Today's cataract surgeons have the most advanced phaco machines and premium intraocular lenses available to them, and patient expectations regarding surgical outcomes are at an all-time high. Emmetropia after cataract surgery is a reasonable expectation for many patients. Often, the keys to achieving this result come down to surgeon technique and patient factors.
"This is a goal we have been striving for since we started doing cataract surgery," says Robert M. Kershner, MD, director of Eye Laser Consulting,
Now, not only are we going to remove the cataract and implant a lens, but we are going to get patients seeing better without glasses than before they had their cataract. In fact, what we'd really like to do is give them clear uncorrected near and distance vision."
However, this is not achievable in all patients. During preoperative counseling, it is important to make sure that patients have reasonable expectations. "It's not possible to get 100 percent of people to the point where they don't need glasses. During the counseling, some perspective from the surgeon on the reasonable amount of glasses use expected is important," says Robert J. Arleo, MD, in private practice in
Rajesh Rajpal, MD, agrees. "Patients frequently expect to not need glasses after cataract surgery, so it is critical to educate them properly on how close to emmetropia is realistic for them based on their individual prescription and healing variability, as well as the IOL they select," says Dr. Rajpal, who is in private practice at Cornea Consultants and See Clearly Vision Group, in McLean, Va.
Patient Expectations
According to Steven Dewey, MD, patients need to be educated about the difference between 20/20 vision and spectacle-free vision. "A patient may come in fixated on the number 20/20, but you may find out that he really wants to be able to work at the computer six hours a day without putting on a pair of glasses," says Dr. Dewey, who is in private practice in Colorado Springs.
He tells patients that, even with a great outcome, wearing glasses during some activities will make vision better. "You can have a husband and wife, each with a perfect monovision result from an anatomic and daylight functional aspect. One of them may have no trouble at all driving at night because she can suppress the myopic result in the fellow eye. The other patient may be driven crazy at night by the starbursts around headlights and may have to wear night driving glasses. The challenge is really trying to get into the heads of patients and figure out what they like about their vision and what they don't like about their vision. Short of that, it's a lot less chair time to warn them in advance about glasses for certain activities than explaining it after surgery when it may look like you're backpedaling," Dr. Dewey says.
Dr. Kershner notes that some patients may not be able to achieve 20/20 vision because they don't have a "20/20 brain." "Assuming no other pre-existing disease that would limit the successful outcome, people are lulled into thinking that everyone is capable of perfect vision, and they aren't," he says.
He explains that, rather than targeting 20/20, surgeons should target 20/happy, which is different for each patient. He notes that many patients with residual refractive errors are happy with their outcomes, while patients who have perfect outcomes on paper are not happy.
For the majority of cataract patients who desire reduced spectacle dependence, emmetropia in at least one eye is the surgical priority, says David F. Chang, MD, a clinical professor at the University of California, San Francisco, and in private practice in Los Altos, Calif. "With diffractive multifocal IOLs, in particular, the optical trade-offs will start to outweigh the benefits if there is significant residual refractive error—astigmatism in particular," he says.
Dr. Chang believes that surgeons must be careful not to promise more than they can confidently deliver, and that they should restrain patient expectations and explain the potential need for enhancements. "Post-LASIK patients are particularly problematic because they have the highest expectations and the worst refractive accuracy," he explains.
Measurements
Accurate preoperative measurements play an important role in surgical outcomes. "I think you should be using an IOL Master and a customized A-constant," Dr. Arleo says. "When looking at the calculations, I always look at the other eye's calculations. If a patient has had surgery in the other eye, I look at the targeted outcome and the outcome achieved. I also look for differences in the Ks or differences in the axial lengths." He notes that dry-eye patients can have significantly different measurements over two or three visits, and this can affect the astigmatism measurement. "I see fluctuations that are pretty significant, so look at your measurement in the context of the other eye's measurement and the patient's situation, and see if it makes sense," he adds.
Dr. Chang notes that while personalizing one's A-constant is valuable, it is an average. "It is equally important for us to reduce the standard deviation," he explains. "K readings are the most common source of error in many practices, because a printout of averaged readings does not identify how many poor readings (such as from poor fixation or a poor ocular surface) have contributed to the average." He believes it helps to use different instruments as a cross-check and to try to do these measurements during pre-testing before the instillation of topical anesthetic or mydriatic drops. If the readings are not consistent within and between different platforms, they may need to be repeated after the instillation of artificial tears.
Dr. Dewey notes that, even with accurate measurements, the final lens position will vary from patient to patient. And Dr. Rajpal explains that proper preparation of the ocular surface prior to surgery is critical in achieving the best postoperative outcomes. "This would include dry eye and blepharitis treatment such as cyclosporine A, azithromycin, artificial tears, warm compresses, lid hygiene, nutritional supplements, et cetera," he says.
Surgical Technique
Dr. Chang cites a commonly overlooked source of variability: inconsistency in the capsulorhexis size and shape. "Failure to fully overlap the edge of the optic can lead to subtle changes in the axial position of the optic, which represents the effective lens position, he says. "I find that the best way to achieve consistent capsulorhexis overlap is to err on making the primary continuous curvilinear capsulorhexis diameter on the small side. Once the IOL is implanted, I can enlarge the CCC in whatever region I need to achieve the optimal size and symmetry. For example, because of the nasal decentration of most pupils, I orient the ReSTOR with the haptics in the vertical axis and then nasally decenter the optic. I then trim the CCC as needed to symmetrically overlap the optic."
Dr. Arleo uses capsular tension rings in patients with pseudoexfoliation because these patients' zonules are weaker, so the stability of the implant is better.
According to Dr. Dewey, it is important to use IOLs that you have experience implanting.
"Anytime a surgeon uses a different model of implant than he or she has used previously, there are going to be some inaccuracies," he says. Additionally, he has found that stromal hydration has an inconsistent effect on astigmatism, so he does not use stromal hydration to ensure that the incision is watertight. He also notes that his patients are closer to their target refraction a year after surgery than they are at one month. "I found with a three-piece hydrophobic acrylic IOL, if there is a slight shift, the shift is slightly myopic in the range of 0.25 or 0.5 D," he says. "It's ultra-important for surgeons to look at patients they did a month ago as well as a year ago. The ones you did a month ago will tell you how far off your biometry is, but the ones you did a year ago will tell you where the long-term drift might take people."
Surgeon Experience
In some cases, emmetropia is not achieved after cataract surgery due to surgeon error. "It could be a function of poor measurements going in or it could be the surgeon not achieving surgical success despite his best efforts," says Dr. Kershner. "Just because you are capable and just because you want to doesn't necessarily mean that you will. If it was easy to do it each and every time, then we would do it every time. The fact that we don't always achieve it means that it's not as easy to achieve as some might believe."
He recommends starting with patients in whom you are most likely to achieve success.
"People think they should operate on someone who is 20/30 or 20/40 before surgery because it will be easier to make them emmetropic. However, the opposite is true. They have higher expectations. They will not be happy with 20/30, whereas someone who was 20/100 would be happy at 20/30," he adds.
The importance of experience is paramount. "All surgeons have the same technologies available to them, and most surgeons who have been trained adequately can do the procedure reasonably well," Dr. Kershner says. "However, when unforeseen complications arise during surgery, you're at the mercy of the experience of the doctor to handle the unexpected. With experience, you can take the patient who could be a catastrophe and achieve a great outcome."
