Given the increasing importance of highly precise intraocular lens power calculations, and the steadily increasing number of cataract patients with prior corneal refractive surgery, many surgeons are considering an option not often used in the past: refracting patients during surgery, while they're aphakic. This can be done using the wavefront-based ORange system (WaveTec, Aliso Viejo, Calif.), or by simply refracting the aphakic patient at the slit lamp and using a formula to translate the refraction into an IOL power. Here, experts familiar with both approaches discuss each method's pros and cons.

 

The Wavefront Approach

ORange , the first intraoperative wavefront aberrometer, is composed of an optical head that attaches directly to the surgical microscope that's connected to a computer processor and touch-screen monitor. When the patient is on the table and aphakic, the instrument can capture a wavefront measurement of the eye and use that data to calculate the eye's aphakic refraction. (The instrument uses Talbot-Moiré interferometry rather than Hartmann-Shack wavefront technology; the former allows measurement of a greater refractive range, and the use of smaller, less cumbersome equipment, more suitable for incorporation into the surgical field.)

When the surgeon believes ORange is appropriate for a given patient, the patient's data is entered into the instrument before surgery. During surgery, a menu allows the surgeon to select the desired function (refraction, limbal relaxing incision, toric IOL or IOL power calculation). The patient fixates on an internal light source, allowing the surgeon to align the instrument with the visual axis. Once activated, the system acquires and analyzes 40 images in about 20 seconds.

Eric D. Donnenfeld, MD, clinical professor of ophthalmology at New York University Medical Center and a partner at Ophthalmic Consultants of Long Island, has used WaveTec's ORange system for about five years. "At first we used the system as part of the clinical trial; then we began using it routinely in my practice for cataract surgery patients with special needs," he explains. "I don't think there's any doubt that we're getting better results. I've seen a very significant improvement in our outcomes."

Dr. Donnenfeld says the system has helped him get refractive results right the first time. "In the past, certain patients had a higher risk of ending up with residual refractive error and reduced vision," he says. "My experience is that you only get one chance to make a good first impression; getting it right the first time is much better than going back and doing an enhancement. If I can reduce my postop refractive surprises and improve my acuities the first time around, my practice will benefit."

Farrell C. Tyson II, MD, who practices at Cape Coral Eye Center in Cape Coral, Fla., has used the ORange system for about two years. "Once you take the cataract out, the aberrometer gets a very accurate measurement of the eye because you don't have the cataract adding noise into the system," he notes. "It determines the true power of the eye and then back-calculates what lens power needs to be implanted. The preoperative formulas most surgeons use are based on theoretical and mathematical data; they're more of a best-guess based on axial length and keratometry."

How does the ORange system compare to the IOLMaster in terms of outcomes? "Most of the time it matches the IOLMaster results, but sometimes they're a little bit different," says Dr. Tyson. "In the clinical trial, they performed a series of surgeries using different lenses, and the data indicated that the ORange aphakic calculation was producing a more accurate result than the IOLMaster. Even with the Alcon SN60WF, the ORange system got within 0.17 D of the target refraction. Warren Hill's theoretical limit is 0.18 D. So you're getting unbelievably accurate results with the aphakic power calculations."

Dr. Donnenfeld's group recently performed a retrospective study comparing outcomes between eyes measured using ORange and eyes with lens powers chosen based on traditional preop measurements and widely used lens power formulas. (The results were reported at the 2010 meeting of the European Society of Cataract and Refractive Surgery.) 

They compared results for a mix of lenses, as well as numbers for specific lens types. The data showed:

• Overall, using intraoperative aberrometry on 153 eyes resulted in 75 percent being ±0.5 D; 98 percent were within ±1 D. A published study using traditional approaches¹ resulted in 46 percent within ±0.5 D, and 85 percent within ±1 D.
• With Bausch + Lomb's Akreos MI60L, at one month postop, 85.7 percent were within ±0.5 D using the intraoperative aberrometer; 68.6 percent were within ±0.5 using a standard calculation method.
• With Alcon's AcrySof SN60WF, 100 percent were within ±0.5 D using ORange; 84.6 percent were within ±0.5 D using a standard method.
• With AMO's Tecnis ZCB00, 84.4 percent were within ±0.50 D using ORange; 46.9 percent were within ±0.5 D using the standard method.

 

Treating Astigmatism

Dr. Donnenfeld first used ORange for patients who were having limbal relaxing incisions or toric IOLs. "The system allows me to improve refractive cylinder and UCVA," he says. "One of the great urban legends is that the same incision induces the same amount of cylinder in every patient. That's just not the case—we've seen some significant differences between patients. Furthermore, if the axis of a toric lens is off by five degrees, you get a 15-percent reduction in correction. With the new toric lenses that correct 3 or 4 D of cylinder, that's a 0.5-D difference in your postop result.

"With ORange, we can do a pseudophakic refraction after the lens is implanted," he continues. "A screen pops up that tells us the current refraction and how much to rotate the lens. (For example, see p. 38.) It gives us a real-time result that correlates with the postop visual acuity at one month. (See sample data, p. 40.) Our enhancement rate has gone down significantly since we began using this technology, and we don't have to preoperatively mark the toric IOLs."

Dr. Tyson says he has found the ORange system to be very helpful for toric lens placement. "I use it before lens implantation to pick which power to put in, and how much cylinder; after implantation I use it with the toric lens in place to make the appropriate rotation," he explains. "The machine may tell me to rotate the lens 6 degrees; I just nudge the lens and get another 0.2 D taken off the cylinder."

Dr. Tyson notes additional benefits as well. "The other thing I find is that about 30 percent of the time I'm changing the cylinder power of the IOL based on the ORange system results," he says. "The preop calculators are often too conservative. So, I'm eliminating more cylinder because the ORange is picking up the true amount. Furthermore, about 5 percent of the time I'm deciding not to put in a toric lens at all. So it's saving me from IOL surprises involving cylinder."

 

Post-Refractive Surgery Patients

Dr. Donnenfeld also uses ORange for patients who have had previous corneal refractive surgery. "There are dozens of formulas that can be used to make power calculations in this situation," he says. "In my experience they improve the results but still leave a lot to be desired. That's because the visual axis and the center of the cornea are not always in the same place, so the keratometries you get from either topography, manual keratometry or the IOLMaster don't always show the visual axis. And often after LASIK the measured keratometric values are higher than the actual powers. Furthermore, the anterior chamber depth and IOL position create inaccuracies in a lot of the formulas.

"Using real-time intraoperative aberrometry has allowed me to adjust my IOL power calculations and reduce my enhancement rate from 40 percent to less than 10 percent in post-refractive eyes," he notes. "That's a very significant improvement." Dr. Donnenfeld adds that he also uses ORange on high myopes and hyperopes, for whom the typical lens-calculation formulas become unreliable.

Dr. Tyson says the company is still working to improve the instrument's ability to produce accurate outcomes in post-refractive-surgery patients. "The newest software has a revised algorithm designed to be more accurate with post-myopic LASIK and RK patients," he says. "Right now, there are many different formulas for making those calculations—which tells us that there's no one ideal way to do it, at least so far. Having an accurate way to determine the best IOL power will make life a lot easier."

 

Concerns and Limitations

Surgeons familiar with the technology acknowledge that there are still issues to be resolved, as well as practical concerns that might discourage doctors from rushing to adopt the technology:

   • Effective lens position. "Effective lens position is the bugaboo of any lens formula," says Dr. Tyson. "But when you have better readings to begin with you'll end up with better outcomes. All instruments and formulas have to make assumptions about where the lens will be once the eye is healed, and despite that, we do pretty well 90 percent of the time. The ORange system is doing the same thing, but it's starting off with better data. So you still have the possibility of an unusual eye, where the lens ends up sitting a little more anterior or posterior than you expected. But in the majority of cases, the ORange system will be accurate."

Dr. Donnenfeld notes that this issue may explain the last 10 percent of patients who still require enhancements. "This is a first generation aphakic refraction system," he notes. "It doesn't correlate with anterior chamber depth yet. We're now working on the second-generation system, which should reduce the enhancement rate by taking ELP into account."

In the meantime, Dr. Donnenfeld says he deals with this by doing a pseudophakic refraction after the lens has been implanted. "In the rare case in which we're not happy with the result, we can do a lens exchange on the table right then and there," he notes. 

"In essence, we're getting the effective lens position by doing a pseudophakic wavefront aberrometry. I've only had to exchange a lens a few times, and I'd rather do that than have to see the patient again the next day and tell him that he's +1.5 D."

Dr. Tyson has also used the pseudophakic refraction approach, but says he's reluctant to trust the ORange system when he takes a power reading after lens placement. 

"Effective lens position hampers the ORange system in this situation," he notes. "That's because when you inflate the eye, you move the lens. The reading you get is accurate—it's just not realistic. When the eye heals, the pressure changes a little bit. Of course, for the aphakic calculations it's very accurate because there's no lens in the eye whose position is debatable." (Dr. Tyson adds that effective lens position has almost no effect on the accuracy of astigmatic positioning and measurements.)

   • Cost concerns. "The system costs about $50,000," says Dr. Tyson, "but you're saving money by not having to manage IOL surprises, do enhancements or touch things up. There's also the cost of making a new appointment, having your people change the billing, the technician having to do more workups. You eliminate all of these intangible costs by getting it right the first time. I suspect that some doctors think, 'I have a laser so I can just touch up the patient.'

But most cataract surgeons don't have a laser that's easily accessible, so using ORange makes a lot of sense." (Dr. Donnenfeld says he offers this option to patients he believes might benefit from it, for an extra fee; thus he's reimbursed for his time and effort.)

Should a surgeon who is thinking about offering premium lenses consider investing in the ORange system? "I'd advise someone in that position to wait," says Dr. Tyson. "It's a great instrument, but they can still improve on it. And if you're not doing premium lenses already, then you probably haven't invested in some of the other technologies that would be more beneficial immediately. Of course, the extra cost is harder to justify if you're not offering premium or toric lenses."

   • Learning curve. Dr. Donnenfeld doesn't see this as a major concern. "There are some tricks to using ORange," he notes. "You have to hyperinflate the eye; make sure the eye is perpendicular; avoid corneal edema; get all viscoelastic out from behind the lens; and make sure the lens is in good position. As with most technologies, there are little nuances that users need to learn in order to get the best results. But it only takes a few cases to learn them."

   • Other issues. "I think surgeons expect a point-and-shoot device," says Dr. Tyson. "It's coming closer to that, but it still takes a little bit of interaction with the patient and the device to make sure you understand what the information is telling you. The new software is supposed to catch an erroneous reading automatically, but this is still being fine-tuned."

Some surgeons also find the physical configuration challenging. "There's only one working range," notes Lance S. Ferguson, MD, in private practice at Commonwealth Eye Surgery in Lexington, Ky., and president of the American College of Eye Surgeons. Dr. Ferguson recently began using the ORange system for the first time. "The objective lens is 200 mm, where I normally use a 250-mm lens. That forces me to crouch over—uncomfortable from a cervical spine standpoint. When I use the ORange, I have to drop the microscope down a couple of inches just to get it into the ballpark. You can bang your instruments against the bottom of the machine and contaminate yourself or your gloves. I'd prefer a 250-mm lens." (Dr. Donnenfeld agrees that this is a potential concern, but says that he quickly adjusted to the decreased working distance; it hasn't been a problem for him since then.)

"Ultimately, I'd like to see the instrument provide even more data," says Dr. Tyson. "I'd like to be able to analyze spherical aberration; then you could pick the right IOL in those terms. But the machine has only been on the market for about a year and a half, and they're making lots of strides forward. Every time we use it it seems better."

 

The Mackool Method

Despite the recent appearance of the ORange system, the idea of performing a refraction while the patient is aphakic is not new. Richard Mackool, MD, PC, director of the Mackool Eye Institute and Laser Center and senior attending surgeon at the New York Eye and Ear Infirmary, has used a lower-tech method to accomplish the same feat in difficult eyes for the past 15 years.

In Dr. Mackool's method, after the lens is removed and IOP is restored to physiologic levels, the patient leaves the operating room. After waiting 45 minutes to an hour, the patient undergoes manual refraction. Depending on the circumstances, the patient then returns to the OR or goes home and returns the following day for a second refraction, at which point the appropriate IOL is implanted. The IOL power is calculated using a conversion factor that is based on the lens's A-constant and the value of the aphakic spherical equivalent. (For the complete formula, surgeons can contact Dr. Mackool at mackooleye@aol.com.)

Dr. Mackool says that he's used this technique on approximately 2,000 patients. "I use it about five times per week, and I've been doing this for 15 years," he says. "We started out using the technique on posterior staphylomatous eyes; at that time, we only had ultrasound—no optical biometer such as the IOLMaster. After the advanced version of the IOLMaster became available, we didn't need the technique very often because we could use the new technology to get good readings in many of those eyes.

"What has increased in recent years is the number of post-LASIK eyes," he continues. "When surgeons encounter eyes that have had previous corneal refractive surgery, they may use any of a number of formulas to try to guesstimate the correct lens power needed, but we've found that our aphakic refraction technique is more reliable than any of the other methods. In addition, we use this technique for other types of eyes that are problematic with optical biometry: a patient with nystagmus, where you can't get a good axial length reading no matter how hard you try; a patient with an irregular corneal surface, where you can't get decent keratometry; and certain types of vitreous opacities that give you inaccurate readings in spite of your best efforts. We encounter plenty of cases like these."

 

How It's Done

Dr. Mackool describes the method as he and his practice colleagues currently use it. "First, we remove the cataract and the patient leaves the OR," he says. "About 45 minutes to an hour later the patient undergoes an aphakic refraction. Then, most patients are instructed to go home with the eye still aphakic and return the following morning. When the patient returns, we repeat the refraction.

"The reason for the second refraction," he continues, "is that some patients who've had LASIK may have an inaccurate refraction because the pupil is dilated right after cataract surgery. The next morning, the pupil is nondilated, which can give us a more accurate refraction. Also, patients often have better visual acuity at one of the two refractions—most commonly the following morning. With better visual acuity, you can have more confidence in the refraction; patients are much more certain when they decide which is better—one or two?

"Once in a while we'll have a patient for whom it's not feasible to return the next day," he adds. "In that situation, we do the same-day aphakic refraction after waiting an hour and use that value. But my preference is to get the refraction done the next morning with the smaller pupil."

Dr. Mackool acknowledges that most surgeons are not accustomed to sending patients home with an aphakic eye. "We've never had a patient complain about this," he says. "You simply explain the reasons for your instructions and tell the patient that for that one night his vision will be similar to opening your eyes under water. I say, 'Go home, rest and come back in the morning and we'll put the implant in.' Patients accept this very well. They never come back and say, 'Last night was terrible.' "

Dr. Mackool says that patients do care about the reason he's doing things this way. "I explain that I'm taking a short operation and dividing it into two even shorter operations," he says. "I tell the patient: 'I can take a guess at the power we should use for this implant, and maybe I'll be right. Or we can try to get more information and increase our chances of the implant being accurate for you.' I've never had a single patient say they'd prefer that I use the quicker, less accurate approach."

Does the technique produce good outcomes? "Our success rate and accuracy is very high," he says. "It's very rare that I have to change implants in a post-LASIK eye; in fact, I can only recall exchanging an implant three or four times in the 15 years I've used this technique. Patients nearly always end up within a half-diopter of the desired result, and our statistical mean is within a quarter-diopter of the intended result."

 

Addressing Concerns

Some surgeons familiar with this technique express concern about what they describe as entering the eye twice, and the potential for increasing the risk of endophthalmitis. "Such concerns are unwarranted," says Dr. Mackool. "Not one of the thousands of patients we've used this technique on has developed endophthalmitis, and I see no reason to think that will change. And this is not 'extended surgery'; we're not duplicating any steps. Whether or not you divide the standard cataract procedure into two smaller procedures, you enter the eye twice. And each part of the procedure takes the usual amount of time."

Dr. Mackool believes that a key reason for his ASC's extremely low endophthalmitis rate is that the 35 surgeons who work there all inject vancomycin into the eye at the end of surgery. "Our ASC has done 60,000 consecutive cases without a single case of endophthalmitis, thanks to this protocol," he notes. "Some still consider this controversial because of the claim some time ago that this will induce bacterial resistance. But think about it: There's no way that a single injection into the eye can produce bacterial resistance; that's not how bacterial resistance works. Furthermore, a retrospective study done in Australia found that after this protocol was adopted the incidence of endophthalmitis dropped by a factor of 40.² Using this approach has basically eliminated endophthalmitis from our practice."

Does a surgeon need to work in an ASC to use the Mackool aphakic refraction approach? Dr. Mackool doesn't think so. "You just need an OR that you can get into twice," he says. "ASCs are typically more flexible than hospitals, so it might be easier for a surgeon to arrange for a patient to return the following morning. But beyond that, I think you could use this approach in almost any setting."

Dr. Mackool offers one important pearl for any surgeon trying this technique. "You have to be careful to keep the cornea lubricated after cataract removal," he says. "If you don't put a lubricating drop in at the end of the surgery, the patient sits in the waiting room with his eyes anesthetized and doesn't blink. You can then have trouble getting a good refraction, because the patient won't be able to see well through a dry corneal surface."

Dr. Mackool is not currently using the ORange intraoperative system, in part because he continues to have excellent outcomes using his lower-tech approach. "If automated retinoscopy and/or wavefront methods were perfect, we wouldn't bother to do manifest refractions," he notes. "We'd stick patients in front of a machine and have it print out the prescription. I think manifest refraction can be refined to a greater degree than any automated technique." He adds that he'd be happy to see a head-to-head comparison of the two intraoperative approaches, noting that he has nothing to gain, regardless of the outcome.

Dr. Mackool observes that people have a natural resistance to trying different approaches, especially if they believe there might be some risk involved. "I hope more surgeons will try this protocol for themselves," he says. "I believe this is the most accurate way to determine the IOL power for a patient in whom you otherwise can't do it. Our extensive track record shows that it works very well."

 

Dr. Donnenfeld is a consultant to WaveTec Vision. Dr. Tyson has no financial connection to any product or company mentioned. Dr. Mackool has no financial interest in his aphakic refraction method.

 

^{1. Narvaez J, Zimmerman G, Stulting D, Chang DH. Accuracy of intraocular lens power prediction using the Hoffer Q, Holladay 1, Holladay 2, and SRK/T formulas. J Cataract Refract Surg 2006:32:2050-53.}

^{2. Anijeet DR, Palimar P, Peckar CO. Intracameral vancomycin following cataract surgery: An eleven-year study. Clin Ophthalmol 2010 Apr 26;4:321-6.}