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

Making Patients Confident

From the minute the patient considers undergoing surgery, fear is present. There is fear of the unknown and fear of someone operating on your eye. Jack Dodick, M.D., from New York, believes in the important influence of office personnel and environment on makingpatientsconfidentandcomfortable. Dodick strongly advocates hiring and training highlevel professional staff. When patients interact with highly competent staff at every encounter, they tend to conclude that the doctor must be very good because he has selected and trained his staff so well. Many doctors pay too little attention to the impressions staff make on their patients. They are tempted to cut corners by hiring clerks at low pay if they fail to realize that patients’ impressions of staff are integral to their impressions of their physician.

In addition, the office environment should be tasteful. The impression patients have when they enter the office influences their feelings about their physician. An office that is dirty and cluttered reflects poorly on the practice. Dodick believes that once patients feel respected and comfortable with the expertise of the physician and his/her staff, they relax and decide they have come to the right place.

Patients Encounter with the Physician

And in the encounter with the physician patients should feel respected and important. Even though the waiting room is busy, everything should seem unhurried when the patient is sitting in the chair across from the physician. The ophthalmologist should convey the impression that, at this time, the patient is the most important person.

The physician’s ability to project a confident manner is also critical to success. Dodick believes it is an art to convey this confidence and professionalism to patients. It is partly done through certain inflections in the voice; perhaps it is easier to explain in reverse. Sometimes the doctor who does not feel totally secure in his ability to produce results may become a little defensive, and give more emphasis to potential complications than the real positive benefits of the operation. “Well, you have a cataract. As you know, you can have it operated on or not, and there are some complications that sometimes occur. For example. . .” Although potential complications are in fact true, the chance that these complications will occur is minimal. Dodick does not dwell on these rare potential complications. Instead, he emphasizes the

very high probability of positive results when communicating with patients. He retains a position of objectivity in order that his own perspective will not unduly influence the patient. The patient must be informed of potential risks but with modern small incision cataract surgery, they are very unusual.

Ingredients of a Strong Relationship

The physician’s ability to instill confidence and trust in patients, and an ability to articulately convey his confidence through the spoken word are the basic ingredients of a strong relationship between physician and patient.

A fundamental question is how should the ophthalmologist approach patients who measure well on Snellen acuity, but still complain about their vision because of the very important factors of contrast sensitivity and glare we have already discussed. Dodick follows these basic steps. He first listens to the patient and tries to make a historical determination about how happy or incapacitated they are because of their vision. If patients claim to be very happy with their vision, Dodick goes no further. He merely instructs them that they, like everyone over 50, have some lens changes. He explains the basic anatomy of the human eye (Fig. 1-A), with its clear windows inside and outside, and the tendency of the inside window to become cloudy. The treatment, of course, is to replace the cloudy window with a clear window and thereby restore their vision.

In approaching the question of when a cataract should be removed, Dodick reinforces the concept that in nearly all conditions, cataract surgery is 100% elective. The time to remove a cataract is the time that

patients decide they are unhappy with their vision. Most people understand this, but often Dodick hears the question, “What would you do in my position?” Dodick handles this by looking the patient in the eye and responding: “This is a very simple question. If I were very happy with my vision right now, I would do nothing. If I were unhappy, I would decide in a minute to have cataract surgery.” Then patients fully realize that cataract surgery is truly an elective procedure.

Evaluating the Patient's Cataract

Of course, giving patients this choice is predicated upon the fact that the ophthalmologist has conducted a thorough examination. With slit lamp biomicroscopy posterior subcapsular cataracts which strongly interfere with vision by inducing a great deal of glare are very easy to evaluate, whereas nuclear sclerotic cataracts are often difficult to evaluate on the slit lamp. People with posterior subcapsular cataracts can measure 20/20 or 20/25 on Snellen acuity because they are really looking through the little pinholes of the posterior subcapsular cages (Fig. 23- A-B). The minute they see oncoming headlights while driving at night, for instance, the glare may diminish their functional vision to 20/100 or even 20/200. On the other hand, people with nuclear sclerosis, the most common form of cataract, tend to complain about contrast sensitivity rather than glare (Fig. 23- C-D).

Over the years Dodick has found that a good way to evaluate lenticular or media changes is to examine the red reflex of the patient by holding an ophthalmoscope about 12 to 14 inches from the eye and determining whether it is a bright red reflex,

or a dark black reflex. This provides a good indicator of opacity. In some circumstances a nuclear cataract can be better evaluated with this technique than with the slit lamp. Dodick does not rely on tests for contrast sensitivity when evaluating cataracts. Although conditions of glare can be simulated in a clinical setting, Dodick relies on the patient’s real life test experience instead.

Approaching the Day of

Surgery

Once Dodick and his patient have reached the mutual understanding that cataract surgery may be beneficial, the patient is in essence turned over to a series of highly trained, dedicated, professional staff who work closely with him. The next person the patient sees is a highly trained technician. The technician explains that a measurement is needed to determine the correct lens to implant into the eye, and they undergo an ultrasonography scan. When the test is completed, the patient is turned over to the surgical counselor, who has become a master at making patients comfortable and ready to approach the day of cataract surgery.

Patient's Expectations

It is essential to clarify to the patient what he/she may expect and what not to expect. Postoperative patient satisfaction is based on this pre-op surgeon-patient communication and understanding. What are the patient's daily needs and what final uncorrected visual acuity for distance and near he would prefer? Does he want to read without glasses? If so, then he must know he would not see perfectly clearly for distance. If he/ she are myopes and consequently read with-

out glasses, by all means do not sacrifice their near vision just for providing 20/20.

The availability of foldable multifocal IOL's makes this surgeon-patient understanding even more critical so that the visual advantages of these lenses need to be fully appreciated versus the disadvantages which exist but may be less significant. A similar situation presents with the alternative of monovision. If the surgeon contemplates using this method, which is a good alternative for many patients, it is important to make sure the patient understands how this works and be enthusiastic with this alternative. Final visual satisfaction with these methods, multifocal IOL's and monovision, will depend a great deal on the selection by the surgeon of the right patient for these alternatives. With multifocal IOL's patients are happier with bilateral implantation. With monocular implantation, it is preferable not to delay surgery in the fellow eye unless there is a major reason, because most patients feel very insecure with monocular vision and having only one eye operated.

DETERMINING IOL POWER (BIOMETRY)

Ocular biometry must be performed prior to cataract surgery. There is no question that when well selected and properly done the ultrasonic methods afford us the best way of achieving the desired postoperative refraction. Determination of intraocular lens power through meaningful keratometer readings and axial length measurement through A-Scan ultrasonography has become a "standard of care". It is a challenging technique and crucial to the visual result and patient satisfaction.

Postop Refractive Errors No

Longer Admissible

This is particularly true considering the high patient's expectations and the minimal astigmatism created by small incision cataract surgery, particularly phacoemulsification. Patients look forward to wearing spectacles postoperatively only under special circumstances. As emphasized by Centurion and Zacharias, postoperative refractive errors are

no longer admissible. In small incision techniques, cataract surgery has attained the status of refractive surgery. Therefore, exact determination of the IOL power to end up with the specific planned postoperative refraction is essential. The advent of multifocal foldable IOL's makes this even more of an important, though complex subject, as well as operating on eyes with different axial lengths: normal (Fig. 24), short as in hyperopia (Fig. 25 A-B), long as in myopia (Fig. 26).

Figure 25 A (above right): IOL Power Calculation in Patients With Very Short Axial Length (Hyperopia)

In eyes with short or very short axial lengths as shown in Fig. 25 the third generation formulas such as Holladay 2 and Hoffer-Q seem to provide the best results. Holladay has discovered that the size of the anterior and posterior segments is not proportional in extremely short eyes (<20.0 mm). Only 20% of short eyes present a small anterior segment (nanophthalmic eyes); 80% present a normal anterior segment and it is the posterior segment that is abnormally short as shown here. (P) represents probe, (S) represents corneal surface.

T H E A R T A N D THE S C I E N C E OF C ATA R A C T S U R G E R Y

Figure 25-B (below left): Concept of the

Piggyback High Plus Intraocular Lenses

In cases of very high hyperopia, a clear lens extraction may be done combined with the use of piggyback high-plus intraocular lenses. One (A), or two (B) or, some surgeons suggest, three or more intraocular lenses can be implanted inside the capsular bag (C). This piggyback implantation technique may solve the problems of having to implant a lens of over +30 diopters with its consequent optical aberrations, but the procedure may give rise to postoperative complications. Some prestigious surgeons have their reservations (see text).

The Challenge of the Complex

Cases

The use of refractive surgery on the cornea using a variety of techniques: excimer (Fig. 27), RK (Fig. 28), Intracorneal Ring Segments (INTACS - Fig. 29) makes ocular biometry even more complex. These refractive corneal refractive techniques change the parameters in these special cases as compared with those we use for normal eyes and make these special cases. Computerized videokeratography provides additional important data.

The current acceptance of implanting IOL's in children following pediatric cataract surgery (Fig. 31) and the frequent use of vitrectomy with the use of silicone oil

(Fig. 32) frequently in Europe and infrequently in the U.S., also add unique and different difficult challenges, in performing an exact biometry in every individual patient's condition. When using ultrasound, axial length is determined by measurement of the reflection of the eye tissue interfaces with the ultrasonic beam (Fig. 24 - arrows). The A-scan must be carefully calibrated and the beam velocity must correspond to whether or not the patient is phakic, pseudophakic, or aphakic and may need to be modified in the special cases previously described. The ultrasound probe (T) has a piezoelectric crystal that electro-mechanically emits and receives high frequency sound waves. The sound waves travel through the eye until they are reflected back by any structure that stands in

their way (represented by arrows). Assuming the average velocity of the sound waves in the eye being measured, and based on the time it takes for the sound waves to travel back to the probe (arrows), a distance can be calculated. The ultrasound equipment's computer can automatically multiply the time by the velocity of sound to obtain the axial length. At least three scans should be obtained which are within 0.15 mm of each other. Gimbel recommends that the A-scan should be measured twice by independent technicians if the axial length is unusually short (Fig. 25) (hyperopia) or long (Fig. 26) (myopia) (<22 mm or >25 mm), or if the difference between the two eyes is more than 0.3 mm, if the axial length measurement does not correlate with the refraction or the patient has difficulty with keeping the eyes open or with fixation.

The Most Commonly Used Formulas

The most commonly used IOL formula was developed by Sanders, Retzlaff and Kraff and is known as the SRK formula, where p = A - 2.5L - 0.9K. "P" refers to lens implant power to produce emmetropia, "L" refers to axial length, "K" refers to average keratometric readings in diopters and "A" is a constant that is specific to the lens implant that is to be used. Several second and third generation lens power calculation formulas have been developed including the SRK2 and SRK/T, Hoffer Q, and the Holladay 2 formulas. Gimbel emphasizes that to avoid errors in lens power calculations not only must the biometry be accurate and the correct "A"

constant used, but also the estimated anterior chamber depth (depending on the formula), preop refraction and age must be taken into account. Adjustments can also be made for a specific surgeon's technique.

In the search for continuous refinement and accuracy of results, new methods based on laser interferometry may replace ultrasonography in the future.

Main Causes of Errors

Zacharias and Centurion have pointed out that most postoperative refraction errors occur not due to errors in the formulas but to imprecise preoperative measurements. For each millimeter of error in biometry there is a -2.5 diopter error in the calculation of the IOL power. If more than one error occurs in the same examination there may be significant postoperative refractive errors. Keratometry in both eyes should be repeated when:

•corneal curvature is less than 40.00 D or more than 47.00 D;

•the difference of the corneal cylinder is more than 1.00 D between both eyes;

•the corneal cylinder correlates poorly with the refraction cylinder.

During the examination, the patient sits in front of the skilled technician performing the ultrasound test. He/she is asked to fixate at a point straight ahead. The ultrasound soft probe is positioned axially, touching the corneal epithelium as lightly as possible so as not to compress and thereby shorten the eye. It is useful to visualize the procedure laterally to make sure that the cornea is not being compressed (Fig. 24).

Targeting Post-Op Refraction

This parameter is the only one that the physician must decide upon by himself and feed into the computer. All the other parameters are measured or assumed values over which hehasnocontrol. Whenselectingalens implant power Gimbel generally recommends that the surgeon target mild myopia and thus avoid inadvertent postoperative hyperopia. A patient who is hyperopic postoperatively will need spectacles for clear vision at any range, whereas a patient who is slightly myopic will have a range of clear vision corresponding to the degree of myopia. In all cases the patient must be counselled with regard to expectations of refractive changes and they should be counselled that they will generally need reading glasses or bifocals postoperatively as the implant has no power of accommodation, unless thepatient'stargetedpostoprefractionisaround -2.00 on purpose.

Monocular Correction

Holladay has pointed out that with monocular correction, there are two major considerations for determining what would be the best postoperative refraction for any patient. If we are only considering one eye (i.e., the other eye is amblyopic), targeting the postoperative refraction for approximately -1.00 to -1.50 diopters is probably the best choice.

This is usually best because most people have visual needs for both distance and near; that is, they want to be able to drive and to read without having to wear glasses. If we target the patient's post-op refraction for -1.00 to -1.50, the patient will have 20/20 vision at approximately 2 to 3 feet, 20/30 vision in the distance, and 20/30 at 14 inches. With a normal size pupilofapproximately3mminthecataractage

group, these visual acuities are adequate with no additional glasses required. At times when they might need finer acuity, they can wear regular bifocals, which will correct them for distance and near.

In older, more sedentary patients, two diopters of myopia may be a better goal. For these patients reading without glasses may be preferred to distance vision without glasses.

The second reason for targeting the postop refraction to approximately -1.00 to -1.50, sometimes -2.00 diopters, is that, statistically, between 70% and 90% of patients will fall within + or -1.00 diopter error of this desired postoperative refraction. The errors, as mentioned previously, are primarily a result of our inability to make exact measurements on the living eye.

Therefore, the patient will fall between plano and -2.00 diopters 90% of the time. This will assure most patients of useful vision without glasses. Hence, the error of the ultrasound measurement is best handled by choosing the postoperative refraction of -1.00. On the other hand, if we target for plano, which is the target that some physicians try to obtain, 90% of the patients will be between -1.00 and +1.00 diopters. When the patient's refraction is on the +1 side, he has less useful vision at any distance because he is hyperopic and does not have the ability to accommodate.

Consequently, because it is very undesirable to have a hyperopic correction, targeting for -1.00 not only optimizes the best vision at all distances but also minimizes the chance for hyperopia that can result from the inaccuracies of ultrasonic measurements.

Holladay's recommendation for choosing -1.00 to -1.5 as the postoperative refraction is based on one eye only, i.e. monocular conditions. When the vision in the other eye is good, its refraction must be considered for binocular vision.