3 and 5 (red rays) focus at (F). Zones 2 and 4 have smooth transitions to adjacent zones, and focus light at intermediate distances. These aspheric transitions between the optical zones greatly reduce the halo effect which was sometimes bothersome using older diffractive designs.

ing the quality of life following cataract surgery. I. Howard Fine, M.D., and Richard Hoffman, Javitt and colleagues in the U.S. and Virgilio Centurion, M.D. in Brazil have done extensive clinical research on the performance of this foldable multifocal lens and the benefits of high quality multifocal vision in their patients. Having used different kinds of multifocal IOLs in the past, Centurion is familiar with the complications in their design. This new multifocal lens, however, is a refractive molded lens instead of a diffractive lens (Figs. 130, 131). Its use is recommended by Centurion for surgeons who are confident with phacoemulsification and small incision techniques.

Figure 130 (left): How the Multifocal Array Intraocular Lens Works - Frontal View

The new multifocal Array intraocular lens has five refractive zones on the anterior surface. Betweeneachofthemthereisanarrowaspherictransition zone. Zones 1, 3 and 5 (red) dominate for distance vision, and zones 2 and 4 (yellow) dominate for near vision. The optical mechanism of these zones is shown in Fig. 131.

How Does the Array Foldable Multifocal Lens Work?

The lens is manufactured by Allergan Medical Optics. It has a foldable silicone optic that is 6.0 mm in diameter with haptics made of polymethylmethacrylate and a haptic diameter of 13 mm (Fig. 130). The lens can be inserted through a clear corneal or scleral tunnel incision that is 2.8 mm wide, using the Unfolder injector system manufactured by AMO (Allergan) (Fig. 82 A).

There are five zones on the anterior surface. Between each of them there is a narrow aspheric transition zone. The 5 dominant zones provide the following: 1) a clear image for distance (2 zones); 2) one zone for intermediate distance, and 3) two zones for near. The Allergan Array Lens differs from the older diffractive lens designs not only in having classical optics for the definitive zones, but in having aspheric transition zones which, according to Centurion, provide the patient with a smooth transition between the images for distance, intermediate, and near vision, greatly reducing the halo effect which was sometimes so bothersome with older designs. Even those patients who may complain of some halos after surgery seldom report them 2 or 3 months later.

Fine and Hoffman describe the lens as having an aspherical component and thus each zone repeats the entire refractive sequence corresponding to distance, intermediate, and near foci. This results in vision over a range of distances. The lens uses 100% of the incoming available light and is weighted for optimum light distribution. With typical pupil sizes, approximately half of the light is distributed for distance, one-third for near vision, and the remainder for intermediate vision.

Quality of Vision with Array Multifocal

Refractive multifocal IOLs, such as the Array, have been found to be superior to diffractive multifocal IOLs by demonstrating better contrast sensitivity and less glare disability. The Array does produce a small amount of contrast sensitivity loss equivalent to the loss of 1 line of visual acuity at the 11% contrast level using Regan contrast sensitivity charts. This loss of contrast sensitivity at low levels is present only when the Array is placed monocularly. This has not been demonstrated with bilateral placement and binocular testing. In addition to relatively normal contrast sensitivity, good random-dot stereopsis and less distance and near aniseikonia were present in patients with bilaterally placed implants as compared to those with unilateral implants.

In a study by Javitt and colleagues, 41% of bilateral Array subjects were found never to require spectacles, as compared to 11.7% of monofocal controls. Overall, subjects with bilateral Array IOLs reported better overall vision, less limitation in visual function, and less use of spectacles than did monofocal controls.

Studies in different parts of the world report that more than 85% of patients have 20/40 or better vision without correction after implantation with this lens. All of the 456 patients in the US Clinical Study have J3 or better, and more than 60% are J2 or J1 without correction. About half are 20/20 without correction.

Patient Selection and Results

Fine and Hoffman emphasize that the advantages of astigmatically neutral clear

corneal cataract surgery have allowed for increased utilization of multifocal technology in both cataract and clear lens replacement surgery. Careful attention to patient selection, preoperative lens power calculations, in addition to meticulous surgical technique, will allow surgeons to offer multifocal technology to their patients with great success.

Researchers working with this lens have the clinical impression that depth of focus and quality of vision are improved if the surgeon does a bilateral implantation and implants the second eye within 4 weeks of the first implantation. The results seem to be improved if there is a very short interval between the first and second eye. (If the cataract merits removal in both eyes. This is usually the case when modern small incision cataract surgery is performed. - Editor).

Of the 350 multifocal lens implantations Centurion has done, about half were bilateral, and half were monocular. The monocular implantations involved traumatic or inflammatory cataracts rather than senile cataracts . He has not yet used multifocal IOLs in patients with congenital cataracts, but they work well for monocular implantation when a patient has one normal eye. Generally patients do not depend upon glasses much for near vision after the implantation. With bilateral implantation, the quality of vision and quality of life of patients improve considerably. Sometimes they only need glasses to drive at night and to read very small print.

Fine and Hoffman point out that the most important assessment for successful multifocal lens use, other than patient selection, involves precise preoperative measurements of axial length in addition to accurate lens power calculations. They have found applanation techniques in combination with

the Holladay II formula and the Holladay II back-calculation to yield accurate and consistent results.

Specific Guidelines for Implanting the Array Lens

Fine and Hoffman have used the Array multifocal IOL over the last 2.5 years extensively, in approximately 30% of their cataract patients and in the majority of their clear lens replacement refractive surgery patients. As a result of their experience, they have developed specific guidelines with respect to the selection of candidates and surgical strategies that enhance outcomes with this IOL.

AMO recommends using the Array multifocal IOL for bilateral cataract patients whose surgery is uncomplicated and whose personality is such that they are not likely to fixate on the presence of minor visual aberrations such as halos around lights. Obviously, a broad range of patients would be acceptable candidates. Relative or absolute contraindications include the presence of ocular pathological processes (other than cataracts) that may degrade image formation or may be associated with less than adequate visual function postoperatively despite visual improvement after surgery. Contraindications are age-related macular degeneration, uncontrolled diabetes or diabetic retinopathy, uncontrolled glaucoma, recurrent inflammatory eye disease, retinal detachment risk, and corneal disease or previous refractive surgery in the form of radial keratotomy, photorefractive keratectomy, or laserassisted in situ keratomileusis.

Fine and Hoffman also avoid the use of these lenses in patients who complain excessively, are highly introspective and fussy, or obsessed over body image and symptoms.

They are conservative when evaluating patients with occupations that involve frequent night driving or that put high demands on vision and near work (e.g., engineers and architects). Such patients need to demonstrate a strong desire for relative spectable independence in order to be considered for Array implantation.

In their practice, they have reduced patient selection to a very rapid process. Once they determine that someone is a candidate for either cataract extraction or clear lens replacement, they ask the patient two questions: First, "If we could put an implant in your eye that would allow you to see both distance and near without eyeglasses, under most circumstances, would that be an advantage?" Approximately 50% of their patients say no directly or indirectly. Negative responses may include, "I don't mind wearing glasses," "My grandchildren wouldn't recognize me without glasses," "I look terrible without glasses," or "I've worn glasses all mylife." These patients receive monofocal IOls. Of the 50% who say it would be an advantage, they ask a second question: "If the lens is associated with halos around lights at night, would its placement still be an advantage?" Approximately 60% of this group of patients say that they do not think they would be bothered by these symptoms, and they receive a multifocal IOL.

Centurion also emphasizes that these lenses should not be used in patients with a basic astigmatism of more than 1.50 diopters.

Prof. Luis Fernandez Vega in Spain recommends a series of important guidelines in order to be successful with advanced technology multifocals: 1) Do only bilateral multifocal implantations in adults. Do not place a monofocal IOL in one eye and a multifocal in the other. Otherwise, patients

compare the vision between the two eyes and refer to the differences existing, even though they may have good visual acuity in both. 2) Yes, the multifocal IOL does fullfil its optical purpose both for distance and near. Although it does not completely prevent the wearing of spectacles, it does diminish the dependency on glasses. Clarify this to the patient preoperatively. 3) Select the patient according to his/her visual needs. 4) Do a very precise preoperative biometry; 5) Perfect your cataract surgery to end up with less than 1.00 D astigmatism.

Special Circumstances forArray Implantation

There are special circumstances in which implantation of a multifocal IOL should be strongly considered. Alzheimer's patients frequently lose or misplace their spectacles, and thus they might benefit from the full range of view that a multifocal IOL provides without spectacles. Patients with arthritis of the neck or other conditions with limited range of motion of the neck may benefit from a multifocal IOL rather than multifocal spectacles, which require changes in head position. Patients with a monocular cataract who have successfully worn monovision contact lenses should be considered possible candidates for monocular implantation. The same is true for certain professionals such as photographers who want to alternate focusing through the camera and adjusting imaging parameters on the camera without spectacles. In these patients, the focusing eye could have a monofocal IOL and the nondominant eye a multifocal IOL. Fine and Hoffman almost always use the Array for traumatic cataracts in young adults in order to facilitate binocularity at near,

especially if the fellow eye has no refractive error or is corrected by contact lenses.

Need for Spectacle Wear PostOp

Prior to implanting an Array lens, they inform all candidates of the lens's statistics to ensure that they understand that spectacle independence is not guaranteed. Approximately 41% of patients implanted with bilateral Array IOLs will never need to wear eyeglasses, 50% wear glasses on a limited basis (such as driving at night or during prolonged reading), 12% will always need to wear glasses for near work, and approximately 8% will need to wear spectacles on a full-time basis for distance and near correction.

Halos at Night and Glare

15% of patients were found to have difficulty with halos at night, and 11% had difficulty with glare, as compared to 6% and 1%, respectively, in monofocal patients.

SURGICAL PRINCIPLES AND GUIDELINES FOR IOL IMPLANTATION

Just as there are a large number of methods to disassemble the nucleus there is a wide variety of techniques to implant the IOL's, particularly the foldable lenses. What counts is the results and the feasibility to achieve a successful implantation.

We present here the surgical principles and guidelines for implantation of the most commonly used types of foldable lenses. We have chosen the principles followed by highly respected, skilled phaco surgeons who do a great deal of teaching in addition to having a large, solid practice in different

geographical and cultural regions. They have provided HIGHLIGHTS with the pearls of the methods that lead them to successful implantation. They are: Jack Dodick, M.D., from New York, I. Howard Fine, M.D., from Oregon, and Richard Lindstrom, M.D., from Minnesotta, three different areas of the United States. And Edgardo Carreño, M.D., from South America (Chile).

First, you will find the present status of the preferred methods of lens implantation, forceps vs injectors, their pros and cons. Second, the techniques of implantation of 1) the Array Multifocal Foldable Lens

(Allergan). 2) The acrylic monofocal lens, in this case the AcrySof Lens (Alcon). 3) The silicone monofocal foldable lens (STAAR).

PREFERRED METHODS OF IOL IMPLANTATION

Use of Forceps vs Injectors

Advantages and Disadvantages

Many surgeons like to use forceps to implant the foldable lens, others use injectors. Lindstrom reminds us that the original instruments available for foldable lenses were all forceps. Consequently, those surgeons that used foldable lenses early on got used to the forceps insertion method (Figs. 133, 134). But there is a disadvantage to the forceps approach. It adds some mass to the amount of material you are putting into the eye (Fig. 132) thereby requiring a slightly larger incision. Another disadvantage of using forceps is that you may touch the lens to the conjuntiva or sclera before placing it into the incision. Several studies have shown that the lens picks up bacteria and mucus and

other debris from the surface of the eye when you use the typical cross action forceps (Fig. 133). This may increase the risk of postoperative inflammation or infection. For these reasons, Lindstrom now prefers the injectors, because you take a sterile lens out of a sterile package, put it into a sterile injector and place the lens directly inside the eye. With the injector you also have less bulk, thereby requiring a slightly smaller incision (Fig. 132-A).

The reason a good number of surgeons do not like the injectors is: 1) they got used to folding with forceps, (Figs. 132-B, 133) which are convenient and they are used to them. 2) All the injectors have a small failure rate. It is very annoying when you load a lens into the injector and then after placing it inside the eye, the optic is torn or one of the lens loops is bent or damaged. Some surgeons do not use injectors because they do not like the lens failures that occassionally occur with them. The newer injectors of the better companies, however, are performing very well now.

New Trends for Folding and Insertion of IOL's

The majority of lenses are still folded and inserted with forceps (Figs. 132-B, 133). Nevertheless, there is a definite trend toward the development of separate instruments for folding and inserting IOL’s rather than using the insertion device to fold the IOL. The combination of instruments designed by the manufacturers to facilitate folding and insertion is known as cartridge injector systems which are then used to implant the IOL.

Cartridge Injector Systems

Fine, Lewis and Hoffman believe that there are many perceived advantages of implanting foldable IOLs with injector systems, as compared with folding forceps. These advantages include the possibility of greater sterility, ease of folding and insertion, and implantation through smaller incisions as emphasized by Lindstrom (Fig. 132).

Greater sterility with injector systems is believed to occur because the IOL is brought directly from its sterile package to its sterile cartridge and inserted into the capsular bag without ever touching the external surface of the eye, as is the case for lenses in folding forceps. Although this advantage would suggest a lower rate of endophthalmitis with injector systems, recent clinical studies have shown no significantly different rate of bacterial contamination of the anterior chamber after implantation of silicone lenses with a forceps versus an injector.

Perhaps the most appealing advantage of injector systems is that the lens can be loaded by a nurse or technician without the use of an operating microscope, further streamlining the procedure. Inaddition,insertingfoldablelenses with a cartridge device is generally felt to be easier than insertion with forceps.

There are no irregular surfaces as may occur between the surface of the forceps and the lens. The IOL is lodged inside the cartridge and injector system.

Allergan's foldable three piece silicone lens (monofocal or multifocal - AMO Array) with PMMA haptics may be implanted with AMO's Unfolder Phacoflex injector system. Allergan's acrylic foldable IOL (Sensar and Clariflex lenses) may be implanted with a new

injector now available and known as the

Unfolder Sapphire, as described by Centurion (Fig. 82-A). These injectors are resterelizable (as are the forceps, of course).

Alcon’s popular 5.5 mm AcrySof IOL may be implanted with one of its injectors such as the Monarch (Fig. 82) or with a standard cartridge through a 3.4 mm incision. Carreño reports injecting this lens through a 2.8 mm incision(Fig.132). ManysurgeonsuseAlcon’s Acrypack (Fig. 82) when implanting the AcrySof lenses. The Acrypack serves to first fold the IOL. The surgeon then uses a forceps (Fig. 81) to implant the already folded IOL.

The AlconAcrySoflens, which requires 3.5 to 4.0 mm incisions for 6.0 mm optics and

3.2 to 3.5 mm incisions for 5.5 mm optics, when implanted with forceps is now packaged in a wagon wheel dispenser. The easiest folding instrument to use for these lenses is the Rhein folder, as recommended by Fine because the tips have been extended to make it easier to remove the lens from its wagon wheel packaging. The forceps can be turned with the tips down in the nondominant hand. The tips go into the slots on both sides of the optics, so that the lens can be picked up and placed on a drop of viscoelastic. The forceps are then turned so that the tabs are down. The lens is grasped and folded, and then the insertion device is used to insert the lens using the surgeon’s dominant hand.