Formula for Success

Learn how LRIs, accurate biometry and careful preparation can elevate your practice.

Maximizing Refractive Outcomes in Cataract Patients … Managing Astigmatism in Cataract Surgery … Optimizing Outcomes with New IOLs …

The articles in this section recap presentations given during an Ophthalmology Management seminar held during the 2007 meeting of the American Society of Cataract and Refractive Surgery.

Many of today's younger cataract patients have minimal cataracts and maximum expectations. These new patients typically pay their own way, similar to patients seeking plastic surgery. And like cosmetic surgery patients, they have high expectations for their surgery. The range of IOLs available today can produce a wide spectrum of outcomes, so selecting the right lens to meet the patient's expectations is increasingly important. Just as we've seen tremendous improvement in phaco machines, we've seen significant progress in every generation of lenses. What we're finding is that IOLs of all types — including the refractive, multifocal and accommodative lenses — eventually perform at very high levels. Technology will always get better and better, and we'll accomplish large advances in our ability to restore a full range of high quality vision to our patients. We also must consider using evolving surgical techniques, such as limbal relaxing incisions, advances in phaco fluidics and less invasive methods, to offer better postoperative vision. In this special supplement, we'll present information to help you achieve the best possible treatment results. — Uday Devgan, M.D., F.A.C.S.

Maximizing Refractive Outcomes in Cataract Patients

Today's cataract patients expect more than ever before. Four key steps and careful preparation will help you exceed their expectations.

BY UDAY DEVGAN, M.D., F.A.C.S.

Refractive surgery patients have high expectations, and choosing the right surgical treatment option for each specific patient is a challenge. When I partnered with a prominent refractive surgeon who performed more than 40,000 LASIK procedures, I found that my cataract patients from this practice had a distinct mindset. In such a setting, expectations are high, and our need to embrace the newest technology and the full spectrum of surgical options is great. Here, I'll review four steps that you may find helpful in developing your refractive cataract and lens practice.

Step 1: Improve Your Accuracy

There are multiple, good IOL calculation formulae, including more complex equations, such as the Holladay 2 and Haigis, which incorporate multiple variables. For most surgeons, using a good, yet simple theoretical formula is often easier and just as accurate. Which formula will yield the most precise lens calculations? For short eyes, I prefer a Hoffer Q equation (axial length < 22.00 mm); for average eyes (22.00 to 24.50), the average of the three common IOL formulas (Holladay 1, SRK/T and Hoffer Q); for slightly longer eyes (24.5 mm to 26 mm), the Holladay 1; and for even longer eyes (greater than 26 mm), the SRK/T. This is from a large study by Kenneth J. Hoffer, M.D.,¹ and I've found it to be quite accurate.

Be careful in determining the true corneal power with patients who've had LASIK. There are many methods for determining the true K power after LASIK, which means that none of them are perfect. Without a clinical history, I've found the most accurate formula to be one described by Douglas D. Koch, M.D.² It only requires the central K reading from topography or the average of the 0 to 3 mm zones. Simply, it is:

Ktrue = 1.114 x Ktopo – 6.1

This simple formula gives surprisingly accurate results, which are particularly helpful if you don't have a patient's previous records.

The refractive cataract patients want to be emmetropic or plano, so they'll find even a slight post-op correction unacceptable. Your options are IOL exchange, a piggyback lens, PRK, LASIK or conductive keratoplasty (CK).

If you're not comfortable performing LASIK or PRK to finetune your results, collaborate with a local refractive surgeon. Teamwork can improve outcomes and patient satisfaction.

Step 2: Address the Astigmatism

It's important to know the astigmatic effect of your incisions in routine cataract surgery. In order to determine the astigmatic effect of your incisions, look at the charts of your last 20 patients. What were the pre-op K values as compared to the post-op K values. For most surgeons, there is a flattening of about half a diopter on the axis of the incision. For mild cases of astigmatism, just making your incision on the steep axis may be enough. For larger degrees of astigmatism, you'll find limbal relaxing incisions (LRIs) to be of importance in reducing astigmatism.

For LRIs, keep these points in mind:

■ There is a corneal coupling effect. We make LRIs on steep meridians, and the power we take away is added to the flat meridian, creating the coupling effect. The net spherical equivalent doesn't change. Whether you do the LRI or not, your lens calculation will stay the same.

■ Beware of larger incisions. The larger or longer the incision, the more flattening you'll see in that meridian. If you make the incisions more central, they'll have a stronger effect, similar to an astigmatic keratotomy.

■ Incision depth determines effect. Remember that nonpenetrating, shallow LRIs cause less flattening. Any cut that's less than 50% in depth has almost no effect, and deeper cuts cause more flattening. But be careful. Anything deeper than 90% may lead to perforation.

For my beginning resident surgeons, I prefer to use a nomogram developed by Kevin Miller, M.D., UCLA. I perform just 1 clock hour of paired incisions on the steep axis for each diopter of corneal astigmatism. For each diopter of cylinder, I make 1 clock hour of paired LRIs. For 3 diopters of cylinder, I make 3 clock hours of paired LRIs.

■ Make sure you double-check the axis. There's nothing worse than making your incision on the wrong axis, when you're off by 90°. You'll double the astigmatism instead of reducing it.

■ Don't over-correct the cylinder. Patients accustomed to looking at the world through 2 diopters of cylinder at 90° probably will be happy with a half diopter of cylinder at 90°. If you try to achieve the exact spherical target and over-correct, you'll flip their axis, leaving them at a steep 180°, and they won't be satisfied.

■ Don't damage the corneal epithelium. Many LRI blades are designed to glide very smoothly along the corneal epithelium. To further enhance this. I coat the cornea with a dispersive viscoelastic, and then rinse with a balanced salt solution to prevent clumping of the viscoelastic.

Step 3: Minimize Complications

Patients who pay out of pocket for cataract surgery and premium IOLs expect a lot in return, including clear vision almost immediately. Minimizing the trauma to the corneal endothelium will result in clear corneas immediately after surgery. In this light, we use phaco chop and a viscoelastic to reduce the risk of complications. Use of phaco power modulations also allows us to use very little ultrasonic energy. When confronted with a dense nucleus, I'll stop and recoat the endothelium with more viscoelastic for added protection.

More capsules are broken during irrigation-aspiration (I/A) than during phaco. I've found that a silicone-coated, soft irrigation- aspiration tip can reduce the risk of a broken capsule. These are available from MST (MicroSurgical Technologies).

I avoid cystoid macular edema by treating every patient with nonsteroidal anti-inflammatory drugs (NSAIDs) 3 days before surgery and for 6 weeks after the procedure. Subclinical CME may not be seen on slit-lamp exam but can be picked up using optical coherence tomography (OCT) to evaluate the macula.

Step 4: Exceed Expectations

The sure way to patient happiness is to provide an outcome that's better than your patient expects. Use a questionnaire, such as the Dell Survey from Steven Dell, MD, to identify and address unrealistic expectations (see Figure 1).

Medicare-age patients don't expect their plastic surgeons to make them look like 21-year-olds again. Similarly, I tell patients that while I can certainly make their vision better, I cannot give them the visual function of a teenager. They understand immediately and agree that there's no fountain of youth.

Careful consideration of a patient and his expectations also is important when trying new technology. For example, when using a new lens, start with a patient who has posterior subcapsular cataracts, cortical changes, problems with glare and best corrected vision that's worse than 20/40. Anything that you do will be an improvement in the patient's vision and quality of life.

FIGURE 1

As one patient told me, "Doc, you told me I was going to have some glare with this lens. When is that going to come?"

I said, "Well, don't you see this now?" as I simulated the night vision effects.

"Oh, yeah, but it's much better than before."

Easygoing patients are willing to adapt, and they're not looking for perfect vision.

You Hold the Key

Remember the four steps. If you follow them, you'll improve your chances of success in this new era of refractive cataract surgery. As technology improves, new doors will open and your practice will continue to grow.

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Uday Devgan, M.D., F.A.C.S., specializes in cataract and refractive lens surgery at the Maloney Vision Institute in Los Angeles.

References

1. Hoffer KJ. Clinical results using the Holladay 2 intraocular lens power formula. J Cataract Refract Surg. 2000;26:1233-1237.

2. Koch DD. New options for IOL calculations after refractive surgery. J Cataract Refract Surg. 2006;32:371-372.

Managing Astigmatism in Cataract Surgery

Here's a primer on the latest surgical approaches to keep your practice on the cutting edge.

BY JONATHAN B. RUBENSTEIN, M.D.

The goal of cataract surgery today is to achieve emmetropia or to balance vision with the fellow eye. We manage the spherical component with the proper IOL power, using the IOLMaster (Carl Zeiss Meditec, Dublin, Calif.) or employing immersion ultrasonography. We manage the astigmatic component at the time of surgery by controlling the size and location of the wound, adding intraoperative relaxing incisions, or in the postoperative setting, using astigmatic keratotomy, wound revision or laser treatment.

Control of astigmatism is especially important when we use phakic, accommodating and pseudo-accommodating lens implants.

Choosing the Right Incisions

We can manage astigmatism intraoperatively with midcorneal, peripheral corneal or limbal relaxing incisions (LRIs). Consider the following:

■ Astigmatic keratotomy (AK) incisions: We make these incisions at 90% to 95% depth usually in an arcuate (A-cut) or transverse (T-cut) shape at a 7 mm or 8 mm optical zone at the conclusion of cataract surgery. Design and technique for these incisions is the same as for postoperative reductions of astigmatism.

■ Peripheral corneal relaxing incisions (PCRI): We make these incisions at 90% depth, in front of the limbus, in the steep meridian of the cornea. Because the incisions are near the limbus, they heal faster, resulting in a refractive effect that stabilizes more quickly. You also encounter less irregular astigmatism, glare and foreign body sensation compared to what you would find after making more central corneal incisions. Therefore, peripheral corneal relaxing incisions are the preferred technique.

PCRI Technique

The most important step is ensuring that your orientation is precise and accurate. I like to confirm the 6 o'clock position on the eye. If you wait to mark the patient's axis of steep astigmatism until he's lying down with one eye covered, you'll be deceived because of the torsional rotation that occurs in that eye once the opposite eye is occluded.

The easiest approach is to have the patient sit up on the edge of the bed in the holding area and ask him to look at your nose with both eyes open. Then, make a single mark at the 6 o'clock position with a surgical marking pen. This provides a reference point so you'll know exactly where the 6 o'clock point is with both eyes open. Then, in the operating room, I identify and mark the steep corneal axis using a marked fixation ring, astigmatic ruler or arcuate marker.

Make the paracentesis as you normally would, instilling nonpreserved lidocaine and adding epinephrine for patients who are on medications for the prostate gland. Fill the eye with a viscoelastic solution through the paracentesis.

Make sure the eye is firm before making incisions. Measure the thinnest limbal corneal thickness and set the diamond knife, or use a diamond knife preset to 550 microns or 600 microns. The peripheral cornea is always thicker than 600 microns unless there is pathology. So a very good slit lamp examination is in order to make sure the patient doesn't have previous corneal scarring, dellen formation, an irregular surface or some other relevant problem at the proposed PCRI incision site.

Proceeding with Surgery

Make your incisions before cataract extraction, using a single or double footplate front-cutting diamond blade. One can correct from 1.00D to 4.00D of astigmatism, basing your technique on one of many established nomograms, including:

■ Gills/Fenzel
■ Nichamin
■ Koch millimeter
■ Koch degrees

Make limbal incisions, single or paired, based on the patient's age, the amount of astigmatism and the desired refractive effect. For example, if a 75-year-old patient has 2.50D at 180°, use paired 45° cuts (Koch) or paired 50° cuts (Nichamin) at the 180° axis.

Intraoperative management of astigmatism can be achieved with mid-corneal, peripheral corneal or limbal relaxing incisions.

Next, create the normal clear corneal temporal wound for cataract removal. If the astigmatism is against the rule, make the cataract incision within a 3 mm limbal relaxing incision, being careful not to widen the wound. Only after the lens is implanted and the eye is filled with viscoelastic should you extend the PCRI incision further. If you make the 180° PCRI incision at its full length, manipulation of the phaco tip within this incision could tear out, resulting in a phaco wound larger than 3 mm and therefore a leaky wound. Also, try to center the incision on the axis of the measured astigmatism.

For with-the-rule surgery, don't cut through your paracentesis and avoid crossing incisions. I prefer to make my paracentesis more peripheral and my PCRIs a bit more central to make sure the two don't intersect.

Calculate the IOL power as you normally would. Peripheral relaxing incisions produce no change in spherical equivalent.

Complications to Consider

When performing limbal relaxing incisions, prepare for these common, potential complications:

■ Overcorrection and undercorrection. Undercorrection, which can be fixed by extending incisions, is less of a concern. Overcorrection can be a problem, especially if you induce a flipped axis. Remedying this overcorrection may require suturing the PCRI incisions closed to reduce their effect.

■ Perforation. You can avoid this with a careful preoperative slit lamp examination. Before surgery, you should decide if the patient needs an LRI, and where you'll place it. Visualize that portion of the cornea preoperatively to assure that no corneal thinning exists at the site of the proposed incision.

Mark the 6 o'clock position on the patient's limbus with the patient sitting up or lying down, looking straight ahead with both eyes open.

■ Wound leak. This can occur when the relaxing incision is made coincident with the cataract wound at 180°. You can tear through an incision during surgery. Also, remember to separate the paracentesis incision from a with-the-rule LRI. A suture may be necessary.

■ Foreign body sensation. Some patients will experience foreign-body sensation for the first 24 hours after surgery. Epithelial plugging may need to be cleaned out postoperatively if it's causing the wounds to gape. This plugging may be cleaned out at the slit lamp with a 25-gauge needle. I also use a fourth-generation fluoroquinolone q.i.d. for one week routinely to protect against infection.

Primary Goal

All cataract wounds will produce flattening in the axis of the incision and steepening (increased plus cylinder) 90° away. You should always have an idea of the amount of astigmatism induced by your cataract incision so you can accurately plan the appropriate length and location of the PCRIs needed for your surgery. Remember that our primary goal is to improve uncorrected vision.

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Jonathan B. Rubenstein, M.D., is the vice-chairman and the Deutsch Family Professor of Ophthalmology in the department of ophthalmology at Rush University Medical Center in Chicago, as well as chairman of ophthalmology at Rush North Shore Medical Center in Skokie, Ill.

Optimizing Outcomes with New IOLs

Here's an overview of the newest lenses, with guidelines for making accurate calculations and using biometry correctly.

BY FARRELL C. TYSON, M.D., F.A.C.S.

New intraocular implants have raised the stakes, compelling us to provide optimal cataract surgery, address presbyopia and produce unprecedented refractive outcomes at the same time.

As a cataract and glaucoma surgeon who participates in numerous clinical trials, I've used a wide variety of lenses, and I've learned how to use precise biometry to implant them effectively. Here, I'll share my experiences and insight.

How to Use New IOLs

To achieve ideal outcomes with these lenses, you need to get within 0.25D of your target refraction. This can be a challenge because of the design and technological variability associated with these lenses. Implants are allowed to be plus or minus about 0.25D off labeling, which adds some uncertainty.

To ensure accuracy, I recommend using reproducible keratometry and accurate axial lengths. Noncontact ultrasonography is also critical. I use an immersion A-scan with multiple error-checking or gating. Because you have two focus points with multifocal optics, your biometry must be accurate to avoid shifting your patient's distance vision and near vision focus points.

This slide depicts unoptimized formulas for intraocular lens calculations.

I always aim for plano. An outcome between -0.25D and +0.25D sphere is tolerable. With the ReStor lens, I find that patients can tolerate +0.25D sphere, leaving them in a much better add range from +3.25D to +2.75D. The ReZoom lens offers somewhat less add — about +2.75D to +2.25D.

IOL Calculations

Managing IOL calculations is critical. The third-generation formulas, which are based on broad assumptions, a schematic eye and theoretical constants, include:

■ Holladay I for normal, slightly long eyes
■ Hoffer Q for shorter eyes
■ SRK/T for longer eyes.

This slide shows the outcome of simple optimization of all formulas. Note the regression to the mean. You have lost accuracy in the extremes of axial length.

These formulas primarily work off of keratometry values and axial length, and therefore use a proportional measurement to determine the effective position of the IOL. These are imperfect estimates, raising the potential for unwanted surprises for patients who've undergone LASIK.

The Haigis formula, developed in 1991, uses a true measured anterior chamber depth, determining the true lens position. The anterior chamber depth measurement isn't as reproducible on the IOLMaster (Carl Zeiss Meditec, Dublin, Calif.) because of technician involvement. I avoid variability by using the Accutome immersion A-scan, which provides highly accurate measurements of the anterior chamber depth.

The Haigis formula has three constants:

■ a0, optimized similar to third-generation formulas
■ a1 and a2, based on the schematic eye.

You need at least 200 eyes to optimize the a1 and a2 constants. In simple optimization, where only a0 is used, your results are similar to a two-variable formula.

The Holladay 2, developed in 1998, is easy to optimize. It uses the anterior chamber depth as the constant but requires the input of seven variables, including axial length, white to white, corneal diameter, anterior chamber depth, lens thickness, patient's age and preoperative prescription. You must buy extra, stand-alone software to use this formula.

Optimization, limited by regression to the mean, requires 25 patients with the same implant. We're currently using 10 lenses with the formula, requiring 250 pristine cases for basic optimization. Complicated cases and those involving LRIs shouldn't be used in the optimization process. Even with optimization, predictability declines at extreme axial lengths. See the figures on page 6 for a visual presentation of how these formulas are applied and optimized.

Multiple optimizations, based on axial length, are shown in this slide, which allows for greater accuracy over a larger axial length range.

Moving Forward with the Implantable Collamer Lens

The Visian Implantable Collamer Lens (ICL) (Staar Surgical, Monrovia, Calif.) and the Visian Toric IOL, which is awaiting FDA approval, offer great promise with their new technology. Because the Visian ICL treats 3.00D to 20.00D of myopia, typically involving abnormally large eyes, it requires very precise measurements to achieve the best results. The ICL also requires peripheral iridotomy at 11 o'clock and 1 o'clock. About 3 mm or more of anterior chamber depth is needed, so obtaining good measurements of the anterior chamber is essential. You'll need to send your measurements to the manufacturer before surgery. One lesson we learned is that the axial length data isn't related to the calculation of the power of the ICL, which is based on the anterior chamber depth and the white-to-white measurement. I use my immersion A-scan because it measures anterior chamber depth more accurately than other devices. This measurement, along with white-to-white, is extremely important when determining if your patient needs large or small ICLs. — Farrell C. Tyson, M.D., F.A.C.S.

Precision and Persistence

Our machines are improving, providing better errorcorrecting information. But we still need to do a good job of analyzing the results of keratometry and our Ascan measurements to be successful in this new complex world of IOL technology. Our commitment to excellence in this area must remain constant.

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Farrell C. Tyson, M.D., F.A.C.S. is a refractive cataract/glaucoma eye surgeon at the Cape Coral Eye Center in Florida.