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

Modern cataract surgery is definitely related to lens removal through small, short, valve like incisions and implantation of foldableintraocularlensesimplantedthroughthese short incisions.

Tackling the Challenges

In this Volume we present what is best for our patients and how to tackle the challenges with vigor. We present the new developments in preoperative evaluation, the expansion of the indications as the outcomes have improved, the new, sometimes complex problems brought by refractive and vitreoretinalsurgeryincalculatingIOLpower. Andweillustrate thestepsthatremainrather constantand which apply either to the surgeon in the process of transition or the experienced small incision surgeon, vs the methodsthatdo change and require the skill of an experienced surgeon.

We also present the anesthetic methods of choice, the understanding of the phaco machine, how it works and what the rationale is behind its optimal use. How to undergo the safe and successful transition from planned extracapsular to phaco. The incisions of choice for most surgeons, the methods that enhance the performance of capsulorhexis in complex cases, the modern techniques of hydrodissection, hydrodelineation and cortex removal that have stood the test of time and the advantages and disadvantages of the different methods of nucleus removal in phacoemulsification.

Role of Small Incision Manual

Extracapsular

Although we provide special emphasis on how to master phacoemulsification and foldable IOL implantation, including an indepth analysis of how to prevent and manage intraoperativeandpostoperativecomplications, wealsopresenttoyouthesmallincisionmanual extracapsular techniques of proven and lasting value. For those surgeons who are prevented by practical considerations, or who simply prefer to not take the significant step of entering into small incision surgery, the chapter on how to perform a flawless planned extracapsularwith8mmincisionanditsmeritsissuperbly as presented by one of the world's master surgeons.

IOL's of Choice

In modern cataract surgery it is essential to discuss the IOL's of choice and their merits. Selectingthecorrectlensimplant(sizeofoptic, chemical material, foldable vs non-foldable, mono vs multifocal) may play a more important role in the final patient's final visual outcome and satisfaction than the specific technique used for phacoemulsification of the nucleus.

The Best Phaco Technique

The best phacoemulsification technique to use is based on the relation of the type

of cataract to a specific method of nucleus removal for that specific stage of cataract. The divide and conquer in four quadrants continues to be the procedure of choice for the beginner in the transition period or for the surgeon who does not have a large volume of cataract surgery. The technique for nucleus removal with one hand continues to be fundamental for each phaco surgeon to learn. We will also present the phaco sub-3, phaco chop, phaco pre-chop, choo-choo chop and flip and the phaco burst, all of which are techniques for the more advanced or experienced surgeons. Each has its merits, effectiveness and limitations.

The Complex Cases

Small incision cataract surgery has significantly changed the approach and management of the complex cases. It is the most important contribution made in years to a successful and safe combined glaucoma-cataract

operation, to management of traumatic cataracts and cataract surgery in patients with corneal dystrophies.

Pediatriccataractshavenotbeenresolved with the improved management options and almost risk-free capabilities of the magnitude that we have available in adult patients. This, in part, may be related to the fact that the postoperative care depends more on the parents than on the surgeon. The previously highly controversial point of implanting intraocular lenses in children has shifted to a positive decision on the part of most surgeons who now agree to implant IOL's in children when the selection of cases has been done prudently.

Let us now proceed to discuss each one of the highlights of modern cataract surgery. The field is exciting and a source of great satisfaction to the surgeon who does it well and with full dedication to the benefit of his or her patients.

ClinicalApplications-Behaviour

of Different Cataracts

Understanding the three-dimensionality and concentric anatomy of the lens as originally conceived by Henry Clayman, M.D. for HIGHLIGHTS is fundamental for having a clear picture of some of the main steps in performing phaco. I refer to the dissection of the different structures of the nucleus with fluid, that is, hydrodissection of the anterior and posterior capsule from the cortex, separation of the nucleus and epinucleus with fluid and the different tissue reactions to the forces presented during phacoemulsification of the nucleus.

The normal crystalline lens is an avascular structure. As pointed out by Howard Gimbel, M.D., lens fibers are surrounded by the lens capsule which is the basement membrane of the lens epithelial cells (Fig. 1). Lens epithelial cells are located just inside the capsule and exist as a single layer. The epithelial cells can differentiate into lens fibers, and this process occurs in an area just posterior to the lensequator. Asnewlensfibersareformed,the central fibers are compacted, forming the nucleus of the lens. The surrounding densely packed fibers form the cortex (Fig. 1). Due to the anatomical arrangement of cells and fibers, the Y sutures are formed within the lens nucleus.

For a surgeon not experienced in small incision extracapsular techniques, there may be difficulties recognizing the hidden anatomy of the morbid cataract. It may be difficult to

distinguishwhatisreallyanteriorcapsule,what is cortex and where the posterior capsule is.

Whenremovingthecortex,wemustkeep in mind that its substance is three dimensional (Fig.1). Asdescribedinthisfigure,thenucleus is the pit of the avocado. The pit in the avocado does not drop out because it is held in by adhesionsbetweenthefleshoftheavocadoand the pit. Figure 1 also shows that the cortex (C) adheres to the epinucleus and the nucleus. In order to remove the nucleus by whatever technique you prefer, these nuclear-cortical adhesions have to be broken and out comes the nucleus, whether by phacoemulsification or by planned extracapsular.

The residual cortex, which is the flesh of the avocado, is wrapped around, three dimensionally, inside the skin of the avocado, which is the capsule (Fig. 1). When aspirating the cortex,itisprudentnottoattackthecortexright on but to get a free edge, which you may attract to the aspiration port, and peel from its capsule support.

In Fig. 1 you may see a conceptual cross section of the anterior globe, with all the structures of the human lens involved in the maneuvers hereby described. The capsule is like the skin of an avocado, both anterior (A) and posterior (P). The flesh of the avocado is comparable to the cortex (Fig. C). The pit of the avocado is comparable to the lens epinucleus and nucleus (Fig. E-N). In (1) the cortex (C), epinucleus (E) and nucleus (N) are shown removed from the capsule. (2) Shows the cortex (C) removed from the nucleus and epinucleus (E and N). The nuclear-cortical

adhesions have to be broken down before the nucleus can come out (2 and 3). In (E) the epinucleus is shown as an, entity distinct from thenuclearcore. Thisfigureallowsustobetter understand the anatomical basis for the formation of grooves across the nucleus skillfullyutilizedbythesurgeon inthetechniqueof phacoemulsification.

Anatomical Characteristics of

Different Types of Cataract

The lens in cross section is made up of a concentric series of elliptical rings. Each one of these rings represents growth of the lens and the laying down of additional lens material from the epithelial cells located on the underside of the anterior capsule. In soft to medium density cataracts, the concentric lamellae of cataract tissue are not densely packed, so much of the space inside the cataract is taken up by

Figure 2: Dense, Nuclear Brunescent

Cataract

In dense, nuclear brunescent cataracts, as shown in Fig. 2, there is less water content, the capsule is dehydrated and there is a significant increase in the density and opacity of the nucleus (C). These nuclei are more like rocks, and are the hardest to manage with phacoemulsification in the transitional stage or by surgeons inexperienced in phaco. Difficulties during surgery may arise that can be characteristic in this type of cataract such as difficulty in identifying the capsulorhexisorwiththehydrodissection.

moisture. Medium to firm-density cataracts have concentric lamellae of tissue that are densely packed together, packed so tight that there is no room for moisture between lamellae.

How Cataracts Respond Differently

Paul Koch, M.D. emphasizes that each one of these different types of cataracts responds differently, so surgical forces need to be applied differently. In breaking the nucleus the surgeon needs to individualize the operation to take advantage of the natural tendencies of each type of cataract. Soft to medium density cataracts are malleable and compliant. We can hold them in the capsular bag and squeezethemfrombetweenneighboringpieces.

Medium to firm density cataracts are more likerocks. Theyhaverigidform and aremuch more demanding of the surgeon's skill. If we

rub them against the capsule, the capsule can break. If we pull them up into the anterior chamber, the capsulotomy may split. If they touch the corneal endothelium, they abrade it.

Understanding this surgical anatomy of the lens and its clinical applications helps significantly in recognizing that each type of cataract acts differently and that our approach should vary depending on the individual patient (Fig. 2).

INCIDENCE AND

PATHOGENESIS

It is widely known that cataracts constitutethemajorsourceofcurableblindnessworldwide. Not only do they seriously affect large segments of the population in developing or less economically fortunate regions but also the peri-urban areas of large and developed cities which are equipped with highly trained ophthalmologists and the latest technology. For psychological or social reasons difficult to understand, many blind or almost blind persons living in these peri-urban "belts" do not seek medical advice and treatment when easily available. This is one of the mysteries of people whose quality of life is significantly limited by partial or complete opacification of the crystalline lens. Figure 2 shows a brunescent, advanced, hard cataract which becomes sometimes very difficult to treat by phaco, even in skillful hands. Many patients allow their cataracts to become this much advanced even if they live near medical facilities that may provide proper care at a much more advantageous time.

AspointedoutbyHowardGimbel,M.D., there are a variety of causes and types of cataracts. By definition, all cataracts share the common feature of opacification of some portion of the crystalline lens which, if within the to cataract formation.

BIBLIOGRAPHY

Assia, EI., Legler, UFC., Apple, DJ.: The capsular bag after short and long term fixation of intraocular lenses. Ophthalmology, 1995; 102:1151-7.

Boyd, BF.: Cataract/IOL Surgery. World Atlas Series of Ophthalmic Surgery, published by HIGHLIGHTS, Vol. II, 1996; 5:5-13.

Boyd, BF.: Cataract/IOL Surgery. World Atlas Series of Ophthalmic Surgery, published by HIGHLIGHTS,Vol. II, 1996; 5:34-38.

Boyd, BF.: New developments for small incision cataract surgery. Highlights of Ophthalm. Journal, Volume 27, Nº 4, 1999;45-46.

Gimbel, HV., Anderson Penno, EE: Cataracts: Pathogenesis and treatment. Canadian Journal of Clinical Medicine, September 1998.

Koch, PS.: Simplifying Phacoemulsification, 5th ed., published by Slack; 1997; 7:85-86.

Lens and Cataract, Basic and Clinical Science Course, Section 11. American Academy of Ophthalmology, 1998-99.

INDICATIONS

To date there is no established medical treatment for the prevention or treatment of cataract formation and thus the treatment of cataracts remains surgical. Contrary to the commonly held belief that cataracts must reach a certain degree of density or become "ripe" prior to considering cataract surgery, today the crystalline lens can be removed at virtually any stage. In fact, refractive lensectomy in which the clear crystalline lens is removed may be used to surgically eliminate or significantly reduce the need for glasses in patients with very high myopia or hyperopia. In the latter condition, this may be achieved by implanting several piggyback lenses within the capsular bag following clear lensectomy.

Role of Quality of Life

Cataract/IOL surgery improves quality of life better than any other medical procedure known to mankind. Cataract surgery is indicated when the patient's quality of life is being affected by visual impairment, when there is a diminution in vision if the patient is exposed to light or at night, and when the preoperative evaluation indicates that the potential for restoration of sight is good. How much a patient's quality of life is impaired from a cataract is relative, varying with the patient's occupation and age. The key factor is not to wait until a nuclear cataract becomes hard. With time, the lens fiber density becomes a hard nuclear brunescent cataract (Fig. 2) . With most modern phacoemulsification techniques it may be-

come increasingly difficult to perform surgery if the lens becomes extremely dense or brunescent.

Waiting too long may require that the surgeon operate on dense nuclear cataracts, which increases the risk of posterior capsule tears, whether we perform planned extracapsular or a phacoemulsification. This complication may lead to other rather serious problems such as dislocated nucleus, retinal detachment, macular edema, bullous keratopathy and inflammation.

The Role of Visual Acuity

There are very few strict criteria for recommending cataract surgery. In the United States, however, many professional review organizations have indicated that the reduction of Snellen distance acuity to 20/40 or worse as a result of cataract is sufficient indication in and of itself for cataract surgery. This is generallytheminimumstandardfordriving. In some of the advanced, developed countries, being unable to obtain a driver's license may seriously affect a person's life because he/she may be disqualified to drive to the market or shop to purchase food and other materials essential to daily existence. However, in many cases surgery may be indicated without reduction of visual acuity to the level of 20/40 if the patient has difficulty performing activities of daily living. Because patients have varying occupational and recreational needs, some patientsmayneedcataractsurgerypriortohaving their vision reduced to 20/40 by standard tests. In addition, near vision in some cases may be

compromised more than distance acuity particularly in the case of central posterior subcapsular cataracts. The trend toward early removal of cataract offers the advantage of operating on a younger age group, many of whom are still productive members of society. Their need for early return to their usual lifestyle is extremely important. The older population, often living alone, also benefits from early visual recovery. These high expectations and needs require that the ophthalmic surgeon perform superior surgery to obtain excellent postoperative visual acuity and early visual rehabilitation.

Asemphasizedby Gimbel,symptomsof cataracts include complaints of a yellowing of vision,glare,halos,decreasednightvision,and generally blurred vision in adults. Nuclear sclerosis which is a typical form of age-related cataracts may also induce a myopic shift and patients may give a history of having changed their glasses several times within a short period of time. In children cataracts may present as leukocoria and may result in strabismus and/or amblyopia if not treated promptly.

Contrast Sensitivity and Glare

Disability

In evaluating a patient with cataract and in the process of deciding when that person requires cataract/IOL surgery, it is fundamentaltokeepalwaysinmindthatstandardSnellen acuity measurements do not give any information with regard to symptoms of disabling glare. As a matter of fact, very good visual acuity with the Snellen chart in the physician's examining room may lead the ophthalmologist to making the wrong decision and recommendations unless he or she takes other factors into consideration. In later years, we have become

increasingly aware that diminished contrast sensitivity which interferes with sharp vision under different color backgrounds or target luminance, is an essential element of sight and a highly limiting factor in the presence of cataract. This is perceived by the patient for example when he or she is unable to read a computer screen at the airport if the backgroundislightblueand theprintislight yellow even though visual acuity in the physician's refracting lane was 20/30 or 20/25. The same for disabling glare.

These are two additional very important issues in determining when the cataract should be removed. For many years this judgment has been based on Snellen visual acuity. But a patient can score quite well on Snellen acuity while suffering in real life. Posterior subcapsular cataracts are notorious for interfering with reading, even when distance vision is good, and may induce a great deal of glare. Snellen acuity may be 20/20 or 20/25, but against oncoming headlights while driving at night, for instance, the glare may diminish the functional vision to 20/100 or even 20/200. People with nuclear sclerosis, the most common form of cataract, tend to be bothered by decreased contrast sensitivity rather than glare.

Although glare disability and contrast sensitivity are distinctly different, the terms often are erroneously interchanged. The testingcharacteristicsofeach,however,mayoverlap, and a reduction in one function often leads to a diminution in the other, further adding to the confusion of their differences. As clarified by Samuel Masket, M.D., glare disability is a light-induced visual symptom. Contrast sensitivitytestingisameansofvisionanalysis, analogous to a markedly expanded form of Snellen acuity evaluation at varied amounts of target luminance.

Contrast Sensitivity

Characteristics

Like audiometry, which measures the sensitivity of the hearing apparatus to stimuli at different audio frequencies, contrast sensitivity analysis determines the ability of the visual system to perceive objects of differing contrasts as well as sizes.

A patient who has a reduction in contrast sensitivity might perceive the small, highly contrasted targets on a Snellen test line but be incapable of identifying larger objects at reduced contrast. There are alterations in the visual system that can cause visual loss that are not detected by the determination of Snellen visual acuity but may be evaluated by testing of contrast sensitivity function. This is unlike

Figure 3 A (above left): Importance of Testing for Contrast Sensitivity

The Contrast Sensitivity Test is used clinically to evaluate cataracts, glaucoma, diabetic eye disease, contact lens performance and refractive surgery. In the presence of cataract the clouding of the lens causes light scatter on the retina. This reduces image contrast and causes dimness of vision. One of the more difficult problems in evaluating how a cataract is affecting the patient's visual function is that many cataract patients preserve good visual acuity as tested in the refracting lane (Snellen chart) but complain about their visual disability. The true “real-world” vision of cataract patients can be established as a functional acuity score using contrast sensitivity and glare testing.

Figure 3 B (below right): Contrast Sensitivity Recording Chart

The contrast sensitivity recording chart provides four (4) rows of wave gratings.At the recommended test distance of 8 ft (2.5 meters), these gratings test the spatial frequencies of 3, 6, 12 and 18 cycles/degree. This chart provides a full contrast sensitivity curve. The functional acuity is determined by the lowest level of contrast sensitivity (gray band) that can be detected by the patient. The functional acuity score is shown in a bracket next to the contrast sensitivity score.